| Author | Message | ||
     Anonymous Rating: |
Hi, This topic has came up before and people have said it doesn't work. The plans say it will make a 19" tv a 100" projector. I do think it would be very dim at 100", but what about only 25 or 30 inches? Could it make a 19" tv a 30" projector? Here is one selling on Ebay(includes pictures)http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1215303832 The one I am thinking about buying is here: http://www.100inchtv.com | ||
| Anonymous Rating: |
10 bucks for a big Fresnel lens isn't a bad deal, really. As for making a useful projection system with a 19 inch tv: it would be very dim and blurry. A mirror or other image inverter will also be required (more light loss). Go to http://www.deja.com and search for 100 inch tv scam . | ||
| Anonymous Rating: N/A |
What about the picture they show on Ebay? http://imagehost.auctionwatch.com/bin/imageserver.x/00000000/fevrish/975984929-picture.jpeg It doesn't look dim or blurry? | ||
| Eric M. Lindstrom Rating: N/A |
Two words: Photoshop filter!!! ^_^ Sorry, but this doesn't work all that well unless: 1) you have High-quality optics 2) you have a Light-tight, matte black enclosure for your unit. 3) you have a reasonably dark room and a bright CRT in your display. A better method would be to take an LCD panel, and backlight that SOB with a projetor lamp! They also have LCD's which fit into a slide projector, cheaper than a projector by far. (Just remember to put a glass ballast between the LCD and the bulb in your homebrew rig, or that thing will melt, fans are good too!) Contrary to popular belief, most current LCD projectors should work with shutterglasses. the biggest problem used to be latency, but, most PC quality LCD projectors have refresh rates comparable to most CRT monitors, and TFT technology has fixed the latency problem for the most part. Before buying a projector, however, I suggest you rent one from a local A/V store to try before you buy. Dont forget, if you use multiple LCD projectors in your rig, and can't use shutterglasses, you can just polarize the projector output and use polarization glasses. You can order Polarization filters in bulk CHEAP from American Science & surplus center at http://www.sciplus.com They also carry military-grade optics (lenses mirrors, etc) as well as other stuff (Aura Bass Shakers for $5 I believe, nice for force feedback rigs) They are a godsend to any home VR enthusiast! They also have Frensel Lenses. Check them out if you need wierd bits of hardware for your setup, they usualy have the cure for your raw material needs. -Eric L. | ||
| Hyeron Rating: N/A |
Eric have you tried building a projector from an LCD and a slide projector? If so, have you succeeded in achieving acceptable quality? (in 2d I mean, let alone in 3d) Where did you get a high enough resolution LCD. I am thinking of buying a 'real' videoprojector but the running cost ($300-600 for a new lamp at 1500 hrs) bothers me somewhat! Besides it might be fun building something. About the stereo thing: most projectors I have seen have a max. frequency of around 85 Hz, wich might cause flicker in 3d? Thanks in advance, Hyeron | ||
| Anonymous Rating: N/A |
So this could work if I buy a high quality lense and make the enclosure light-tight, but what is matte black? I have a pitch black room and a 19" TV. Could I get a reasonable 2-D 30" picture? How far away from the screen does the unit have to be for a 30" picture? I was thinking about projecting onto a white sheet. Would it help if I bought a real projection screen? Thank you for your input :^) | ||
| David C. Qualman Rating: N/A |
This discussion is very heavy into the physics of optics. But, with the questions asked, particularly by Anonymous, there is not the understanding of these physics. I'll give a quick rundown, but you should really check into some high-school level or later physics text to fully understand. About the distance away: The lens equation can be written as 1/f = 1/D + 1/d where f is the focal length of the lens, D is the distance from the lens to the object (the screen), and d is the distance from the lens to the image (the projected image of the screen). If you know f and D, you can compute d. If you had a really, really bright image, then you could project the image. But, a monitor is not reallistically bright enough. (For simplicity, I will use the word "intensity" to represent the amount of light energy in an area. I will not try to take human sensitivity to light into account.) Let's assume that all of the light emitted from the screen goes through the lens and is focussed onto the screen. This requires a huge lens, about the size of the screen. This is pretty easy with a Fresnel lens. Now, the light energy coming out of the monitor is the light energy that is on the screen, but spread over a much bigger area. If the sizes are measured in one dimension, such as 19" diagonal for the screen, and a 30" diagonal for the image, then this is an inverse square relationship. That is I'/I = (S)(S)/((S')(S')), where I' is the intensity of light on the screen, and I is the intensity of light from the monitor, S' is the diagonal of the Image size, and S is the diagonal of the monitor. For the example, we see that the intensity of light on the wall is only 40% as that of the screen. To get a rough idea, turn the brightness on your monitor to 40% of what it is. Next we have the background lighting. The energy of light projected onto the screen is actually the energy added to the screen. It is added to the background light. If the room is well illuminated, it could easily be too hard to distinguish background lighting from the image, so almost no image will be seen. Thus, the room needs to be very dark. (Matte black is a term that means that a surface is so black that no light is reflected. Like the inside of a camera.) Now, with a dark room, you still need to reflect the light back to your eye. Two problems here. First is the reflectivity of the screen. This immediately cuts down on the energy that gets back to your eye. If the screen is only 90% reflective, then in this example, you would only reflect an image that is 36% as bright as the monitor. Next is the inverse square law. If you sit two feet away from the image, you will only see 1/4 of the intensity as you would at 1 foot. At 6 feet, you only see 1/36th of the intensity. So, with such a dim image, you need to sit pretty close to the image. Also, you need to sit to the side, or you will be in the beam of the image. Try sitting one foot in front of your 19" monitor, but always sitting to the side - never directly in front. I suspect that you would soon hate it from the neck cramps that you would get. Keep in mind that projectors use bulbs that are several hundred Watts in power. Your monitor puts out very few Watts from each point. This can be understood, because it is much easier to look at than even a 60 Watt light of about the same area. For example, look at a flourescent light, which may be two to three times the area as your monitor. These 40 to 60 watt bulbs are still much brighter than your monitor. Or, think about how bright your room is with just a monitor on and all other lights off. It is not even as bright as a little flashlight would make it. The idea that you could project images with such a dim light, and still get good results is almost laughable. | ||
| Anonymous Rating: N/A |
The Fresnel lens in American Science and Surplus says it is slightly tinted. Is there somewhere I can get a clear lense? | ||
| Anonymous Rating: N/A |
So if the focal length of the lens is 25" and the distance from the lens to the screen is 25" (I don't know how far away it has to be), how far away does the 19" tv have to be from the wall to project a 30" image? | ||
| Anonymous Rating: N/A |
I think I already have a Fresnel lens, but I got it wet a long time ago and now it has spots on it. Is there anyway to get rid of the spots? Thanks. | ||
| Eric Lindstrom Rating: N/A |
In response to Hyeron, No, I haven't tried building the slide projector version yet, but I saw one on the market. Looks easy enough. I took an old LCD palm-sized TV (I think it was a casio...) and rigged it into an old super 8 movie projector once. The film mechanisms were shot anyways, so I gutted it and used the fan, optcs and light source to make a projector. The main guts were connected to the LCD via extra wire, was a pain in the butt to solder, though. I put glass plates on either side of the LCD with about a 1/2 inch gap between the LCD and glass to create a ballast, and used tin sheets and built a shroud to direct the light to the LCD. Be sure to use hi-temp black spraypaint to make it black (Matte black, not gloss black!) Unfortunately, this rig bit the dust when the tuner died (as well as some of my soldering job :p ) I used a scan convertor to pipe PC output through it. It the TV you canabalize for the project is of the backlit variety, this will work. But if you use shutterglasses, look out! the ghosting & flicker will be pretty bad. I would reccommend using the 2-monitor setup (see other posts) and use two projectors w/two scan convertors and just use polarizers on the projectors. Still, dont forget that the projected image will lose some ghutterglass flicker due to the fact that it is projected (de-sharpens the image a bit) TFT displays would be the way to go, they refresh quicker. -Eric L. | ||
| Eric Lindstrom Rating: N/A |
This is Eric again. In regards to David C. Qualman's post; I found it extremely informative. I have added it to my personal library of DOCs. I have a question, what about going another route about this: What if the projection surface (hence forth, "screen") were 100% reflective, like a mirror, then the image would stay visible and bright. Maybe we're going about this the wrong way. What about a concave mirror say, 25 inches across, and rigged in such a way that it would only receive an image from a video source (hence forth, monitor) The picture would be great, the trick would be keeping surrounding light from reflecting as well (it would kill the effect if you could see yourself!) Just a different view in the issue at hand. -Eric L. | ||
| Eric Lindstrom Rating: N/A |
Final bit of info for other questins... 1) you can buy full-page, 8.5" x 11" frensel lenses from Office Depot. I find these lenses, manufactured by Appollo, very durable, good enough for your project, but may have some flaws. If you want higer-quality optics of this size, try a nature store (like natural Wonders, Store of Knowledge or the Nature company). 2) the spots can be removed. Use a plastic cleaner on a soft cloth, softly wiping around the lens along with the rings. Dont go against the grain or you'll scratch it! If the lens is scratched, you can't fix it. But new lenses are relatively cheap. 3) in sizing the image, it's best to experiment with different focal lengths until you ge the desired display size. it helps to tape a yardstick to the wall in gagueing the screen size. | ||
| David C. Qualman Rating: N/A |
If the focal length is 25", and the distance from the lens to the screen is 25", then it is physically impossible to position the image. Think of the focal point as where all of the light must converge on its way to the screen. If the screen is at that focal point, all of the light will be converged, hence no image. It is exactly what happens when you use a magnifying glass to burn ants. If the lens has a focal length of 4 inches, and the lens is 4 inches from the ant, then all of the energy from the sun that goes through the lens is converged onto the ant. Poof! But, if the lens is pulled back a bit, then the image of the sun can be projected onto the sidewalk. I have experimented like this by focussing a 60 Watt bulb onto a wall with a magnifying glass. If I move the lens backwards a bit, I can get an image of the bulb, or the lampshade, on the wall instead. This is exactly how you can measure the focal length of your lens. Take it outside, and focus the sun onto the sidewalk, or some ants. The distance the lens is from the ants when the light converges is the focal length. With a calculator, a little algebra, and the lens equaiton, you could see that if the focal length is 25", and the screen is 30" from the lens, the image will be 150" from the lens. I probably should have included the magnification formula as well. The magnification of an image is M = d/D, where M is the magnification, d is the distance from the image to the lens, and D is the distance from the object to the lens. Thus, for the example, we have M = 30/19, or 1.58. Thus, d = 1.58D. So, with the lens equation, and knowing that f is 25", we get 1/25 = 1/1.58D + 1/D This means that D = 40.8" (image or screen to lens). This gives d = 64.5". The entire setup will take 105.3", or 8.775 feet. As Eric suggests, one could try using mirrors instead of lenses. But, optically, they are almost the same thing. They have the same equation as the lenses, assuming that the mirror approximates a parabolic shape. The main difference is that the light through a lens may need to hit a screen first. But, with a mirror, the light gets back to the eye through a shorter distance. To see how the lens and mirror are similar, think about some of the HMD's. They put an object just past a lens in front of the eyes. Your eyes are the screen. This lens makes the object look big. Since it is so close, it can use very little light energy, unlike using a 19" monitor. The same would be true with a concave mirror. Put the screen beside your head, put a concave mirror in front of your eye aimed at the screen, and you have effectively the same setup. Except that the line of sight is off at an angle. The mirrors would need to be larger than the object. If you are using 2" monitors for instance, the mirrors would need to be larger than 2" in diameter. This depends upon the values chosen for f, D and d in the lens equation. (BTW: Eric, what is a DOC?) | ||
| David C. Qualman Rating: N/A |
Oh yeah, I just realized that Anonymous was talking about building one of these things with a Fresnel lens. Keep in mind that the image will be inverted from the object. That is, the image will be upside down. If you turn your monitor over, you could correct for it. Or, look at the image while standing on your head :-) | ||
| Eric Lindstrom Rating: N/A |
DOC: a short-form word meaning Documentation. I tend to keep archives of various bits of info on a couple different subjects. If I find information that I may find handy in my VR endeavors, I add the info to a text file I have on the subject for future reference. Whenever I talk about a piece of software, and I say, "Read the DOC's for more info..." I am refering to the software's documentation. As a matter of fact, most software will have a file in it's working directory with a .doc extension, which is a text file that contains documentation for that perticular program. Sorry if this was confusing. It's a bad habit of mine I have aquired from USENET posting ^_^ -Eric L. | ||
| Eric Lindstrom Rating: N/A |
Some more info for you people... David's last post was good as well, more info for my DOC's!!! ^_^ Another shortcut can be to use the Frensel Lens as a screen magnifyer. Fernsel Screen Magnifyers are commercially available, and have been around for years (people used them on TV's since the 70's) My current project is making use of this technique. Rather than deal with the headaches of the dim images resulting from projection, I decided to cut out the middle man, namely, the projection surface. I took an 8.5" x 11" Frensel Lens, and set it into the bottom of a black plastic file box (bought it at Office Depot for about $10 US). After adding a strap to the sides of the open end of the box, I merely attatch the box to the front of my monitor, placing the strap around it's backside (picture a CRT monitor wearing a big halloween mask ;p). This rig will fit most 15"-17" monitors. The Lens itself has 2x magnification, so, the screen appears to be double the original size (15" is now 30"). The magnifyer can also be angled a bit, to further adjust for viewing angle. The monitor I am using for this was mounted on a special boom, so it can be freely adjusted for proper viewing. I am building a new rig around this, using a chair with a head rest to keep the head in an "eyes forward" position. So long as you keep your eyes on the display with magnification, the image fills your FOV, making it pretty immersive. This also works well with my shutterglass system. All that's left are a few tweaks, and a control interface. Most probably going to be a Sidewinder Dual Strike controller, which can be reviewed at the following link: http://www.microsoft.com/products/hardware/sidewinder/devices/DualS/default.htm I have tried this device, and seems perfect for my application. Best of all, it's on sale right now, so I can get it for about $25 US. Overall, Magnification seems to work better for me. Just make sure to use Blackout tape (available at an auto parts store) to seal all the light leaks in the magnifyer. That's the main reason I've found this topic interesting. If anybody want's more detailed info on my project, drop me an e-mail at rave669@usa.net, and I will forward you info in greater detail. Eventually, I'll put up a website on the subject, but I haven't had time to do so just yet ^_^. Currently, the project's hardware status is about 80% complete. -Eric L. | ||
| Anonymous Rating: N/A |
David, you said the image would be upside down, but will it be mirrored or backwards? I'm not sure I understand the project Eric was talking about. You look directly into a 8.5" x 11" Frensel Lens in front of a TV and it will look 30"? | ||
| Eric Lindstrom Rating: N/A |
Pretty much, that's how it works. The actual lens is maybe 8" or so away from the user's face. No eye strain is involved. it works pretty good. And as for the 1st question, yes, the image would be reversed as well. The preferred method of projection from the CRT is off a mirror at a 45° angle, into your lens. The monitor would be on it's back (or face down, depending on your rig) and the mirror is contacting the top-edge of your monitor. Hope this helps, -Eric | ||
| Anonymous Rating: N/A |
I just got my 100" tv plans, but now I am a little confused. It talks about using a magnifying glass 2" in diameter. Which would work better: a 2" magnifying glass or a 8.5" x 11" frensel lens? Thanks! | ||
| Eric Lindstrom Rating: N/A |
Using an 8.5" x 11" frensel lens would work best. using the 2" magnifying glass would work as well, but the image will be fuzzy around the sides of your projected image. Using the Frensel Lens will eliminate this problem. Make sure to keep the case Light-Tight. Every bit of light from your display source will be needed for this to work. -Eric L | ||
| Anonymous Rating: N/A |
So how can I attach the fresnel lens to the case? I was wondering if using 2 fresnel lenses, one in front of the other and spread apart, would make the picture better, worse or no different? Why paint the inside of the case black? Doesn't black absorb the light and wouldn't you want all the light to be reflected out? If I need a mirror as big as the screen(or as big as the fresnel?) how do you make it all fit in a light-tight box? Could you draw a quick diagram in Windows Paint and post it here or e-mail me? Thanks. | ||
| Eric Lindstrom Rating: N/A |
it'll make it worse. Every time a lens is added to your system, your brightness will go down, since each lens will rob some of the light from your display. (read the above posts). one lens, one mirror. really dark case, with no light leaks. use black duct tape, or even better, blackout tape (from an auto parts store or wal-mart) to secure your lens to your case (or focal assembly, whatever) the last thing you want is reflections inside your case (makes the image blurry and messed up) the only light you want getting to the lens is that of your monitor, not the insides of your case, dig? You can make due with a smaller mirror if that's all you have access to, but preferably, you would want a mirror somwhere between the size of your screen and your lens; Bigger is better. optimally, the mirror should be the size of your display's CRT screen. Just make sure your case has no light leaks whatsoever, wheter it's just attached to the front of your CRT, or actually inside your "BOX" so long as no light escapes. turn off all your lights, and if you see light from your tube coming from anywhere besides your lens, it's not light-tight. nuff said. -Eric L. | ||
| David C. Qualman Rating: N/A |
Anonymous, It is really neat to see your interest in building such a project. But, you need to understand that engineers read the books first, and then build the bridge. They don't just go to other bridge builders and ask "What do I do next". The questions about "matte black", inverted images, and plans for a light tight box, all indicate that your eagerness precedes your knowledge. Go to the library and get a high-school, or first year college, physics book. It should explain all of the optics that you need . Then, your questions can be more appropriate for the problem. In fact, then you could be the one that provides some answers to fellow enthusiasts. | ||
| VRJUNKIE Rating: N/A |
David, Excuse me for butting in... but isn't it a little late to tell anonymous to go read a bunch of books and become a amateur physics buff! It was evident from his questions that he was not an optical engineer... you encouraged him by helping him along this far and now drop this hammer on him. I thought that's what this board was for??? -VRJUNKIE | ||
| David C. Qualman Rating: N/A |
Hi VRJ, I absolutely did not want to discourage him. I once was a high-school physics instructor. I taught this level of optics. I see that he has a great interest in this topic, but is getting stymied at every step that he takes. Every question answered generates several more that need to be answered. I am glad to continue answering his questions. But, he really is doing an amateur physics project. He would get much better results, and much better satisfaction, with just a little prep work. I think that my advise to read a little about optics is as valuable as advise about how to affix a light shield to a monitor. I actually do want to hear of his results. I have never built such a device, except for focussing a lamp on the wall with a magnifying lens. | ||
| Anonymous Rating: N/A |
I have a UltraOptix Handi-Lens which is a 8-1/4" x 11" magnifying sheet. I held it up to an old 13" TV, about a foot away. I was able to make out people, even faces, on the wall 8 feet away. There is a picture hanging on the wall and few objects in the way, so I wasn't able to see how the entire picture would look, but it looked encouraging. The room wasn't completely dark because there is a window nearby(it was in the evening) and my 19" CRT was on and facing the same wall. Then I tried holding up the sheet to my CRT I could barely make out windows. It might have had the same picture as the TV because I wasn't trying to read text on the TV, it also could have had something to do with projecting partly on a brown door. I was wondering if it might have something to do with the fact that the sheet was smaller than the screen? If that added to the problem, making a light-tight case around it would probably fix it? The wall I was projecting onto is white and also seems a little glossy. When I actually build the projector and want to use it places without white walls, do you think it would help to spray paint or use some type of gloss on a white sheet? Thank you for all the advice. P.S. You said you held a lens to a lamp and projected the image of the lamp on the wall? I held up my magnifying sheet to a Plasma Ball, and its image was projected on to the wall. It was interesting. | ||
| Eric Lindstrom Rating: N/A |
Finally, some good guesswork! Okay... More info: 1) the bigger the lens, the better. One that is the same size as the screen is optimal. Still, you can probably make due with a smaller lens, one that is as big as the image source (CRT screen) would be the best. anything bigger would work good too, but only within reason, as a huge lens would be expensive and difficult to mount. in fact, you'd be better off using a larger lens to make a screen magnifyer of some sort. BTW, That sheet is not light-tight. A Light-tight case will improve performance like you guessed, the more opaque, the better! Knowing the hurdles of this project, you can try to find ways of making workarounds to those performance-robbing design flaws! Your projection surface is, optimaly, a projection screen. Projection screens have highly reflective crystals embedded in it's surface, letting it reflect light efficiently. using a decent screen will enhance your picture a bit. I have an old movie screen that still works quite well. While still not that bright, my old CRT projector always looked better on that old screen. If you have a screen, use it! if not, use a white wall, or a bleached white bedsheet. glossy white poster board is also a good projection surface. Remember, you want the surface to reflect as much light as possible, get creative (and NO, Mirrors don't work well as viewable projection surfaces, because they are TOO reflective!) -Eric L. | ||
| Anonymous Rating: N/A |
So I would get better results with a 8-1/4" x 11" magnifying sheet and a 13" TV, than I would with a 19" TV and the 8-1/4" x 11" magnifying sheet? "you'd be better off using a larger lens to make a screen magnifier of some sort." Do you mean looking directly into the lens in front of the TV? I've noticed that when looking through the lens at the TV, it almost seems too bright to look at. What about using 4 fresnel lenses? Would that make one large lens or would they each magnify separately? I was wondering how I would change channels with the front end being covered by the lens and facing away from me. I tried using the remote through the lens, and it does work, so hopefully I will be able to put a small mirror at the edge of the screen and it will reflect back to the TV. | ||
| Anonymous Rating: N/A |
I can't tell just by holding my magnifying sheet up to the tv, but does the side of the sheet facing the TV make a difference? One side is smooth and the other is ridged. Thanks. | ||
| David C. Qualman Rating: N/A |
I don't think that the side that you hold up matters. The Fresnel lens is shaped so that overall, it represents half of a convex lens. The optics for this type of lens are symmetrical. One thing that I wanted to point out is that neither the screen or the monitor can be closer than the focal length to the lens. That is, if the focal length is 25", then the monitor must be more than 25" away, and the screen must be more than 25" away. Did you see the inverted image when you focussed the screen on the door? It should have been inverted both top to bottom and left to right. Compounding lenses gets to be pretty tough mathematically. You could simplify the math greatly by using the lens equation to find the image of the monitor through the first lens. Then, use this image as the "monitor" for the second lens. Repeat this through each lens until you find where the final image will be. All you should need are two lenses - one make an image that is inverted, and the second to reinvert the image so that it is right side up. This is like a terrestrial telescope. But, you start to get into really long distances if you have long focal lengths. | ||
| Alexander Oest Rating: N/A |
To Eric You write earlier, that "They also have LCD's which fit into a slide projector" Who are "they"? I've done lots of searches for such a product with no success. It sounds like a cheap soluion for home cinema use. Alex | ||
| Anonymous Rating: N/A |
Yes, the image I projected was inverted both top to bottom and left to right. So I could use another lens instead of a mirror at a 45 degree angle? What type of lens would do this? I read that projecting onto a flat screen can cause the "pincushion effect" where light from the projector travels a shorter distance to reach the middle of the screen than it does to reach the edge of the screen. Since the size of the projected image is determined by the distance to the screen, this makes the image appear slightly larger towards each end. I read this here: http://www.howstuffworks.com/movie-screen1.htm Would it help this type of projector if I figured out a way to curve the sides of the white bedsheet screen? What about a screen made of tin foil or tin foil behind the white bedsheet? | ||
| Eric Lindstrom Rating: N/A |
Arrgh!!! too many questions!!! Head... Hurt.... Okay. anyways, I will attempt to answer some of your questions, in no perticular order: The LCD for the slide projector -This thing is for real. However, I forget the manufacturer. One of my clients has one for product demos. I will find out who makes it for you, and post it here later. You can also make your own from a handheld TV, if the screen is backlit and small enough to fit in the slot of the projector when removed from it's shell. You will need a scan convertor to use a homebrew LCD slide with a PC. some odd infos: -Pincushioning shouldn't be a problem if you are using a frensel lens. if you use a magnifying glass lens, then pincushioning will be a issue. Dont forget, most modern CRT computer monitors can adjust the screen's sidepin setting manually, so you can probably compensate for bad optics with your monitor's sidepin and raster settings! (Read your monitor's documentation for more info on this!) - only use one lens! each lens reduce the amount of projected light that will get to your screen! - To answer questions posted by anonymous, 4 lenses to form a single sheet will project four seperate images. Think of each lens as a camera. you could attempt to focus the four images into one, but it wouldn't make it that much brighter. This could come in handy, however, if you use 3 color monitors, 3 lenses, and 3 colored filters (one RED one BLUE and one GREEN). placing a different filter in front of each CRT, and projecting the 3 colored images on top of one another will produce a brighter image (this is how commercial CRT projectors work) each CRT produces light, essentially making the image that much brighter (save for the light that is robbed by the filters, which is nominal) Also, it would be better to use a 19" TV, since more light is produced by a 19" display than a 13" display. But it all depends on how you apply the knowledge and how good your optics are. A 13" set would definitely be easier to install in a projection case than a 19" set. -On a frensel lens, it is usually best to have the ridges facing TOWARDS the CRT for projection purposes, and OUTWARD for direct viewing applications (screen magnifiers, HMD's, etc) The reason for this is glare; The ridged side of the lens has none, and the smooth side does. glare is bad. This is why the direct view setup I described didn't work well for Anonymous. Try flipping your lens, and don't forget that you can always turn the brightness and contrast down on your monitor to compensate. the added brightness helps in my application, since it serves as a display using shutterglasses, which always make the image darker. The folks at Battletech Center/Virtual World/Disney use a frensel magnifier on their Tesla pods (VR immersion capsule)more info at http://www.virtualworld.com/ -Fun facts: I also have more info on all the original Battletech Center cockpits and hardware/software. I used to be a gold card member, there and VR being a hobby of mine, I've learned a lot about them over the years. Too bad you have to pay bucks to Disney Quest these days to play in them!!! Believe it or not Disney owns something like 80% of the VR related companies out there, and owns a lot of the patents now. If Microsoft is considered a monopoly, then what the hell is Disney supposed to be?!? To believe the advancement of practical VR has been halted by a talking mouse in red shorts. Unbelievable, but true. -Conclusion Now, I am exhausted. Does anybody else have any other questions? I had to have answered everything by now... ^_^ -Eric L. | ||
| Anonymous Rating: N/A |
So a mirror at a 45 degree angle would lose less light than a re-inverting lens and won't make the top or bottom edge of the projected image smaller? | ||
| Eric Lindstrom Rating: N/A |
No. | ||
| Anonymous Rating: N/A |
So I could use a re-inverting lens instead of a mirror and still get the same quality? I was wondering about the mirror at a 45 degree angle. How will the light coming directly from the tv screen affects the light reflecting off th mirror? I drew a small diagram showing how I think the setup would look using a mirror: http://members.tripod.com/~Tylernik/tvprojector.gif The blue line is the lens, and the green line is the mirror. The brown line is the base to hold up the tv. Using a re-inverting lens, it would't have to be upside down and on its back? Thanks | ||
| Eric Lindstrom Rating: N/A |
True. Your diagram is correct. The 2nd lens would be the setup you'd want to use if you wanted to keep the television upright. Try to keep your setup flexible, to leave room for trial and error. It sounds like you know what you are doing now, it's up to you to start building your rig; it sounds like you know what you want out of your setup, and now you know how to accomplish it. Well done, Grasshopper! -Eric L. | ||
| Anonymous Rating: N/A |
Ok, so as soon as I find some blackout tape I can start building it. How strong is blackout tape? Can I un-attach it from the TV when I don't want the projector? Someone told me they didn't believe a mirror would lose the same amount of light as a another lens, but this is true? | ||
| Eric Lindstrom Rating: N/A |
Okay. 1) the adhesive on blackout tape is pretty strong, so for connecting it to your TV, I'd reccommend something less permanant. The best idea would be to use opaque black fabric or plastic to cover any light leaks around the TV screen. Blackout tape is used to recover mouldings on cars, so it's pretty strong. I use blackout tape to hold the case together along it's seams, and hold the lens in as well. 2) your friend was correct, you lose less light with a mirrorr than you do with a seccond lens. -Eric L. | ||
| Anonymous Rating: N/A |
Will the mirror make the entire image narrow or larger at the top than on the bottom? Wouldn't it be better to have a slightly dimmer picture with a second lens than with a warped picture with a mirror? | ||
| Anonymous Rating: N/A |
Is there a way to shorten the distance from the projector to the screen and still have a big picture? | ||
| David C. Qualman Rating: N/A |
The distance from the projecector to the screen and picture size is all in the lens equation (see above) and the magnification equation (also see above). You will probably start with a desired magnification (M), the total distance (d + D), and the focal length (f). Then you could use the equations to come up with some values for d and D that fit your needs. You could also use black electricians tape. It does not stick very strongly, so will not damage your monitor. | ||
| Anonymous Rating: N/A |
I have a 8-1/4" x 11" Hard Page Magnifier lens(unbreakable and scratch resistant). It is a little scratched, and I would like to buy a better one. I'm not sure if I should buy the same kind or a 8-1/2" x 11" which I think would be flimsy? (it doesn't mention being unbreakable and scratch resistant) The hard page magnifier is also more expensive. Eric, you have made one of these projectors? What is the biggest visible image you were able to project? Thanks. | ||
| Alexander Oest Rating: N/A |
An alternative: Overhead projector type setup. Hi everybody. This is a fascinating and long thread, eh? Just thought I'd mention another way of turning a TV (or really, a PC monitor) into a projector. I tried it, but it didn't work. Didn't try very hard, though, and someone with more dedication and better knowledge of optics might be able to make it work. Basically, it was an attempt to switch the box with power supply, bulb and fan on an overhead projector with a monitor. What I did was: I took an old overhead projector, took off the fresnel lens (the one on which you put your transparencies). Took off the arm with the lens and mirror (the one you adjust up and down for focus. Put the fresnel lens on top of a flat trinitron monitor (an old fashioned CRT-one - but with flat screen surface). Turned on the PC and monitor. Tried to position the arm with lens and mirror so that it would catch the image coming from the monitor and transformed by the fresnel lens. Looked at the wall to see if any picture emerged there. It didnt. Possible causes of failure: You place your overhead ON TOP of the fresnel lens. In my case, the lens was on top of the monitor - but I imagined that was only a question of focus. I did nothing to shut out unwanted light. Nothing to ensure that focus was right. The light emitted by a monitor might be way less than the light coming from the bulb of the overhead projector. I didn't try very hard. If someone could make this work, it would be fun. It'd work with shutterglasses. It'd be cheap - old overhead projectors are everywhere. Just an idea... Alex | ||
| Anonymous Rating: N/A |
I think it would be easier and of better quality to just use a tv, light-tight box, frensel lens, and mirror, but where can I get an overhead projector cheap? | ||
| Alexander Oest Rating: N/A |
I'm not sure the overhead projector modification is the best way to go. I just wanted to present it so that somebody with more knowledge in optics had the chance to say that "it'll never work" or "your'e almost there, all that's missing is [some component]". As for getting your hands on an old overhead projector. I asked the department of audiovisual facilities at my university if I could have one. They gave me one with wrecked lightbulb and fan, which was no problem, as these parts had to be thrown away anyway. Larger companies and schools might have old projector wrecks piled up somewhere, too. You might try and ask around. ...remember: a sixpack opens many doors ;-) Alex | ||
| Anonymous Rating: N/A |
Where can I buy higher-quality optics of frensel size? Eric said to try a nature store. Is there a web-site I can go to? Without a case, but with a mirror and my old fresnel lens I have noticed that brightness isn't a problem, it is the sharpness. | ||
| Anonymous Rating: N/A |
How about this: "A high quality, lightweight rectangular (3" x 4") magnifier with a comfortable gray plastic handle." (3X) http://www.shopallenbeys.com/schweiz3xrec.html How would a smaller lens affect the picture? | ||
| Eric Lindstrom Rating: N/A |
The image would be dimmer. The bigger the lens, the brighter and sharper the image. That lens would work on a small LCD screen, or as part of a HMD. Wouldn't work well with a big TV. Maybe a portable TV, however. ^_- -Eric L. | ||
| Anonymous Rating: N/A |
It looks like the TV into projector idea is just a bunch of c&(*&(. I saw a working version of one of these in someone's home several years ago. It included the big lens, the tv, the mirror and the big screen-- a quality realization of the idea. Problem was the tv had to be set very close to the screen-- so close that it got in the way of the picture. And the image was dim and messed up a bit. So I think this idea though good for an optics lesson is a myth in working form. Okay, here's an idea for someone here to make some money. Now the LCD with the projector behind it-- that appears to have promise. So Eric, why don't you put one of these things together with your high tech mind from off the shelf parts-- show us images of the working thing, and we'll all purchase your plans on ebay along with thousands of others. In fact, any of you high tech minds, not just Eric should consider this a challenge-- create a homebrew LCD/projector for at or under $300. Maybe another good challenge would be: create a quality HMD with mouse/look emultation software for gaming at or under $300...maybe a bit harder. | ||
| Anonymous Rating: N/A |
How large was the picture in the version you saw? | ||
| Eric Lindstrom Rating: N/A |
Hehe, I did build an LCD Projector. However, I would never sell the plans, because it should be free, right? Either way, the procedure is simple... I feel another article coming on... =================================================== Building a Homebrew LCD Projector by Eric Lindstrom =================================================== So, you want to get dirty? You ready to break open that old LCD handheld TV and turn it into a projector? Well, in this submission, I will give the knowledge you need to do this. *Disclaimer* I, the writer of this document, willnot be held responsible if you junk your TV in the name of science. Furthermore, I never told you to rip apart your TV in the first place. If you attempt to build this thing, and you fail, it's not my fault. I will not be held responsible for any damage to your equipment. If your friend jumped off a bridge, would you follow him? Thought so! This post is for informational purposes only. Now, let's get started... *IMPORTANT INFO* First off: Do NOT attempt this project unless you: 1) posess knowledge of optics 2) have at least intermediate soldering skills 3) are willing to potentialy turn a working display into a paperweight! This project is by no means easy. If you are hesitant about working with soldering tools or electronics in general, this is NOT a project for you. you WILL get frustrated, and you will also curse your mistakes non-stop. Still interested? Read on! *Parts & tools* What you WILL need: 1 pocket size LCD Television with a backlit display a soldering kit with prescision soldering tools a high-intensity light source and lens assembly. I reccomend using an old slide projector, but an old movie projector will also do. If you are willing, you can build the projection assembly from scratch. *How to do it* First, you have to open the case of the television. Since I don't know which type of TV you are using, the procedure would be difficult to describe in detail, but here's the basic procedure: Remove all screws from the outer case. additional screws MAY secure other internal components. When all the screws have been removed, gently pry apart the shell along it's seam. Be extremely careful not to damage any of the internal connections. A good idea is to power the TV off of batteries, and leave it on as you disassemble the case. If the display goes out, don't panic. check to see that the batteries are making contact still. If you manage to do this, and keep the thing running AFTER the case has been opened, it's time to move to the next step. -Step 2 Switch off the TV and remove the batteries. Now, you must find the actual LCD display. It will usually have some form of backlight behind it. the backlight will either be a flourecent element, or it will be solid-state (like the light-up pinstripes they put on some custom cars, like a glowing white ribbon). Regardless, you have to remove the backlight from the LCD. it may be screwed down, or free-standing. it may also be glued on to the back of the LCD, in which case, you may as well re-assemble the TV, since the backlight must be removed for this project. Remove any fasteners that are still securing the LCD panel to the case. be careful of the ribbon connector that connects the LCD to the main circuit board; You will need this intact. The connection from the mainboard to the LCD is fragile, so bee gentle. once that is done, it's time to proceed. -Extending the display's leash This is the most difficult part of this project. Not all TV's use a ribbon cable, some use wires, or worse, some use very short leads or the LCD is soldered directly to the board. You must map out every lead from the board to the LCD. Get a notebook, and draw a representation if you have to. if you screw up, you're SOL. Now, get a nice spool of wire from Radio shack, the thinnest gague of wire you can find that is insulated. Cut as many individual lengths of wire as there are connections to the LCD. I suggest a lenth of 2', but not much longer. carefully remove the ribbon connector from it's plug on the main board and be sure you remember how it was plugged in (make a note on your worksheet), you should now have the LCD free from the case, with the ribbon connector attached to it. so far, so good. If your display is connected by wires, even better, clip all of them in the middle of each wire, and strip about 1/2 an inch off each cut end. Now, you have to solder each lead to a lenghth of wire. This is to extend the reach of the LCD connector. Bridge the gap between each lead from the end of the connector to it's location on the main board. With the ribbon connectors, you will have to use pad soldering tools to solder the wires to each pad on the end of the connector. You may have to de-solder the connector from the main board to connect the wires to it, but, maybe not. As I have said, it depends on the TV you are using. Be sure to label all your wires with pieces of masking tape to keep your connections straight. Once you have done this, extend the wires outside of the case; I prefer to use the hole left by the vacant LCD, but any method will work. Reassemble the case. you should now have a portable TV, with a 2 foot lead of wires (which should be taped together into a bundle) with the now non-backlit LCD at the other end. if you did this right, and the TV works when it is turned on (hold the LCD up to a light to be sure) then we can move on... -Putting everything into focus Now the fun part. Take your projector. Mount the LCD in the case where the film (or slide) would normally go. make sure the LCD is facing so that, if you were to look into the lens, the image would appear normal (not reversed) yet upside down. Since Backlit LCD's are translucent, and allow light to pass through, the lamp behind the LCD Will act as the light source, the LCD will be like the film in a projector, and the lens will focus the resulting image onto the wall (or screen). The intense heat produced by the lamp may melt your display, so be sure to add a ballast (two sheets of glass on either side of the LCD, each pane of glass should have at least 1/2" between it and the LCD) Adding a fan to circulate the air through the ballast is a good idea too. If you are using an old slide projector, you shouldn't need to do this. Extend the wires outside the projector's case. Now, simply connect the TV tuner to your video source. to connect it to a PC, you will need a SVGA/NTSC scan convertor (UK readers will want to use a PAL scan convertor, others may need a SECAM version. it all depends on where the TV came from). Viola! you are done, you should now have a homebrew LCD projector! Now. I'm sorry if this isn't that detailed, but, as I have stated earlier, it's not an exacting science. each TV out there is different, so there's no way to tell which one you are using. It's always a good idea to read any service manuals for your TV before beginning; it will help. As for MY projector, it died years ago when the tuner crapped out. Still, it's a good project, if you have the know-how. | ||
| Anonymous Rating: N/A |
Thank you, Eric. Some ?s: What was your image quality like? Did you see every pix and how big was the image? Was it dim? Was it worth the time? Also if anyone tries this and finds a specific brand of LCD tv and slide projector that works well, please post here. A hearty thanks to Eric for taking the time to explain that. | ||
| Eric Lindstrom Rating: N/A |
The image was pretty bright, but the larger you make your projected image, the more visible the pixels were. I would suspect this wouldn't be as big a problem nowadays, since the resolution of LCD panels has improved significantly over the years since I built my unit. Projector bulbs are extremely bright, so brightness shouldn't be a problem. I would suggest using dark filters in front of the LCD if the image is too bright. I had about 3 different shades of tinted glass at my disposal for this task. if the image was too bright, I'd simply slip a filter in place of one of the ballast sheets. one of my filters was too dark, however, so I never used it. You could also add a dimmer switch to the lamp assembly in the projector to do this. just install it in-line with one of the power leads going to the lamp. Doing this would give better brightness control over using filters, which are fixed in terms of their brightness value. -Eric L. | ||
| Anonymous Rating: N/A |
I thought someone might do this: here is a pre-built 13" TV converted to 100" TV projector at eBay for $200. http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1221527643 | ||
| Anonymous Rating: N/A |
er...um...it aint prebuilt-- just the plans | ||
| Anonymous Rating: N/A |
It says, "I HAVE CONVERTED THIS 13" TV INTO A 100" BIG SCREEN TV PROJECTOR!! THIS SYSTEM IS READY TO GO! ALL YOU NEED TO DO IS PLUG IT IN LIKE ANY OTHER TV." | ||
| Anonymous Rating: N/A |
It doesn't make any sense. The lens goes for $9withplans and he's selling this 13" tv/lens combo for $300... My point is, that I am skeptical...very skeptical.. It would appear that the item for sale is not for sale at all and would serve as some proof that it existed/could be done so that people would purchase the plans/lens....to attract those looking for a projector. Everyone knows that it can be done... just that it is always a dim picture with the tv too close to the display surface-- that is it can be done but is of little use...and no mention of the negative on his auction-- very skeptical... NO money back offer....tisk tisk... If it works, why isn't there more info on it-- better picture? caveat emptor, eh? | ||
| Anonymous Rating: N/A |
Ok, I'm the same anonymous who started this thread. I've built the projector and I am happy with the results. The picture is approx. 9 feet wide. It is dimmer, but still very visible. The only problem I have with it is getting it focused and keeping it focused. I can find a good position for the slider, but it sometimes falls down. Now that I know it works I want to build a more stable wood case. There are a few light leaks that should be fixed, and I am also using shiny metal screws for handles on the slider which probably interfere with the sharpness a little. I'm also still using my hold scratched fresnel. I have my TV sitting on the floor projecting onto the ceiling(8 feet from the floor). My ceiling has paint ridges which is a little distracting, but I don't know if it interferes with the sharpness that much. As for using this projector for stereo 3-D. I think the sharpness isn't good enough for anaglyph or shutterglasses. So far, what I think looks best on it are cartoons and the news(the close-ups of the reporters at their desk). Thanks to everyone who has shared their information and opinions on this subject. I can take some pictures of the projector if anyone wants to see what it looks like? Christoph, this topic will probably come up again. You should build this yourself and write your own review. | ||
| Anonymous Rating: N/A |
How would a rectangular mirror that enlarges its image affect the picture? | ||
| Anonymous Rating: N/A |
On one level I applaud homebrew efforts-- sincerely-- on another I think about two economic principles-- competitive advantage and opportunity costs. The former dictates that you should stick to doing what you do best and the latter describes the lost resources when you do one thing verses another. I think if you look into the hours that it would take to build one of the devices and research it, it might be more efficient to just work a bit harder at whatever you are good at to earn the $3000 or so needed for an off-the-shelf projector. Don't get me wrong, again I admire the efforts-- but I've been thinking about building some stuff myself and these ideas have come along. I think something more along the lines of an "invention" would be better suited for homebrewers-- something new. | ||
| Anonymous Rating: N/A |
Which would work better to get a 5 ft. picture: a 19" TV with a 8.5" by 11" fresnel or a 13" TV with a 8.5" by 11" fresnel? | ||
| Graham Toal Rating: N/A |
There's one more way of hacking this - although I must point out it is relatively poor quality as you'd expect from the price - but fun for a kid I suspect: use an Artograph projector (one of the < $70 cheapish ones) without the lightbulb, and just place it on top of a small portable TV. Unfortunately the protective plastic in front of most portable TV screens will take the image just a touch behind the plane of best focus, so you may need to strip down your TV a little so that the glass tube is exactly in the focal plane. This unfortunately makes the project a bit dangerous again for kids, so be sure to do it under (intelligent) adult supervision. PS If you're not aware of Artograph projectors, have a look here: http://www.artograph.com/tracer.htm (that's the one I used; maybe a 'tracer jr' at half the price would be OK too) | ||
| Alexander Oest Rating: N/A |
How about rear projection? You could place a monitor, fresnel lens and a rear projection screen in a dark box. Ambient light wouldn't be a problem, and as far as I can calculate, the orientation of the picture would be correct with the monitor turned upside down. With a high gain screen and modest increase in picture area (say a 17" monitor onto a 34" screen), it might be bright enough. I know it's been said that a TV is brighter than a monitor, but one of the basic ideas in my opinion is getting a shutterglasses-capable system. What do you all think? Might it work? Can one buy fresnel lenses that big? | ||
| Nick T Rating: N/A |
Well of course it works. What are you all talking about, buy it and build it and then you'll see you have a $12.95 projection TV. (Poetry unintentional). The problem is you have a $12.95 image too. Well this is a dead horse that I am going to flog one more time just for fun. Let's assume: 1. Watching in total darkness doesn't bother you, or you want to project CNN onto the top of your sensory deprivation tank. 2. You are willing to risk abject depression when you realize you've wasted $50 materials and precious time building that could have been spent in the dark. BTW the plans can be found for free at: http://www.webone.com.au/~caoz/bsbigwoody.htm I get 10% of all profits from the free plans, so buy as many as you can. So don't waste the money on ebay or whatever. 3. You bought yourself a used Lenticular or da-lite or whatever screen with 1.5 gain, or heck even 5 gain. 4. You have cranked the brightness up so far on your CRT that the expected tube life is now measured in minutes. 5. You're comfortable with the fact that now that the heatsinks are on the wrong side of the circuitry, (since the tv is upside-down), you can mask the smell of melting silicon with the Orville Redenbacker you can now pop on the "projector" as you watch your big screen movies . With all that in mind, I was wondering: Does the angle of light as it enters the fresnel lens affect the exit angle? Is there a diminishing return on the size of the source TV? Would a plano convex lens do a better job than fresnel? Do the grooves per inch improve sharpness at a cost of brightness? Is there a source for large amici roof prisms for image correction? (I think it would probably be cheaper to take the set to a repair shop and have the vertical and horizontal switched) Or is there a better method to reverse and invert the image? If you were building one,(and I am since the topic has peaked my interest), what would you change from the above mentioned websites plans? Better Lens? Different Lens? Say you wanted to get a better Lens and a first surface mirror, would you then get a $75 piece of crap instead of a $50 piece of crap? And lastly, does anyone know where to get a listing of ftL, lumens or candle ratings of CRTs? Thanks, Nick | ||
| Greg Kintz Rating: N/A |
For what it's worth, a friend of mine has been using a home brew set close to what's was discribed above for some time now. He has a lens from a now 'long gone' company, and has inverted the image on the set(s). He recently replaced his old 17" set with a new 20" Sony (flat screen) Wega set and the picture doesn't look bad at all. He sticks with a 60 to 65" image, which also helps keep much of the Wega's sharpness intact. | ||
| David Rating: N/A |
I was either going to to wait on the i-glasses svga to come out or go ahead and buy an infocus lp350 dlp projector and a hundred inch screen. Which one do you think would immerse me more into the game? Of course the price difference between the i-glasses svga and projector is around $3000!!! | ||
| Anonymous Rating: N/A |
INVERTING IMAGE. Don't use a mirror on these hombrews. The mirror greatly takes away from the sharpness and brightness, and a TV won't work worth a crap upside-down. Just switch the vertical wires going to the yoke of the TV. There are 4 wires going to the yoke. The vertical wires are almost aways the 2 smaller diameter wires. They are usually brown and grey. Just cut them somewhere in the middle, and switch them (connect one end of the brown wire to the other end of the gray wire and vice-versa). This is a much, much better method than using a mirror. | ||
| Anonymous Rating: N/A |
Hi..interesting discussion.I built one of these gadgets with a 8" frenel lens and a 19" b&w tv about 15 years ago.I had the same problems with brightness.So I gave up on that idea and used it as an "IDIOT-BOX" to project oscilloscope paterns on my wall using an old stereo as a signal source.Hell..I even pluged my guitar synth into it using a chorus effect to generate a difference signal to make cool patterns.I realise this is not 'VR' but this kind of thing does have other uses...If any one is interested i can share how i did it ;-) | ||
| Anonymous Rating: N/A |
How did you do it? | ||
| Anonymous Rating: N/A |
Wow, is this topic even still going?  FWIW, I have a set like was originally posted, a 'commercial conversion' as it were. It has a 13 inch set inside a large wood box (black matte on the inside) sitting upright. (picture is reversed electronically) It projects through two 4 x 6 inch or so frensel lenses onto a 5 foot aluminized screen. Brightness is jacked up on the TV, beyond normal range, but apparently not CRT-destroying range. Brightness of the picture at 5 feet (with the aluminized screen) is actually quite fine with the lights off and the shades drawn during the day. It CAN be watched with the lights on, but the picture is somewhat washed out. I've wanted to replace it with a computer monitor, but I don't know how to reverse the image to leave it upright (as computer monitors dont like being upside down). I pulled the lenses out to play with a computer monitor separately, and i'm not sure of the optics involved but no matter what angle (0, 45, 90 in one or both planes) or where I add a mirror in it's own variety of angles, I can't seem to change the L to R reversal. (maybe having 2 rather than 1 lens?) Insofar as I could view the picture though, the 800x600 text was totally unreadable and 640x480 caused eyestrain, it might have something to do with the pitch of frensel lenses themself, i'm not sure. As I just wandered in from the internet at random and may or may not check this board for followup (assume not), anyone who wants to talk to me further can email me or ask me to come and post more: jasonsteele@NOSPAM.linuxfreemail.com Alternately, if anyone knows how to reverse the picture electronically on the computer monitor without damaging it, please email or let me know if you posted here. Jason Steele | ||
| Anonymous Rating: N/A |
Interesting topic... But I would have thought that with all the knowledge in the posts.. there would have been a few more alternative ideas for creating a brighter picture.... Don't get the Wrong Idea.. I have learned a GREAT deal from the posts...and am Greatful that I "stumbled" across the BBS. Thnaks for the Info | ||
| kick Rating: N/A |
I have read on another message board that folks were having good results with attaching aluminum (tin) foil, shiny side down, into just the focusing box. I used to work for a commericial lighting company and we used "dimpled" thin gauge reflective material in a concave fashion to greatly increase our brightness (or luminence if you will). Has anyone actually used a DVD player to pause a screen image and check the results of matte black interior versus tin foil? I have one group of people swearing that it improves brightness with no decrease in picture quality and others who claim it makes the picture brighter but blurrier (is that a word?). | ||
| Anonymous Rating: N/A |
Hey hey I have just finished my tv projector using a 34cm tv. I used a $180AUD TV. I needed one with RCA inputs and remote. I paid $40AUD to have the image corrected for the projection. I also brought a $15AUD fresnel lens. I have used black felt to line the two boxes. This helps the boxes to slide nicely as well. I made the out side box 15cm longer. When I got the focus perfect I put another piece of cardboard over the front which blocked the whole picture. I then cut a 10cm hole in this piece right in the middle. This has removed all glare from the projection and allowed me to get a larger sharper picture. I was able to watch the Simpsons this evening on a 2.1meter projected image on my wall. I have been smiling ever since. So all up I have spent about $250 Australian dollars. Now my 2 year old to watch the Bear in the HUGE blue house. Fantastic | ||
| Liam Ford Rating: N/A |
for free plans go to... www.DIYprojectionTV.tk | ||
| Anonymous Rating: N/A |
Please, I can use a glass fresnel of a overhead projector (is same to a economic fresnel for projetion), because the pvc an acrilic fresnels are very bad for projection. | ||
| Anonymous Rating: N/A |
Please, I can use a glass fresnel of a overhead projector for the tv projection system? example a dukane 1800 glass fresnel (work same to a economic fresnel for projetion?, +-focus distance, etc), because the pvc an acrilic fresnels are very bad for projection. thanks and Excuse my english. | ||
| Anonymous Rating: N/A |
Brighter monitors!: I found that the new CRT Flat monitors from Samsung (MagicBright) and the new Viewsonic P95F+ (UltraBright). Extracted from samsung PDF: High Brightness Adopting High Gamma Electron Gun, MagicBright™ delivers 330cd/m2 of maximum brightness. Normal CDT monitor has only 150cd/m2, which is less than 1/2 of MagicBright™. http://www.samsungelectronics.com/monitor/flat/index.html What is best for light transmission thru a Fesnel lens, 17" or 19" monitor?. What is the Optimal Fresnel Lens specs for Quality?. Thank you. Jorbedo | ||
| Anonymous Rating: N/A |
I found 2 Fresnel manufacturers: http://www.fresneltech.com/index.html http://display-optics.com/products.htm What is the right specs to place an order?, Bigger size better?, what about grooves per inch?, Foacl Lenghts?. JB | ||
| SLASH! Productions Rating: N/A |
Hello! I am new here, so bear with me, please. I have a gutted 50" projection tv. All that is there is the case, mirror, and fresnel lens. Could I mount a 19" tv where the light lenses would be, reflect that to the mirror, and get a 50" picture on the fresnel? I am hoping to build a big screen tv. Not necessarily a "wall" projection screen, but just have it reflect to the lense itself as it would have done before it was gutted. Could this work? If NOT, can the thick lens from the tv be used in any way to make a projection tv? Thanks! | ||
| Teleport Rating: N/A |
Has anyone tried using 2 Fresnel lenses? 1)One right infront of the CRT acting as a collector so that all the light is directed forward to the second lens and not absorbed by the interior of the enclosure. 2)And the second lense acting in the traditional way as a diverger and magnifying the image onto the screen/wall. I would assume that this arrangement would ensure maximum light efficacy of the setup resulting in a brighter image. The only thing I'm not sure of is how the magnifications of the two lenses would effect the design of the enclosure or the final image. Any ideas? I might try this if noone else has yet. | ||
| Itsikw Rating: N/A |
The lens in front of the CRT will have no effect and is completely useless. The only way to increase the projected image brightness is to increase the size of the imaging lens. Itsik | ||
| Anonymous Rating: N/A |
Hey I got some of those plans and i cant get it to work i mean i can but it is very faint and blurry. | ||
| Anonymous Rating: N/A |
Hey again I got this thing its a 7"x5" magnifying sheet would this work and also i hear sometimes the image would be projected upsidown and backwords, this is confusing! | ||
| Anonymous Rating: N/A |
I found a great projection TV kit which works GREAT! check out this website! http://www.webtv100inch.com | ||
| Anonymous Rating: N/A |
By paying $9.95 to webtv100inch.com you mean they send you some bogus plans of their scam. They sell descrambler plans too that's a definite scam. Tell us exactly what you get for your money and how it works if it's so great or are you the one that profits, not interested in sharing details. | ||
| Peter Rating: N/A |
Hello! Well, here's another "fool". Yepp. me... My son has been bothering me for a time now, asking me if we could build this Fresnel projector thingy. Ok, now is the time to do it. SO check back here in a couple of weeks, cuz you will get the whole story with pictures and all. (Digital camera will be used.) We will try to go for the "smaller" screen, like a 60-100". the "projector will hang in the ceiling and also the screen will. We will use wood, the TV will be standing on the box with it's screen facing down on a mirror (45° angle) and then the fresnel lens will be at the end. Will try both black inside and white/gray. thats it for now, cheers! /Peter | ||
| John Winningham Rating: N/A |
First off, didn't see this link posted: http://www.bstvcentral.b0x.com/ It is free plans. I was bored one night so I decided to experiment. Had an ancient TI computer monitor (accepts phono video input) that has an exceptionally bright color screen. I rigged up a system with a $1 cheap full page fresnel lens (Wal-Mart) and used a large foam panel from a packing container to hold it. Popped an 7" hole in the middle and taped the magnifier to it. Raised the panel up with pillows, boxes, and old computers to get it focused right. Had a decent sized screen on the ceiling. The screen quality was fairly consistant to the pictures shown on ebay but mine was definantly not as big due to limited space between floor and ceiling (no walls free). To watch the TV one would need to be in a pitch black room for a ~10 minutes so as to be able to see the screen well enough. There was some ambient light introduced because of the exceptionally low quality setup, but it was easy to tell about what one could expect from a full setup. I also should add that the monitor didn't smell so spiffy after being faced upwards on full brightness (painfully bright if you look directly at it) for half an hour. ;) | ||
| Anonymous Rating: N/A |
I have a "?" Could you use an old cheap 15in LCD monitor, open it up,(Like the above post with the gutted small TV) put a much brighter backlight behind it and then build it like the "fresnel len's & TV design" ? | ||
| Anonymoose Rating: N/A |
Re: 15" LCD monitor It depends on the LCD. Most LCDs have their boards folded around behind the backlight, and some have the boards on the sides attached to the top or bottom boards with special purpose ribbon cables, so you have to have the boards folded behind the LCD in order to operate it, and that of course will get in the way of any external light source even if the backlight is removed. However, some LCDs don't have this problem - the boards are not attched to one another and an be folded out of the way. My advice would be to use a conventional projection lens of some sort in front of the LCD, and put the Fresnel lens *behind* the LCD, using it concentrate as much light from your lamp as possible into the smaller projection lens. I suspect it will still wind up rather dim, but not as bad as a CRT with a fresnel in front of it. To John Winnningham: It like your test setup - a TV that projects onto the cieling would be great for couch potatoes - there's a product idea in there somewhere. | ||
| Anonymous Rating: N/A |
Thank's for the reply... One more thing I got a fresnel panel (8 1/2 by 11) from office depot and one from office max both where of horrible quality.... Where can you buy a high quality fresnel len's ...maybe made of glass not plastic? I saw the link above but what type do you order? a + fresnel, - fresnel or the collector type? | ||
| anonymoose Rating: N/A |
You can get good plastic Fresnel lenses from Edmund Scientific. You need a positive lens, one that converges light instead of diverges it. You'll need to find someone who knows optics to figure out what focal length you need, given your light source position etc. (or vice versa). There's another possible source of LCDs. Several years ago they used to make LCD "projector pads" that you'd place on an overhead projector to project computer monitor images to classrooms, etc. They were up to about 12" in size and got up to SXGA resolution. I haven't seen one for sale in years, but there must be a lot of cheap used ones around. Obviously, they were all free of obstructions in the back. | ||
| anonymoose Rating: N/A |
Almost forgot - if you can pick up a used overhead projector you'll have all the optics you need - a light source and socket, a Fresnel lens (build into the base), and projection optics. These could be disassembled and then reassembled into a more attractive box. Someone makes cards that let you run TV signals to your monitor through a PC, get one of those and you'll have all you need to watch TV. | ||
| Anonymous Rating: N/A |
for those of you thinking of desmantle 15"tft and project light from behind with overhead projector, see this board; lots of people have done the trick ;) http://www.diyaudio.com/forums/forumdisplay.php?s=&forumid=20 | ||
| Anonymous Rating: N/A |
I bought one here http://www.100inchtv.com and works AMAZING!!! I have a 100 inch home theatre and it cost me only $10 bucks! | ||
| Anonymous Rating: N/A |
Sorry I meant http://www.webtv100inch.com Its ONLY $10 BUCKS! the other website is a ripoff in price! http://www.webtv100inch.com Is the place to go for a 100 inch TV! | ||
| caneta3d Rating: N/A |
I try to pay with paypal but bud is a bad link. Thanks | ||
| Anonymous Rating: N/A |
If you look the schematics are on the web for free. It doesn't work very well. Think about it, you are not amplifying the light from the TV just spreading it wider. If you have a 30inch TV then a 100 inch screen is 9 times the area. The lens itself aborbs some light so the resultant image is a least 10x dimmer. Take into account the surface you project on will also take out some of the light and ....well you get the idea. Don't waste your time or cash. | ||
| Anonymous Rating: N/A |
http://www.diyprojectiontv.8k.com/guide1.html here they are with some pics as well of one finished and the results. I'll eat my words. Not great but not as bad as I would have thought. | ||
| prof.raymond byrnes Rating: N/A |
hi excellent source of data i loved every article...ive been studying this topic for quite a while.yes the frenel tv kits do in fact work however you should only purchase the lense itself.there are many bogus sites out there.be careful.realistically this project will be roughly 20 bucks in materials ad many many hours of science and theory.it is fun however.but as always remember the end result is how much time you have to actually perfect your project..ive built two already.and im becoming quite familiar with this trend.as much as ive learned ..ive also pondered. its allmost like opening pandoras box..be prepared for major to minor stress ,,and also small victories.well enjoy the learning process. | ||
| Anonymous Rating: N/A |
Bought it, tried it, totally disappointed. Completely dark room. White pull down window blind as the screen. Built the box with black tee shirt lined black foam board. No light leaks. adjusted focal length, appature size. The picture was dim and lacked contrast. Here's a Quote from the above mentioned website that sells the Fresnel lens. I've taken the liberty of capitalizing what I think is the most important sentence in the paragraph. "Here are the images I have taken and also collected from various sources on the internet for reasearch purposes. Click each for a full size version in proper aspect as well. NOTE THAT SOME OF THESE IMAGES WERE TAKEN OF LCD PROJECTORS WHICH ARE BUILT SLIGHTLY DIFFERENTLY". Slightly differently?!? That's like saying that a go-cart is slightly different than a Cobra Mustang. If your looking for a big screen for your preteen aged child to watch movies in a completely dark room as a novelty, then go for it. If your thinking about an actual alternative for disconcerning adult movie viewing then you need to look elsewhere. A home built XGA LCD projector for the technically capable will cost you about $500-$1000. A manufactured LCD or DLP XGA solution will run you between $1200-$2000. | ||
| like hobby Rating: N/A |
I found a 5 inch 2x mag. lense AT A YARD SALE FOR 2 BUCKS, USED FREE PLANS that I found on web sites and a 12" x 12" mirror that was hanging around.made screen & painted it with metalic alum.paint & 13" TV . my sceen is 60 inches & awesome picture for a homebrew. Thanks 4 the fun enjoyed reading these postings...... P.S. I am not trying to sell ,just a hobbiest. | ||
| Anonymous Rating: N/A |
Can sou please say the site of FREE PLANS ? vidmax3d@iol.pt | ||
| Anonymous Rating: N/A |
http://www.100inchtv.com | ||
| joe blow Rating: N/A |
yeah it does work, you need to remember to have a lighttight box as well as your room completely dark (wont work in the daytime unless you cover your windows completely lol and the less light bleedthrough from electronic devices the better, the more pitchblack room the better), that is the drawback the room has to be really dark to enjoy, i got a decent pick but i also turned the brightness completely up on my tv, dont turn your tv upside down as it depolarizes some older tvs. I actually made a ceiling projector with a simple cardboard box with a hole in the front and another 2nd box with an open end on the top with the mirror tilted in the second. was ok, definitely would get your ass laughed off if you ever tried to sell it in public, works great with cartoons and black and white movies, reg movies r ok, nothing spectacular. | ||
| Anonymous Rating: N/A |
This topic was done to death on Greenspun forum. It does work, best results i had 8"dia lense from surplus shack mounted in card tube attached to card box around tv screen. Tube slides in and out to focus. To reverse image swop scan coil connects on tube. Use a silver painted screen. | ||
| Traco Rating: N/A |
Has anyone thought about if there is a Auto-Focus HMD? Nowadays, there is only HMD with fixed focal-length. Why dont the others investigate it? Will it be useful? |
