Oh there not fresnels? O.K. I didnt know that. I already have page magnifiers, they dont make it bright enuff. I have tried both the 13" tv and my 29" tv with them. One thing that confuses me is that the 29" tv is dimmer when used as a projector than a 13". Now it should be brighter but it isnt. Anybody know why? It confuses the heck out of me. Do you think those lenses I showed would work for there real purpose? You know, to just sit in front of tv and look through them. Or will they look funny? Thinking of getting one for my other halfs dad anyhow and not useing it for projection or is it a scam? that 41" one is pretty cool and would work with my 29" tv. Looking like regular tv projection is gonna be near impossible at this point. So I guess its back to lcd hunting again. Still cant find one in the $40 range to experiment with.🙁
I would have to disagree with the whinner. Those lens are fresnel lenses. It doesn't have to be made of glass to be a fresnel. Most page magnifiers are plastic. In essence thats all they are is large page magnifiers that are designed to work with the curved face of the CRT.
Ah, see that was what I was thinking. There are dif. types of plastic they use for fresnels. Also these ones I'm looking at are pvc it says and optical quality, thats higher quality than the page magnifiers plastic is. The curved surface is a good thing as it will make the edges be focused aswell. But I'm a newbe at all this so advice is appreciated as I dont know anyhting for sure. So say if I went for the 41" for my big tv. My question is will it work as they say it will or is there a catch. Like the viewing angles and such are they limited? Do you have to look streight on to them? I think a 41" tv that I wouldnt have to dim the lights to use would be great for playing games and day time use. Then make up a LCD projector for movies and such. What do you think are they a gimmic or do they really work? the 41" one is $90.00 so I would like to find out if its for real before buying one for the big tv. Then if it has pojector like qualities try and get the small one for the little tv. If none knows I'll get the cheapy one first ($30) and see how it goes. Let me know what you think. Hoax or not?🙂
I would actually spend less than $10 on a page magnifier from Staples and see if that works before laying out that much...
If it works, you can buy the bigger lens - and you still have a page magnifier.
If it doesn't work, you still have a page magnifier...🙄
Bill.
If it works, you can buy the bigger lens - and you still have a page magnifier.
If it doesn't work, you still have a page magnifier...🙄
Bill.
I already have a page magnifier. And yes it works, all but not too bright. Trying to get more of the difused light to go throught the lens is the key. How to do it is the question. A little lens just seems to not grab enuff of the light. A tv is very bright but the lens just cant capture it all with a size of 8"x11". These ones are like 22" diagnal at the smallest size. Big, no huge size dif. But theres no way to tell how it will project that light or if it will help a smaller lens gather more from the tv. This is my dillema.🙁
Tinker,
The idea of putting a fresnel in front of a TV to make a larger size picture has been around for years and many claims have been made that you can get up to 100 inch size picture as good as the original.
A lot of this is misinformation because as you make the picture larger you have to accept that the original light from the TV is now being spread out over a larger area therefore you must have a less bright picture until finally you end up with a very very dim picture, but if you set your sights on making say a double size picture you could probably get quite good results. And a good screen will help as well.
Assuming you have a 22 inch TV set and you decided to magnify that picture up to say 48 inches wide you could get a larger picture and it should still be quite watchable but you would need to reduce the background lighting. Also the assumption is that you can succesfully gather and use a good percentage of the TV light output which is a hard thing to do economically so you have to say there will be some losses which means your overall projected brightness will be less than you hoped for. In addition the final quality of your projected image depends on the quality of your fresnels.
But having said all that you are quite correct in that a modern TV set has very good contrast and good colours so a magnified TV picture should be good.
My own TV at home runs at half brightness and contrast and is still pretty bright and we have reading lamps on so if I were doing it your way, I could increase the TV brightness and contrast quite a bit to help get a brighter projected image but that would reduce the TV life somewhat. Depends if you do that all the time or just occasionally.
Slipping a box on your tv (watch for not covering ventilation holes ) and getting a double size or even larger picture is good if you can do it. Isn't the projected picture reversed or upside down. Seem to remember something about that.
If you want to solve your dillema its a good idea to start at square one and read every scrap of info on the internet and in forums about using a TV set with a lens in front to make a bigger picture. From that you should be able to sift out the crap and get an understanding of how these things work. Then when you have the working principle locked firmly in your head you can say Ok now I understand what they are saying and it could work. Or it's just a scam.
Research > knowledge > experimenting > success/failure.
You should be able to try all this out in small scale first using a small TV . Get it working with minimum outlay then see if its worth going up in size. Your labour is free but materials are going to cost you so somewhere along the line you will have to decide if the idea is worth persuing or if you are better off buying a projection panel and an OHP.
The idea of putting a fresnel in front of a TV to make a larger size picture has been around for years and many claims have been made that you can get up to 100 inch size picture as good as the original.
A lot of this is misinformation because as you make the picture larger you have to accept that the original light from the TV is now being spread out over a larger area therefore you must have a less bright picture until finally you end up with a very very dim picture, but if you set your sights on making say a double size picture you could probably get quite good results. And a good screen will help as well.
Assuming you have a 22 inch TV set and you decided to magnify that picture up to say 48 inches wide you could get a larger picture and it should still be quite watchable but you would need to reduce the background lighting. Also the assumption is that you can succesfully gather and use a good percentage of the TV light output which is a hard thing to do economically so you have to say there will be some losses which means your overall projected brightness will be less than you hoped for. In addition the final quality of your projected image depends on the quality of your fresnels.
But having said all that you are quite correct in that a modern TV set has very good contrast and good colours so a magnified TV picture should be good.
My own TV at home runs at half brightness and contrast and is still pretty bright and we have reading lamps on so if I were doing it your way, I could increase the TV brightness and contrast quite a bit to help get a brighter projected image but that would reduce the TV life somewhat. Depends if you do that all the time or just occasionally.
Slipping a box on your tv (watch for not covering ventilation holes ) and getting a double size or even larger picture is good if you can do it. Isn't the projected picture reversed or upside down. Seem to remember something about that.
If you want to solve your dillema its a good idea to start at square one and read every scrap of info on the internet and in forums about using a TV set with a lens in front to make a bigger picture. From that you should be able to sift out the crap and get an understanding of how these things work. Then when you have the working principle locked firmly in your head you can say Ok now I understand what they are saying and it could work. Or it's just a scam.
Research > knowledge > experimenting > success/failure.
You should be able to try all this out in small scale first using a small TV . Get it working with minimum outlay then see if its worth going up in size. Your labour is free but materials are going to cost you so somewhere along the line you will have to decide if the idea is worth persuing or if you are better off buying a projection panel and an OHP.
Thank you remp, all very good points.
"Isn't the projected picture reversed or upside down. Seem to remember something about that."
Yes it is. Its due to how the lens crosses the image over itself at the focal point. This makes the top bottem and so forth. I reversed my yoke horizontal as to flip it upside down before projection and then it appears upright. I have a working 13" model that is about 60" on the screen. At 40" it is brighter. I understand that the further away the more light loss. The thing that gets me is a larger tv should make more light. But I have tried my 29" tv and it seems dimmer for reasons unknown to me. So I know its not a hoax. Just somthing that needs perfecting.
As far as the hoax question I ment the screen enlargers that I posted a link to. They sit infront of the tv and you look into that-you dont project anything so its so bright even when lights are on you can see the image very well. They are tinted slightly blue as to prevent the glare from room lighting disturbing the picture. And the lens is curved slightly to prevent the fish bowl effect. these are what I'm questioning. As in due you have to look streight into them as to see the image correctly. I might just have to get one to find out how they work. Then let you all know what I get from it. As to answer the question "Is it worth $90 to make 29" a 41" tv". The fresnel itself is 41" diag. See if I cant order one this week. Let you all know then how I make out.😉
"Isn't the projected picture reversed or upside down. Seem to remember something about that."
Yes it is. Its due to how the lens crosses the image over itself at the focal point. This makes the top bottem and so forth. I reversed my yoke horizontal as to flip it upside down before projection and then it appears upright. I have a working 13" model that is about 60" on the screen. At 40" it is brighter. I understand that the further away the more light loss. The thing that gets me is a larger tv should make more light. But I have tried my 29" tv and it seems dimmer for reasons unknown to me. So I know its not a hoax. Just somthing that needs perfecting.
As far as the hoax question I ment the screen enlargers that I posted a link to. They sit infront of the tv and you look into that-you dont project anything so its so bright even when lights are on you can see the image very well. They are tinted slightly blue as to prevent the glare from room lighting disturbing the picture. And the lens is curved slightly to prevent the fish bowl effect. these are what I'm questioning. As in due you have to look streight into them as to see the image correctly. I might just have to get one to find out how they work. Then let you all know what I get from it. As to answer the question "Is it worth $90 to make 29" a 41" tv". The fresnel itself is 41" diag. See if I cant order one this week. Let you all know then how I make out.😉
tinker!
have you tried that setup with two fresnels and 13 inch tv?
did you turned bumpy side of the first fresnel towards the tv, and the second opposite?
what are the results?
have you tried that setup with two fresnels and 13 inch tv?
did you turned bumpy side of the first fresnel towards the tv, and the second opposite?
what are the results?
Brighter but blurier at edges. Colors are alot brighter. Cant figure why the focas prob though. Am I missing somthing? Maybe if the first lens is larger and beter quality-then the edges will be clear cause the projected image will be coming from a flater panel of larger lens already having the light gathered from the tv. Wouldnt this make it easier for the second lens to get all the light or will the light still be difused?😕
tinker
did you use that cardboard with a hole to cut off wrongly dispersed light?
also try to move second lens and see if you can focus only edges, regardless of middle of the screen, just to see is the problem in the courvature of the screen!
just as in OHP, first lens in 100inchTV has to be equal or larger than the CRT, and the second lens can be smaller!
did you use that cardboard with a hole to cut off wrongly dispersed light?
also try to move second lens and see if you can focus only edges, regardless of middle of the screen, just to see is the problem in the courvature of the screen!
just as in OHP, first lens in 100inchTV has to be equal or larger than the CRT, and the second lens can be smaller!
I dont think my first one is big enuff. Going to have to get that 22" one. Then I'll try again. Yes I did try the hole deal, but I think your right, my first fresnel isnt large enuff.🙂
the problem... I want a bigger t.v. Oh say 100". I have a CRT. 19" at best. question- how to make the picture bigger? You guys do wonders with your knowledge of lens systems and ideas. Optics, lenses, if you were all working for trinatron the other competitors would be out of business. but I will answer your ultimate question. How do I get a better picture with this 100" tv idea?
Answer- It is good you can improve picture quality with your knowledge of optics. but what you all should be focusing on HOW TO MAKE A CRT BRIGHTER!!! more lumens people... there is no way to get good quality with a tv as a imager when it puts out 2 lumens! no matter what set up you use you will only improve it by a minimum.
Answer- It is good you can improve picture quality with your knowledge of optics. but what you all should be focusing on HOW TO MAKE A CRT BRIGHTER!!! more lumens people... there is no way to get good quality with a tv as a imager when it puts out 2 lumens! no matter what set up you use you will only improve it by a minimum.
" there is no way to get good quality with a tv as a imager when it puts out 2 lumens! no matter what set up you use you will only improve it by a minimum."
I agree, I have come to this point myself. What is the lumen output of a standard tv? Anyone really know? But yes it is very dim to say the least. And through my experiments I have found that a larger say 29" tv is no brighter than a 13" tv. Reason. Well its a larger bulb (tube) not a brighter one. So you get a larger image projected not a brighter one at all. Now a 13" and a 29" tv both projecting a size of say 4'. Then 29" will be clearer and more defined as it isnt enlargening the pixels so much through magnification but the lumens output is ruffly the same. I'm afraid these tv's are just too dim. And if you brighten the pic too much it whitens out the colors (I've tried!). Think for now its a dead end folks.🙁 LCD seems the only way or a real crt projector-ohh I only wish. Can someone float me about $6000-$10,000 hehe.😀
I agree, I have come to this point myself. What is the lumen output of a standard tv? Anyone really know? But yes it is very dim to say the least. And through my experiments I have found that a larger say 29" tv is no brighter than a 13" tv. Reason. Well its a larger bulb (tube) not a brighter one. So you get a larger image projected not a brighter one at all. Now a 13" and a 29" tv both projecting a size of say 4'. Then 29" will be clearer and more defined as it isnt enlargening the pixels so much through magnification but the lumens output is ruffly the same. I'm afraid these tv's are just too dim. And if you brighten the pic too much it whitens out the colors (I've tried!). Think for now its a dead end folks.🙁 LCD seems the only way or a real crt projector-ohh I only wish. Can someone float me about $6000-$10,000 hehe.😀
Tinker
Dissapointing isn't it that one cannot simply put a lens system in front of an ordinary TV and get a larger picture on the wall. People have been experimenting with this for many years but the fundamental problem is exactly as you have found. There is not enough light coming off a TV to be usable. And there are problems trying to capture the light that is available.
But if you really want a large picture it is available. A very simple solution is buying a used projection panel and putting it on top of an overhead projector and there you are. Large screen projection for $250 - $350.
The results you get depend on the quality of the panel and how bright the OHP is but 48 inch picture width size is easily obtained even with low cost gear.
The guys in the video projector threads are experimenting with brighter light sources to make larger pictures and better panels and computer control to make the final image better but still at lowish cost.
Dissapointing isn't it that one cannot simply put a lens system in front of an ordinary TV and get a larger picture on the wall. People have been experimenting with this for many years but the fundamental problem is exactly as you have found. There is not enough light coming off a TV to be usable. And there are problems trying to capture the light that is available.
But if you really want a large picture it is available. A very simple solution is buying a used projection panel and putting it on top of an overhead projector and there you are. Large screen projection for $250 - $350.
The results you get depend on the quality of the panel and how bright the OHP is but 48 inch picture width size is easily obtained even with low cost gear.
The guys in the video projector threads are experimenting with brighter light sources to make larger pictures and better panels and computer control to make the final image better but still at lowish cost.
Hi remp,
When i did my first CRT projection experiments long time ago, i had the idea, that the cruxical point was the light diffusion of the CRT, not it's brightness in general. Every light emitting phosphor point(pixel) gives his light into all directions and only the light that hits the objective is used for projection. So if each pixel had it's own prism (lens) and bring light to projection lens, then all the light could be used. That would mean, if a layer of prisms (lenses) would be integrated on top of the phosphor, there could be a increase of brightness proportional to the now wasted light! Of course this is nothing for DIYers, and i never saw such plans in the industry.
xblocker
When i did my first CRT projection experiments long time ago, i had the idea, that the cruxical point was the light diffusion of the CRT, not it's brightness in general. Every light emitting phosphor point(pixel) gives his light into all directions and only the light that hits the objective is used for projection. So if each pixel had it's own prism (lens) and bring light to projection lens, then all the light could be used. That would mean, if a layer of prisms (lenses) would be integrated on top of the phosphor, there could be a increase of brightness proportional to the now wasted light! Of course this is nothing for DIYers, and i never saw such plans in the industry.
xblocker
"But if you really want a large picture it is available. A very simple solution is buying a used projection panel and putting it on top of an overhead projector and there you are. Large screen projection for $250 - $350. "
Or even less. But the DIY projector route (i.e. not a OHP). That is what I'm doing now. Had to face it I guess. I got a 5.6" active matrix TFT psone panel rca input for dvd/vcr for $50. Gonna start with that and about 200-250watts for a 4' image. From there once I get a feel for what I'm doing I'm getting a 8-10" OHP setup and about a 8' image. 😀
Why not too big. Well it seems alot easier to get the smaller projection, and also need alot less expensive bulbs and less heat. The bulbs are also smaller. So 4' for now seems to be the most easy to acomplish-right?😕 On that note, is say 4 bulbs better than one, as to make the edges brighter? I know you guys tried leds but I mean like MH bulbs or whatever.
Or even less. But the DIY projector route (i.e. not a OHP). That is what I'm doing now. Had to face it I guess. I got a 5.6" active matrix TFT psone panel rca input for dvd/vcr for $50. Gonna start with that and about 200-250watts for a 4' image. From there once I get a feel for what I'm doing I'm getting a 8-10" OHP setup and about a 8' image. 😀
Why not too big. Well it seems alot easier to get the smaller projection, and also need alot less expensive bulbs and less heat. The bulbs are also smaller. So 4' for now seems to be the most easy to acomplish-right?😕 On that note, is say 4 bulbs better than one, as to make the edges brighter? I know you guys tried leds but I mean like MH bulbs or whatever.
Greetings Xblocker
What you say is the critical point. All the light from a TV front face is hard to collect because it goes everywhere. If you sit right around at nearly 90 degrees to the front you can still see the TV. Maybe not quite so good as at a smaller angle. So if there was some way to gather the light that is going in all directions and point it forwards the whole situation could change a great deal.
The only thing I have seen that could work is a Micro Lens Array . MLA. This is a lot of very very small lens packaged on a flexible sheet. It could make a big difference but you still have a lot of wasted light because the glass front on a Tv is between 6mm to 25mm depending on the picture tube size. You need to get the MLA collector as close to the phosphour pixels as possible before the light has a chance to spread out. Thats not easy with thick glass front in the way. Maybe thats why Tinkers experiments showed not much difference with the size of the TV. Too much glass on the big TV. ??
I tried just putting an ordinary magnifying glass in front of the TV. Sure enough the small section of TV behind the magnifying glass was a lot bigger still with good colour. It got so big I could see the colour triad dots easily. Thats what magnifying glasses do but it's not the same as amplifying the picture onto a wall or screen.
Here is a link to a MLA supplier. They go up to 12 inch square so they say.
http://www.aoainc.com/
The trouble is someone has to buy an MLA sheet and test it.
Unless the manufacturer is prepared to offer a sample for free or very low cost. Even a small piece of MLA say 2 inches square should be enough to see if there is any better light collection.
What you say is the critical point. All the light from a TV front face is hard to collect because it goes everywhere. If you sit right around at nearly 90 degrees to the front you can still see the TV. Maybe not quite so good as at a smaller angle. So if there was some way to gather the light that is going in all directions and point it forwards the whole situation could change a great deal.
The only thing I have seen that could work is a Micro Lens Array . MLA. This is a lot of very very small lens packaged on a flexible sheet. It could make a big difference but you still have a lot of wasted light because the glass front on a Tv is between 6mm to 25mm depending on the picture tube size. You need to get the MLA collector as close to the phosphour pixels as possible before the light has a chance to spread out. Thats not easy with thick glass front in the way. Maybe thats why Tinkers experiments showed not much difference with the size of the TV. Too much glass on the big TV. ??
I tried just putting an ordinary magnifying glass in front of the TV. Sure enough the small section of TV behind the magnifying glass was a lot bigger still with good colour. It got so big I could see the colour triad dots easily. Thats what magnifying glasses do but it's not the same as amplifying the picture onto a wall or screen.
Here is a link to a MLA supplier. They go up to 12 inch square so they say.
http://www.aoainc.com/
The trouble is someone has to buy an MLA sheet and test it.
Unless the manufacturer is prepared to offer a sample for free or very low cost. Even a small piece of MLA say 2 inches square should be enough to see if there is any better light collection.
Hi remp,
i don't believe the MLA should work outside of the tube. It should sit directly on the phosphor, no other glass between. But that would mean, a special production of tubes only for this purpose. Also MLA must be arranged that way, that the pixel's light from outer edges has to be directed more to optical axis then center pixels. Probably it's not very realistic to ever get such a thing.
Have you already heard of the 'Brightness Enhancement Film' from 3M? They claim to make an image brighter by directing diffuse light to the viewer. It's already used for LCD panels to increase overall brightness. But i don't know much about it.
greetings
xblocker
i don't believe the MLA should work outside of the tube. It should sit directly on the phosphor, no other glass between. But that would mean, a special production of tubes only for this purpose. Also MLA must be arranged that way, that the pixel's light from outer edges has to be directed more to optical axis then center pixels. Probably it's not very realistic to ever get such a thing.
Have you already heard of the 'Brightness Enhancement Film' from 3M? They claim to make an image brighter by directing diffuse light to the viewer. It's already used for LCD panels to increase overall brightness. But i don't know much about it.
greetings
xblocker
Greetings Xblocker,
No I have never heard of that film. Could be useful.
This problem of gathering light from a TV is not a new one and it has been solved. You remember CRT projectors. They gather all the light from 3 CRT units and project it on the wall.
CRT projection units take the light output from a small source EG specially built powerful extremely bright 5 inch CRT and can deliver a large projected image at quite high brightness. By using 3 light sources instead of just one there is sufficient projected light for good colour results.
No I have never heard of that film. Could be useful.
This problem of gathering light from a TV is not a new one and it has been solved. You remember CRT projectors. They gather all the light from 3 CRT units and project it on the wall.
CRT projection units take the light output from a small source EG specially built powerful extremely bright 5 inch CRT and can deliver a large projected image at quite high brightness. By using 3 light sources instead of just one there is sufficient projected light for good colour results.
Hi Remp, Xblocker,
I may be missing something here, but I don't think MLAs are necessary in this context - what Xblocker was describing above with his array of prisms sounded very much like a fresnel lens being used to direct the diffuse light from a tv screen into a diffuse cone that can be focussed by the objective lens...
In this scenario, diffuse light is not bad - it is fundamental to the way lenses project an image:- they take the multiple rays of light from a point on the screen, and cause them to converge back to a single point on the image.
Fresnels are crap at doing that, but if they are used merely to "divert" the difuse rays a little so that they are "diffusing" 😉 towards the objective, the objective gets much more light to focus into an image than it would do if the fresnel weren't there and the objective was only using the light that diffused its way by chance...
If the fresnel is close to the screen, each point on the fresnel is only bending the light from a small area on the screen, and there is not as much distortion as there would be if it were being used for actual projection...
Of course, with CRT projectors, the projection lens is bigger than the area of the screen being projected - then there is no need for a fresnel.
Bill.
I may be missing something here, but I don't think MLAs are necessary in this context - what Xblocker was describing above with his array of prisms sounded very much like a fresnel lens being used to direct the diffuse light from a tv screen into a diffuse cone that can be focussed by the objective lens...
In this scenario, diffuse light is not bad - it is fundamental to the way lenses project an image:- they take the multiple rays of light from a point on the screen, and cause them to converge back to a single point on the image.
Fresnels are crap at doing that, but if they are used merely to "divert" the difuse rays a little so that they are "diffusing" 😉 towards the objective, the objective gets much more light to focus into an image than it would do if the fresnel weren't there and the objective was only using the light that diffused its way by chance...
If the fresnel is close to the screen, each point on the fresnel is only bending the light from a small area on the screen, and there is not as much distortion as there would be if it were being used for actual projection...
Of course, with CRT projectors, the projection lens is bigger than the area of the screen being projected - then there is no need for a fresnel.
Bill.
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