duo, i made it also, but with one 4 inch plano/convex lens, and middle of image is perfect, but edges are blury. where i live you cant find fresnel lens or opaque projector, and that is the reason why i am only convinced, but havent tried things i wrote in last post. if you have 2 page magnifiers or opaque projector, PLEASE try those combinations!
thanks
thanks
the whinner,
I have already done what you ask - I did it with my laptop, a page magnifier, and a 1.5" objective from an old projector.
It only worked if all the lights were out - laptops are dim at best - but I got a really clear image, edge to edge on my wall. I could clearly read all the text from a 1024x768 screen, and there was very little distortion.
Check out the main thread (part II) for some very lively discussions on this topic. If you wish to use a TV, you should really try to get the flattest tube you can - most lenses are designed to project a plane onto another plane. If you try to project a curved surface onto a plane using a normal lens, then the edges WILL be blurry.
You might be able to use a combination of a large fresnel and a Delta IV crt projection lens: they seem to have been optimised for projecting a curved surface.
Alternatively, you might try projecting onto a curved screen...
Good Luck!
Bill.
I have already done what you ask - I did it with my laptop, a page magnifier, and a 1.5" objective from an old projector.
It only worked if all the lights were out - laptops are dim at best - but I got a really clear image, edge to edge on my wall. I could clearly read all the text from a 1024x768 screen, and there was very little distortion.
Check out the main thread (part II) for some very lively discussions on this topic. If you wish to use a TV, you should really try to get the flattest tube you can - most lenses are designed to project a plane onto another plane. If you try to project a curved surface onto a plane using a normal lens, then the edges WILL be blurry.
You might be able to use a combination of a large fresnel and a Delta IV crt projection lens: they seem to have been optimised for projecting a curved surface.
Alternatively, you might try projecting onto a curved screen...
Good Luck!
Bill.
Two lenses
I have a 13" 1 lense projector going on right now. Its alittle dim for my taste though. The edges arent to bad. A flatter screen always helps and so does a curved projector screen to make the lense distance = from center to edges. I found this guy who claims to use two square fresnel lenses to make the image. The box is the same size as the normal DIY tv projectors. But the image is higher contrast and brighter than a single lense. The prob. is that when combining two fresnel lenses both 6x I get 36x. Its huge. My screen is as large as the whole room from a 13" source. Its quite bright but I would like to concentrate the image back down to get it to fit and keep the brightness. I got this by laying the two lenses on top of each other rigid side inwards. This made it so that the lense had to be right against the tv almost. This is prob. why it is brighter? Am I on to somthing or should I give up and go back to one lense. My other idea was to order a fresnel the size of the tv as to gather more light. The current lenses I have are 6x power at 7" x 10" on a 13" tv. I got better edges by sandwhiching the two inbetween two panels of glass as to make them flat. Whats this guys secret with two fresnel lenses? I'm very lost and new to all this. You guys are very smart about imaging and etc. so hopeing for a guiding hand here. Please excuse my total newbe questions I know they must annoy you all. As for backward image prob. I flipped the horizotal on pic tube so it all apears the right way after the lense.
On another matter of brightness I ran across a site about this. They used lcd becasue of the ability to add backlights of great power or by useing a normal backlight type lcd and adding another light source beside the lcd. This makes sense. They commented that a normal tv would also benifit from having the (passive method?) of two bulbs along side the image to brighten it. But the glass on tv would make glare washing out the colours unless you used a filter or anti glare device that is polarized which is expensive (mine was $39.00). I have one for a 15" monitor that I'm going to try, it has the ground wire and anti static, antiglare properties. Would this fit the needs of this? Or is it a wasite of time? Thanks alot for reading this. I'm sure I sound dumb to some of you. But I'm running into alot of dead ends on this and am hopeing some of you really smart people can help me out here. You ever need pc help, just give me a shout-been doing that for a long time. One good turn deserves another I say.
As for lense theory here is what i got, still trying to get what I need out of it for this projector. I'ms ure you guys will understand it way more than I. Please take a looksy-
http://cord.org/cm/leot/course06_mod08/mod06_08.htm
By!😀
I have a 13" 1 lense projector going on right now. Its alittle dim for my taste though. The edges arent to bad. A flatter screen always helps and so does a curved projector screen to make the lense distance = from center to edges. I found this guy who claims to use two square fresnel lenses to make the image. The box is the same size as the normal DIY tv projectors. But the image is higher contrast and brighter than a single lense. The prob. is that when combining two fresnel lenses both 6x I get 36x. Its huge. My screen is as large as the whole room from a 13" source. Its quite bright but I would like to concentrate the image back down to get it to fit and keep the brightness. I got this by laying the two lenses on top of each other rigid side inwards. This made it so that the lense had to be right against the tv almost. This is prob. why it is brighter? Am I on to somthing or should I give up and go back to one lense. My other idea was to order a fresnel the size of the tv as to gather more light. The current lenses I have are 6x power at 7" x 10" on a 13" tv. I got better edges by sandwhiching the two inbetween two panels of glass as to make them flat. Whats this guys secret with two fresnel lenses? I'm very lost and new to all this. You guys are very smart about imaging and etc. so hopeing for a guiding hand here. Please excuse my total newbe questions I know they must annoy you all. As for backward image prob. I flipped the horizotal on pic tube so it all apears the right way after the lense.
On another matter of brightness I ran across a site about this. They used lcd becasue of the ability to add backlights of great power or by useing a normal backlight type lcd and adding another light source beside the lcd. This makes sense. They commented that a normal tv would also benifit from having the (passive method?) of two bulbs along side the image to brighten it. But the glass on tv would make glare washing out the colours unless you used a filter or anti glare device that is polarized which is expensive (mine was $39.00). I have one for a 15" monitor that I'm going to try, it has the ground wire and anti static, antiglare properties. Would this fit the needs of this? Or is it a wasite of time? Thanks alot for reading this. I'm sure I sound dumb to some of you. But I'm running into alot of dead ends on this and am hopeing some of you really smart people can help me out here. You ever need pc help, just give me a shout-been doing that for a long time. One good turn deserves another I say.
As for lense theory here is what i got, still trying to get what I need out of it for this projector. I'ms ure you guys will understand it way more than I. Please take a looksy-
http://cord.org/cm/leot/course06_mod08/mod06_08.htm
By!😀
The winner,
this one can't work properly, cause the CRT is a diffuse light source, which emits light in all directions, not only parallel. So the first fresnel is hit also by lightrays at all angles. This doesn't give a collimated beam for those which are not parallel!
The condition for imaging with a lens is, the lens has to be arranged in a distance between 1 x focal lenght and 2 x focal lenght.
xblocker
this one can't work properly, cause the CRT is a diffuse light source, which emits light in all directions, not only parallel. So the first fresnel is hit also by lightrays at all angles. This doesn't give a collimated beam for those which are not parallel!
The condition for imaging with a lens is, the lens has to be arranged in a distance between 1 x focal lenght and 2 x focal lenght.
xblocker
"cause the CRT is a diffuse light source"
Is this why when using a tv projector of this kind (crt type) you can see light iluminating the room (beyond projected image) even though the tv is in a box and all light must go through the lens. This is prob. why the real good ($3000) crt projectors have only one lens system made up of two or three glass lenses. I know they use more than one as to get around the colour abnormalies from a single glass lens. I've wonderd about that. So even after the lens its still not parallel beams? Kinda scattering about the room?😕 Cause I thought a fresnel made light parallel? O.K. is there a way to undifuse the light as to make the light beams parallel? Is this what fiber optics would do? Lots of questions I know- but I'm learning alot form you guys, thanks.😉
Is this why when using a tv projector of this kind (crt type) you can see light iluminating the room (beyond projected image) even though the tv is in a box and all light must go through the lens. This is prob. why the real good ($3000) crt projectors have only one lens system made up of two or three glass lenses. I know they use more than one as to get around the colour abnormalies from a single glass lens. I've wonderd about that. So even after the lens its still not parallel beams? Kinda scattering about the room?😕 Cause I thought a fresnel made light parallel? O.K. is there a way to undifuse the light as to make the light beams parallel? Is this what fiber optics would do? Lots of questions I know- but I'm learning alot form you guys, thanks.😉
xblocker!
i know that the CRT is a diffuse light source, which emits light in all directions, not only parallel.
but, when i made my first 100inchTV, 4 inch glass lens was picking few non-parallel rays from CRT and projecting them on the wall (with good middle part of image but blurry edges).
what i mean is that you dont have to pick all the light rays in order to get good and bright image!
only parallel rays fresnel would pick up would be suficient to get good image! it would pick up those rays and project them on second lens, and that way you could get much more light then i did with my original concept.
and anoteh thought was that first fresnel would correct problem with edges! back on the greenspun board one guy suggestd to put peace of glass in front of CRT, and to focus lens on the glass, not on CRT. that way lens would project image from FLAT glass instead of COURVED CRT!
first fresnel would do the same thing, and gather more light!
ofcourse, you would have to put lenses in black box, and to put diaphragm (i am not shure how to spell it) - i mean peace of cardboard with small hole in middle of it - between the fresnels. that way only correctly projected rays from first fresnel would hit the second one.
i tried it with two 4 inch glass lenses (i placed peace of cardboard with 4 inch hole and 4 inch lens in the middle of it in front of the screen), and it worked great!
another thought!
i saw 5 inch b&w monitor (1024x768) on the cash register in one shop! if you could find such 5,7 or 9 inch color monitor, you could place those delta lenses directly in front of it and to get the projector!
P.S.: xblocker, i didnt try this 2 fresnel lens configuration becouse i cant find fresnels in yugoslavia! i have friends in stutgart and wienna, could you, PLEASE, find for me some stores where they could buy them and send them to me. i cant find them becouse i dont know german!
THANKS!!!
i know that the CRT is a diffuse light source, which emits light in all directions, not only parallel.
but, when i made my first 100inchTV, 4 inch glass lens was picking few non-parallel rays from CRT and projecting them on the wall (with good middle part of image but blurry edges).
what i mean is that you dont have to pick all the light rays in order to get good and bright image!
only parallel rays fresnel would pick up would be suficient to get good image! it would pick up those rays and project them on second lens, and that way you could get much more light then i did with my original concept.
and anoteh thought was that first fresnel would correct problem with edges! back on the greenspun board one guy suggestd to put peace of glass in front of CRT, and to focus lens on the glass, not on CRT. that way lens would project image from FLAT glass instead of COURVED CRT!
first fresnel would do the same thing, and gather more light!
ofcourse, you would have to put lenses in black box, and to put diaphragm (i am not shure how to spell it) - i mean peace of cardboard with small hole in middle of it - between the fresnels. that way only correctly projected rays from first fresnel would hit the second one.
i tried it with two 4 inch glass lenses (i placed peace of cardboard with 4 inch hole and 4 inch lens in the middle of it in front of the screen), and it worked great!
another thought!
i saw 5 inch b&w monitor (1024x768) on the cash register in one shop! if you could find such 5,7 or 9 inch color monitor, you could place those delta lenses directly in front of it and to get the projector!
P.S.: xblocker, i didnt try this 2 fresnel lens configuration becouse i cant find fresnels in yugoslavia! i have friends in stutgart and wienna, could you, PLEASE, find for me some stores where they could buy them and send them to me. i cant find them becouse i dont know german!
THANKS!!!
the whinner- I tried that combination you showed but with two fresnels. It doesnt work. The best I got was a blurry screen. I put the first fresnel in one end of focus box and then put the hole cut in cardboard piece 12" down the box (this is the focal length of fresenls I have) then the second fresnel at other end of focus box which was 24" long. Seems to be over magnified. But I'm thinking a regular magnifing lens first then fresnel second maybe the right combination. The blurrieness must have somthing to do with how the fresnel is- vs. a magnifying lens. Still not giving up. A tv is very bright compared to a light bulb and there must be some way to use that light. So much is going waisted and this is the problem. A very large fresnel on a 30" tv would prob. be the best, but I cant find a fresnel any larger than a page magnifier yet. If I do I'll be very happy.🙁
Hi Guys,
You don't need parallel rays to project an image through a lens.
In fact, parallel rays only make up a very tiny part of the image - the majority of light that makes up the image is composed of diffuse light, emitted from a single point, that needs to be focused by the lens back into a single point on the image. This is what focussing actually is.
If parallel rays were all that made up the picture, it wouldn't need focussing at all; like the raster scans from a laser beam, the image would be identical if it were projected onto a screen 1' or 100' away.
Check out the lens diagrams on Gunawan's site for details showing just a couple of diverging rays from a light source focussed back into an image for ideas.
Basically, if you are going to project from a diffuse light source, you want the biggest lens you can get, as close to the source as is feasible (Ideally the lens would be bigger than the source, and would be almost flush with it... As in standard CRT projection lenses). This will capture the maximum amount of diverging rays from the source, and focus them into a real image.
The limitations are that for projection, the source must be further away from from the lens than its focal length. The size of the image is based a combination of the focal length, the distance of the source from the lens, and the distance of the image from the lens. (See Gunawan's site for interesting diagrams - I can't draw...)
If you use a fresnel, then there are a number of ways to get the best results. My personal favourite is to put a single fresnel lens about an inch away from an LCD panel. This will capture virtually all the light from the screen and do three things with it:
1) It will beam the diffuse rays from the laptop screen in a fuzzy cone that is narrowest at the focal length of the fresnel;
2) It will magnify the screen;
3) The virtual magnified screen image will be behind the screen itself - as if the screen was further away from an observer than it really is (this is how reading glasses work...)
The end result is that a smaller main projection lens could be used to project the image if it is placed at the apex of the fuzzy cone. The bigger the objective lens, the more light that will be captured and projected.
However, the issue concerning focal length, image size and "zoom factor". The fresnel will restrict placement of the objective due to limitations on the fresnel viewing angle. There will be enough lattitude to focus the image, but zoom will be dicataed by the focal length of the objective. You might need a longer focal length objective if you are going to use a fresnel in magnifier mode...
Bill.
You don't need parallel rays to project an image through a lens.
In fact, parallel rays only make up a very tiny part of the image - the majority of light that makes up the image is composed of diffuse light, emitted from a single point, that needs to be focused by the lens back into a single point on the image. This is what focussing actually is.
If parallel rays were all that made up the picture, it wouldn't need focussing at all; like the raster scans from a laser beam, the image would be identical if it were projected onto a screen 1' or 100' away.
Check out the lens diagrams on Gunawan's site for details showing just a couple of diverging rays from a light source focussed back into an image for ideas.
Basically, if you are going to project from a diffuse light source, you want the biggest lens you can get, as close to the source as is feasible (Ideally the lens would be bigger than the source, and would be almost flush with it... As in standard CRT projection lenses). This will capture the maximum amount of diverging rays from the source, and focus them into a real image.
The limitations are that for projection, the source must be further away from from the lens than its focal length. The size of the image is based a combination of the focal length, the distance of the source from the lens, and the distance of the image from the lens. (See Gunawan's site for interesting diagrams - I can't draw...)
If you use a fresnel, then there are a number of ways to get the best results. My personal favourite is to put a single fresnel lens about an inch away from an LCD panel. This will capture virtually all the light from the screen and do three things with it:
1) It will beam the diffuse rays from the laptop screen in a fuzzy cone that is narrowest at the focal length of the fresnel;
2) It will magnify the screen;
3) The virtual magnified screen image will be behind the screen itself - as if the screen was further away from an observer than it really is (this is how reading glasses work...)
The end result is that a smaller main projection lens could be used to project the image if it is placed at the apex of the fuzzy cone. The bigger the objective lens, the more light that will be captured and projected.
However, the issue concerning focal length, image size and "zoom factor". The fresnel will restrict placement of the objective due to limitations on the fresnel viewing angle. There will be enough lattitude to focus the image, but zoom will be dicataed by the focal length of the objective. You might need a longer focal length objective if you are going to use a fresnel in magnifier mode...
Bill.
Hey I lucked out. I found these two sites that offer very large fresnels even curved for tv viewing!!! One has blue tint suposedly to improve image. So which would work better for a simple tv projector? Blue tint or not. And what size? I'm thinking the smallest at 22" diagnal is enuff. Suggestions before i buy, anyone?
Heres the blue tint, slightly curved to prevent edges from bluring one:
http://www.maxiaids.com/cgi-bin/miv...I&Product_Code=04522&Category_Code=Magnifiers
Here is the other one with money back garuntee:
http://www.edexen.com/spec.html
Not sure of magnification-emailing company now.
Please sugest which one thanks. I'm hopeing it being so large as to gather more light a one lens system maybe enuff!😀
Heres the blue tint, slightly curved to prevent edges from bluring one:
http://www.maxiaids.com/cgi-bin/miv...I&Product_Code=04522&Category_Code=Magnifiers
Here is the other one with money back garuntee:
http://www.edexen.com/spec.html
Not sure of magnification-emailing company now.
Please sugest which one thanks. I'm hopeing it being so large as to gather more light a one lens system maybe enuff!😀
Thy might work as the magnifier that collects the light into a normal objective lens, but beware of relying on them AS an objective lens.
You never know, though...
You never know, though...
tinker!
put the first fresnel in front of CRT and FIX IT there! it is not supposed to move!
put the second one on the box and move it until you get the image!
after that, put the cardboard with a hole in front of the apperature, it will cut off the light that defracted wrong, and it will clear the picture! later you can fix it inside the box, after you determine all the distances!
you can use other lens (glass etc.) instead of second fresnel, but not instead of first one!
look at this as OHP with the CRT instead of glass plate!
and DO NOT use the fresnel from OHP, it is two lenses glued together! fresnel from OHP cant work in 100inchTV!
put the first fresnel in front of CRT and FIX IT there! it is not supposed to move!
put the second one on the box and move it until you get the image!
after that, put the cardboard with a hole in front of the apperature, it will cut off the light that defracted wrong, and it will clear the picture! later you can fix it inside the box, after you determine all the distances!
you can use other lens (glass etc.) instead of second fresnel, but not instead of first one!
look at this as OHP with the CRT instead of glass plate!
and DO NOT use the fresnel from OHP, it is two lenses glued together! fresnel from OHP cant work in 100inchTV!
Attachments
Oh- I see what you mean. But I dont think the page magnifier I have is big enuff to cover the 13" screeen. Still I'll see what I get. Thank you for clearing that up!😀
P.S. So I could use one of those big fresnels I found that are 22" diagnol for $30. for the first lens? And then the page magnifier or a delta like lens unit for the second one right? Thanks.
P.S. So I could use one of those big fresnels I found that are 22" diagnol for $30. for the first lens? And then the page magnifier or a delta like lens unit for the second one right? Thanks.
True, but yet I'd still have to buy the $ bulb and mirrors or a reflector along with useing both fresnels I have and get more lenses for the projection end of it. Also I have been told that crt's have higher contrast then lcd projectors. Thats why the really nice way expensive ones still use a 5" crt inside and not the lcd's, like the $5000 units. THe lcd projectors that are about $3000 are cheaper not better. If I'm wrong please correct me. Besides if this lens doesnt work my other halfs dad has a small 13" tv in living room. HTese lenses I found you look through to the tv so you dont have to turn out the lights. Makes it 22". If it doesnt work for projection I'm gonna give it to him for its regular use. So either way no loss. I might get the 41" for playing games on my 29" tv! That'd be real bright and clear.😀noodles said:
They use three seperate crt tubes of varying sizes depending on how big the projector is. I still love lcd projection but what about using several excatly same model tvs and converging them into one image
Why wouldnt they project well? I thought all fresnels worked the same ruffly. I mean it is just a giant 2x fresnel. Or is that the prob. Confused😕 .Is it actually too big 22" diag.? Any sugestions about why not to use it? thanks.🙂woneill said:
Fresnels are a compromise - they are generally designed to do a specific task - magnification/collimation etc.
Projection is actually very demanding on a lens - the bigger the lens, the more demanding it is. Diverging light rays hitting all parts of the lens from the same point on the source, must be refracted to exactly the same point on the image.
This task is usually beyond fresnels which are only usually good for magnifying a localised area (this is why they are put SO close to the screen).
Bill.
Projection is actually very demanding on a lens - the bigger the lens, the more demanding it is. Diverging light rays hitting all parts of the lens from the same point on the source, must be refracted to exactly the same point on the image.
This task is usually beyond fresnels which are only usually good for magnifying a localised area (this is why they are put SO close to the screen).
Bill.
tinker!
those lenses for tv magnification you found on the web are not fresnels, but plastic lenses. i dont know how will they work for this purpose (focal lenght etc.)!
why dont you buy one 8 x 12 inch page magnifier from staples or apolo?
anyway it is much more cheaper (around 7$) !
and if you have delta lens, could you try it in some shop with those 5 inch monitors for cash register?
those lenses for tv magnification you found on the web are not fresnels, but plastic lenses. i dont know how will they work for this purpose (focal lenght etc.)!
why dont you buy one 8 x 12 inch page magnifier from staples or apolo?
anyway it is much more cheaper (around 7$) !
and if you have delta lens, could you try it in some shop with those 5 inch monitors for cash register?
tinker!
or go to some shop that sells security systems, and try your delta lens with some 5 inch monitor like this one:
http://www.tlc-direct.co.uk/Products/TSSCOUT.html
...just to see if it works!
or go to some shop that sells security systems, and try your delta lens with some 5 inch monitor like this one:
http://www.tlc-direct.co.uk/Products/TSSCOUT.html
...just to see if it works!
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