xblocker,
I wasn't doubting what you said earlier--you are correct about some OHP's using spherical reflectors. But what would be the advantage of using a PCX after a bulb/reflector that is already producing diverging light rays? I thought the point of the PCX lens was to take parallel rays produced by a parabolic reflector and then spread them the cover the fresnel. I know that some OHP's use them...I just don't understand why if they are really using spherical reflectors. Can you help me out? And now, onto:
Raiders of the Lost Arc!
Below is an ugly sketch of what I think I understand about the orthogonal reflectors. Please tell me if this is wrong so noboby gets contaminated with my flawed logic 😉 . If the arc is placed in the axis perpendicular to the LCD, the area of the reflector that is actually BEHIND the arc acts as a normal parabolic reflector, with the back edge of the arc as the focal point. At points along the arc, however, the parabolic curvature changes to reflect radial light from the arc in parallel. This curvature continues until the end of the arc, where it resumes a parabolic shape. Is this right??? Maybe?
This would take advantage of the radial light from a long arc, which should be brighter and at least easier to control. In a conventional parabolic or elliptical reflector, much of the light is "wasted" if it is not being produced precisely at the focal point. Since we can't get our hands on a small arc bulb for a reasonable price, maybe this is our best bet?
-f4
I wasn't doubting what you said earlier--you are correct about some OHP's using spherical reflectors. But what would be the advantage of using a PCX after a bulb/reflector that is already producing diverging light rays? I thought the point of the PCX lens was to take parallel rays produced by a parabolic reflector and then spread them the cover the fresnel. I know that some OHP's use them...I just don't understand why if they are really using spherical reflectors. Can you help me out? And now, onto:
Raiders of the Lost Arc!
Below is an ugly sketch of what I think I understand about the orthogonal reflectors. Please tell me if this is wrong so noboby gets contaminated with my flawed logic 😉 . If the arc is placed in the axis perpendicular to the LCD, the area of the reflector that is actually BEHIND the arc acts as a normal parabolic reflector, with the back edge of the arc as the focal point. At points along the arc, however, the parabolic curvature changes to reflect radial light from the arc in parallel. This curvature continues until the end of the arc, where it resumes a parabolic shape. Is this right??? Maybe?
This would take advantage of the radial light from a long arc, which should be brighter and at least easier to control. In a conventional parabolic or elliptical reflector, much of the light is "wasted" if it is not being produced precisely at the focal point. Since we can't get our hands on a small arc bulb for a reasonable price, maybe this is our best bet?
-f4
Attachments
TELL ME!!!!
DID ANYONE IN THIS FORUM ACTUALLY BUILT A WORKING PROJECTOR??????? IF SO< WHAT WAS THE DESIG AND WHO IS THE GUY WHO BUILT IT?????
tell me plz.... aleksey😕 😕 😕 😕
DID ANYONE IN THIS FORUM ACTUALLY BUILT A WORKING PROJECTOR??????? IF SO< WHAT WAS THE DESIG AND WHO IS THE GUY WHO BUILT IT?????
tell me plz.... aleksey😕 😕 😕 😕
Fender4
Not quite right. In your #3 sketch all your parallel rays dont go parallel, they converge to a point to the right of the bulb. See my drawing few days ago.
Not quite right. In your #3 sketch all your parallel rays dont go parallel, they converge to a point to the right of the bulb. See my drawing few days ago.
I found a site that sells metal halide bulbs integrated with an elliptical reflector. They guarantee 1000 lumens focused to a 4mm spot. It comes complete with ballast and cooling solution.
See the LM60 from Welch Allyn:
http://www.walamp.com/FiberOpticIlluminatorsSearch.asp?id=4
CR
See the LM60 from Welch Allyn:
http://www.walamp.com/FiberOpticIlluminatorsSearch.asp?id=4
CR
Got my very first large screen projection today. It is absolutly terrible but I am wrapped. Using elderly low cost slide projector Cabin 1000A with projection lens on. 2 feet away is the lcd panel. Adjust the panel closer/further away until round light from projector just covers LCD panel. Connect panel to video. OK so far. Panel correctly determines I am on PAL TV system. I can see pictures on LCD panel. Slide projector screen placed 5 feet from LCD panel. Picture on screen all blurry. Place page magnifier fresnel at 12 inches in front of LCD. Picture focused now on screen. Picture is terrible but its 6 feet wide and can watch with lights on. Page magnifier is one the cat dragged in. Its wrinkled and wont sit straight and too small to show whole picture.
Took it out.
Experimented with some 50mm dia glass lens in small portion of picture. Best result from magnifying glass shaped lens. Excellent quality can focus pixels quite clearly but they are not obtrusive. Defocus slightly and they disappear. Colour is not special. Seems flat not vibrant colours. Could be the bulb in the slide projector on its last legs. I am scared to pull it out in case it breaks.
Conclusion.
Its great to have a large screen projector.
Panel Infocus Powerview 820. 800x600 and video
Very surprised at what excellent quality light coming out of slide projector. Inside is just like your diagram Xblocker
Light is even right across
Virtually no heat in light at all
Fan is quiet
No discernable blurring on full motion video.
Picture size not very big but still much bigger than my TV.
Page magnifier does a job. Will buy a better one. Has to be size of LCD plus an inch or two. Glass lens do a far better job but chances of getting a 12 inch glass lens could be remote. Only trouble is picture upside down and writting back to front. Fixed the upside down picture by turning the panel down instead of up but writting still reversed. Could need a mirror somewhere unless the panel has reverse switch which I have not seen.
Took it out.
Experimented with some 50mm dia glass lens in small portion of picture. Best result from magnifying glass shaped lens. Excellent quality can focus pixels quite clearly but they are not obtrusive. Defocus slightly and they disappear. Colour is not special. Seems flat not vibrant colours. Could be the bulb in the slide projector on its last legs. I am scared to pull it out in case it breaks.
Conclusion.
Its great to have a large screen projector.
Panel Infocus Powerview 820. 800x600 and video
Very surprised at what excellent quality light coming out of slide projector. Inside is just like your diagram Xblocker
Light is even right across
Virtually no heat in light at all
Fan is quiet
No discernable blurring on full motion video.
Picture size not very big but still much bigger than my TV.
Page magnifier does a job. Will buy a better one. Has to be size of LCD plus an inch or two. Glass lens do a far better job but chances of getting a 12 inch glass lens could be remote. Only trouble is picture upside down and writting back to front. Fixed the upside down picture by turning the panel down instead of up but writting still reversed. Could need a mirror somewhere unless the panel has reverse switch which I have not seen.
Undream
Yes, blocking 1/3 of the lens, will increase sharpness & contras, especially at 4 far-side of the image, try yourself or learn more from the link I gave in previous post and don't forget telling me the result, please.(you use exactly the same lens as mine).
see you.
Yes, blocking 1/3 of the lens, will increase sharpness & contras, especially at 4 far-side of the image, try yourself or learn more from the link I gave in previous post and don't forget telling me the result, please.(you use exactly the same lens as mine).
see you.
PLAS-TEX
well, I figured all this testing on a plain old wall isn't cool enough, so I went and bought a sheet of plas-tex, and $24 worth of lumber. time to build myself a screen. I'll post pictures when I'm done. I got up early this morning to head out to meijer and pick up some liquid nails and black spraypaint for the framing 😉
well, I figured all this testing on a plain old wall isn't cool enough, so I went and bought a sheet of plas-tex, and $24 worth of lumber. time to build myself a screen. I'll post pictures when I'm done. I got up early this morning to head out to meijer and pick up some liquid nails and black spraypaint for the framing 😉
Richard,
as you described your setup, it cannot work! Did you remove the original condensor lenses? They are useless for this panel. Remember: Condensors must not only have at least the size of panels diagonal, they also must have the right focus lenght to match with the image path. You also can completely forget the slide projectors projection lens. Usable should be the lamp and reflector. Concerning panels image orientation, isn't there a setup where you can choose the kind of projection, rear ,front, reverse..?
fender4,
the use of parabolic reflector only makes sense, if it has the at least the size of the panel. A spherical reflector primairly doubles the filament of the bulb for better brightness, that means it makes a real image on filaments plane. A PCX lens in every case converges lightrays, if parallel or not. In OHP the PCX lens pre- converge them before they go to the fresnel, which converges them finally to the projection lens.
Gunawan,
are you working with a single PCX lens as projection lens? If yes, this always will lead to spherical aberations. It's the same in photography. Either small blind and better sharpness, less brightness, or full aperture, less sharpness, more brightness.
Proposal: Go to the next eye glass optical store and ask for 2 used ore slightly damaged eye glasses with focal lenght of about 620 mm. Maybe you get them for nothing. Eye glasses are meniscus lenses. Then fit them together with the convex side outside. Now you have a projection lens which a focal lenght of about 310 mm, which should have better properties than your single lens.
xblocker
as you described your setup, it cannot work! Did you remove the original condensor lenses? They are useless for this panel. Remember: Condensors must not only have at least the size of panels diagonal, they also must have the right focus lenght to match with the image path. You also can completely forget the slide projectors projection lens. Usable should be the lamp and reflector. Concerning panels image orientation, isn't there a setup where you can choose the kind of projection, rear ,front, reverse..?
fender4,
the use of parabolic reflector only makes sense, if it has the at least the size of the panel. A spherical reflector primairly doubles the filament of the bulb for better brightness, that means it makes a real image on filaments plane. A PCX lens in every case converges lightrays, if parallel or not. In OHP the PCX lens pre- converge them before they go to the fresnel, which converges them finally to the projection lens.
Gunawan,
are you working with a single PCX lens as projection lens? If yes, this always will lead to spherical aberations. It's the same in photography. Either small blind and better sharpness, less brightness, or full aperture, less sharpness, more brightness.
Proposal: Go to the next eye glass optical store and ask for 2 used ore slightly damaged eye glasses with focal lenght of about 620 mm. Maybe you get them for nothing. Eye glasses are meniscus lenses. Then fit them together with the convex side outside. Now you have a projection lens which a focal lenght of about 310 mm, which should have better properties than your single lens.
xblocker
lowes
heh, funny story, when I went to get that parkland plastics stuff, I asked someone about it, he said aisle 20, so, I went and searched. After 5 mins, I nearly gave up to go ask him again, and, I finally saw the UPC code on a rack. underneath something else, I found one sheet of the stuff I needed. It was BEAT TO HELL. it had rust marks ALL over it, and scratches up the wazoo. I went back to the guy, and said "Yeah, I found what I'm looking for, but the one you have is all beat up and looks horrible." He said, "Why does it matter? its going underneath something else, right?"
I said "uhh.. Actually I'm going to make a movie screen out of it." He said "ohhkay.. let me see if we have any more". Now, I knew they had more, because when I was at the Lowes in my home town, and I checked for it and they didnt have it, they told me that this other location had 57 sheets of it. So, he started walking down aisles looking up towards the ceiling. Finally, we saw the stuff -- It was BURIED underneath a huge pile of other 4x8sheet flats 15 feet off the ground. The guy muttered something like "The gods are not smiling at me today" and went and got their huge forklift thing. Anyways, 10 minutes later, I had a shiny new sheet of it. Not the top sheet on the flat though, it was way too scratched up.
Laugh, I think he hated me.
heh, funny story, when I went to get that parkland plastics stuff, I asked someone about it, he said aisle 20, so, I went and searched. After 5 mins, I nearly gave up to go ask him again, and, I finally saw the UPC code on a rack. underneath something else, I found one sheet of the stuff I needed. It was BEAT TO HELL. it had rust marks ALL over it, and scratches up the wazoo. I went back to the guy, and said "Yeah, I found what I'm looking for, but the one you have is all beat up and looks horrible." He said, "Why does it matter? its going underneath something else, right?"
I said "uhh.. Actually I'm going to make a movie screen out of it." He said "ohhkay.. let me see if we have any more". Now, I knew they had more, because when I was at the Lowes in my home town, and I checked for it and they didnt have it, they told me that this other location had 57 sheets of it. So, he started walking down aisles looking up towards the ceiling. Finally, we saw the stuff -- It was BURIED underneath a huge pile of other 4x8sheet flats 15 feet off the ground. The guy muttered something like "The gods are not smiling at me today" and went and got their huge forklift thing. Anyways, 10 minutes later, I had a shiny new sheet of it. Not the top sheet on the flat though, it was way too scratched up.
Laugh, I think he hated me.
xblocker
I think that the way the Richard has his setup will work. From how he described it he is using the slide projector as a divergent back light and then using the ferensl to focus. that is why the sides of the picture is being cut off.
I think that the way the Richard has his setup will work. From how he described it he is using the slide projector as a divergent back light and then using the ferensl to focus. that is why the sides of the picture is being cut off.
xblocker
think about it. it is like an ohp with no ferensl and a really big focusing lens.
Draw it out on paper. It looks like it should work.
think about it. it is like an ohp with no ferensl and a really big focusing lens.
Draw it out on paper. It looks like it should work.
remp,
Do not use the fresnel lens in front of the LCD. I asked a friend of mine from JPL who builds space-based telescopes about this, and she said the fresnel lens will not produce a high quality image. Keep the fresnel behind the LCD to use as a condenser lens (but remember that you need two of them unless you are using the double sided OHP type).
CR
Do not use the fresnel lens in front of the LCD. I asked a friend of mine from JPL who builds space-based telescopes about this, and she said the fresnel lens will not produce a high quality image. Keep the fresnel behind the LCD to use as a condenser lens (but remember that you need two of them unless you are using the double sided OHP type).
CR
I was wondering if the following will work. I am using the OHP-style large LCD plan:
source -> condenser lens -> LCD -> projection lens -> screen
Right now I have two $5 page enlargers for the condenser lens (each has a focal length of about 12 inches). I am trying to find out what to use for the projection lens. I want to get 4x magnification on the screen at a distance of 96 inches. I think this means I need to put the LCD 24 inches in front of the projection lens and the focal length should be 19.2 inches (488 mm). The condenser lens has no effect on the magnification; I just need to be sure the LCD is illuminated.
I'm pretty lost here. Please advise.
CR
source -> condenser lens -> LCD -> projection lens -> screen
Right now I have two $5 page enlargers for the condenser lens (each has a focal length of about 12 inches). I am trying to find out what to use for the projection lens. I want to get 4x magnification on the screen at a distance of 96 inches. I think this means I need to put the LCD 24 inches in front of the projection lens and the focal length should be 19.2 inches (488 mm). The condenser lens has no effect on the magnification; I just need to be sure the LCD is illuminated.
I'm pretty lost here. Please advise.
CR
ChuckReese,
1.try focal lenght 12,2" upwards for projection lens, but never use fresnels as projection lens! Look at my advice to Gunawan some posts before.
In case you use 2 fresnels (f=12") together for condensor they add up to focal lenght of 6"(1/fn=1/f1+1/f2).
2. Get them at the LCD at the lamp side. Be shure the distance between lamp and fresnels is little more than 6".
3. Take a sheet of paper and hold it at the other side of panel in a distance about 12". There should now be a spot. In that plane the projection lens has to be adjusted later. You also can try this without the panel.
4. If you're a smoker blow smoke into the lightpath to see it's shape.
5. If the spot on the paper is too large, slightly move the lightsource or the fresnel back and forewards, until smallest otimum is reached. Done!
At the first state don't worry about magnification, be glad if it works!
xblocker
1.try focal lenght 12,2" upwards for projection lens, but never use fresnels as projection lens! Look at my advice to Gunawan some posts before.
In case you use 2 fresnels (f=12") together for condensor they add up to focal lenght of 6"(1/fn=1/f1+1/f2).
2. Get them at the LCD at the lamp side. Be shure the distance between lamp and fresnels is little more than 6".
3. Take a sheet of paper and hold it at the other side of panel in a distance about 12". There should now be a spot. In that plane the projection lens has to be adjusted later. You also can try this without the panel.
4. If you're a smoker blow smoke into the lightpath to see it's shape.
5. If the spot on the paper is too large, slightly move the lightsource or the fresnel back and forewards, until smallest otimum is reached. Done!
At the first state don't worry about magnification, be glad if it works!
xblocker
ChuckReeves,
if you put them together they are like doublesided!
In General: If you have two lenses with a given focal length, you can calculate the common(?) focal lenght with this formula!
xblocker
if you put them together they are like doublesided!
In General: If you have two lenses with a given focal length, you can calculate the common(?) focal lenght with this formula!
xblocker
reflector
Superdave
I was thinking, instead of making your own reflector, why not check the mirror section on www.surplusshed.com
they have a lot of spherical mirrors and the like.
Superdave
I was thinking, instead of making your own reflector, why not check the mirror section on www.surplusshed.com
they have a lot of spherical mirrors and the like.
Panel can reverse video
Richard,
That panel has an option to reverse the video, to correct your backward spelling -
Richard,
That panel has an option to reverse the video, to correct your backward spelling -
xblocker:
My fresnel lenses are page magnifiers so the grating is only on one side. The first lens produces a collimated beam from a point source 12 inches behind it. The second lens takes the collimated beam from the first lens and focuses it to a point 12 inches in front.
I do not see why putting them back to back will result in an effective focal length of 6 inches.
CR
My fresnel lenses are page magnifiers so the grating is only on one side. The first lens produces a collimated beam from a point source 12 inches behind it. The second lens takes the collimated beam from the first lens and focuses it to a point 12 inches in front.
I do not see why putting them back to back will result in an effective focal length of 6 inches.
CR
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