I think that keystone correction when implemented for our diy projectors could solve the problem with too short throw, right? Some companies like NEC have developed special chipsets to do the keystone correction in digital domain. However, what should we do to be able to correct the picture with angled projection? Is it possible by adjusting fresnel or TFT panel or both, and maybe the lens, too?
How about this technology? how does it work?
http://www.proxima.com/support/FAQgeneral.asp
"How does keystone correction work?
Keystone correction works by optically aligning the projector's LCD panel, mirrors and focus lens to produce an upward projection. The alignment or "keystone correction" is typically displayed in degrees (°) of correction."
Seems we have to adjust all of the parts. Life is hard.
Anyway, in this thread there are some instructions how to setup the projector. Also it was suggested that just making the LCD adjustable might be the easiest solution.
The digital correction with Nvidia software propably doesn't either work properly or exist at all..
http://www.proxima.com/support/FAQgeneral.asp
"How does keystone correction work?
Keystone correction works by optically aligning the projector's LCD panel, mirrors and focus lens to produce an upward projection. The alignment or "keystone correction" is typically displayed in degrees (°) of correction."
Seems we have to adjust all of the parts. Life is hard.
Anyway, in this thread there are some instructions how to setup the projector. Also it was suggested that just making the LCD adjustable might be the easiest solution.
The digital correction with Nvidia software propably doesn't either work properly or exist at all..
The easiest way of correcting keystone is by simply lifting or tilting one side of the LCD up or back.
So, could you make a frame for the LCD that could be tilted with a small motor for keystone correction?
Yea, a long time ago I posted something about keystone also...
I was very proud that I had sketches and everything but nobody seemed interested in this subject.. Anywayz: here it is again:
tilting the mirror raises or lowers the image a lot, so it may not be a useful option.
I have an idea... I dont know if it is useful but I'll share my ... "hersenkronkels" (whats that in english?) with you
My keystonecorrection idea uses the method of Scheimpflug. This is a technique which is used in studio-photography with a technical camera (big camera with a lens on a lensplate, a backplate which holds the negative film sheets, and a harmonica-like body in between, the plates can be rotated, tilted and moved). The idea with such a camera is to change the normal depth-of-field plane (which is standing up straight, like the front/back of the camera) so by applying the scheimpflug technique you can make a photograph of an object like a chess board, and have the chess board itself sharp from front to back, unlike normal camera's, where you can only have a sharpness plane on the front or the back (if you know what I mean)
Keystone Correction is also all about the Scheimpflug-Method
What is this Scheimpflug? Well, this is rotating or tilting the lens plate and/or film backplate to adjust the sharpness field location.
When you move only the lens plate, you only adjust the sharpness, when you adjust the film backplate, you adjust the sharpness AND (here's where the keystone thing comes in) the perspective of your object.
For example: a normal cam has parallel plates, so sharpness field is also parallel --> |film |lens |sharpness-field
When your object is _ for example you can do this: |back/lens_sharpness but to change perspective you can do this:
\back|lens/sharpness...
I you look at the fact that maybe you can use this in a projector?? .... maybe ...
ehm... fewww... I dont think I could make my point clear...
I was very proud that I had sketches and everything but nobody seemed interested in this subject.. Anywayz: here it is again:
tilting the mirror raises or lowers the image a lot, so it may not be a useful option.
I have an idea... I dont know if it is useful but I'll share my ... "hersenkronkels" (whats that in english?) with you
My keystonecorrection idea uses the method of Scheimpflug. This is a technique which is used in studio-photography with a technical camera (big camera with a lens on a lensplate, a backplate which holds the negative film sheets, and a harmonica-like body in between, the plates can be rotated, tilted and moved). The idea with such a camera is to change the normal depth-of-field plane (which is standing up straight, like the front/back of the camera) so by applying the scheimpflug technique you can make a photograph of an object like a chess board, and have the chess board itself sharp from front to back, unlike normal camera's, where you can only have a sharpness plane on the front or the back (if you know what I mean)
Keystone Correction is also all about the Scheimpflug-Method
What is this Scheimpflug? Well, this is rotating or tilting the lens plate and/or film backplate to adjust the sharpness field location.
When you move only the lens plate, you only adjust the sharpness, when you adjust the film backplate, you adjust the sharpness AND (here's where the keystone thing comes in) the perspective of your object.
For example: a normal cam has parallel plates, so sharpness field is also parallel --> |film |lens |sharpness-field
When your object is _ for example you can do this: |back/lens_sharpness but to change perspective you can do this:
\back|lens/sharpness...
I you look at the fact that maybe you can use this in a projector?? .... maybe ...
ehm... fewww... I dont think I could make my point clear...
OK, maybe some drawings will clear things up:
I think this Scheimpflug method could be useful when you build your projector according to this... just tilt the LCD display forward, also the lens, but not as much as the LCD... it should be *exactly* the position between the tilt of the LCD and the tilt of the screen (in most cases this is 100% vertical)
the L means lens, the o means object and the b means back of camera (= where film is)
these drawings show what part of the object would be sharp in the photo...
try not to laugh, I'm no Van Gogh... 😉
this last thing leads to controllable perspective-distorting:
1. 2.
3. 4.
1: original image to be projected
2: projected image with keystone distortion
3: image when you use Scheimpflug when you didn't need it
4: image with Scheimpflug method on image which had keystone distortion --> compensated
I think this Scheimpflug method could be useful when you build your projector according to this... just tilt the LCD display forward, also the lens, but not as much as the LCD... it should be *exactly* the position between the tilt of the LCD and the tilt of the screen (in most cases this is 100% vertical)
the L means lens, the o means object and the b means back of camera (= where film is)
these drawings show what part of the object would be sharp in the photo...
try not to laugh, I'm no Van Gogh... 😉
this last thing leads to controllable perspective-distorting:1. 2.
3. 4.
1: original image to be projected
2: projected image with keystone distortion
3: image when you use Scheimpflug when you didn't need it
4: image with Scheimpflug method on image which had keystone distortion --> compensated
Another helpful post I agree with:
LuisGonzalezLT wrote this:
Might be easier to correct for keystoning using a lens stage vertical shift instead of Scheimpflug.
All you need to do is draw an imaginary line from the center of your screen to your light source and then ensure that all of your components are centered on the same line but parallel with each other. This is used heavily in the aforementioned large format view camera to shoot architecture so that the buildings don't 'keystone' toward the top.
Ever take your 35mm SLR camera, point it up at a building, take a picture, and have the building 'keystone', i.e. get much smaller at the top than at the bottom? Using a wide angle lens on that same 35mm point the camera directly at the base of the building but step back far enough so that you can see the top of the building in the viewfinder (but still pointing at the base of the building). The keystoning is gone as long as your film, lens, building are all parallel to each other. In a view camera what you do is make everything parallel with each other but then you have the ability to slide the lens up so that it is in effect pointing up, but without tilting it.
See pic, might help clarify...
LuisGonzalezLT wrote this:
Might be easier to correct for keystoning using a lens stage vertical shift instead of Scheimpflug.
All you need to do is draw an imaginary line from the center of your screen to your light source and then ensure that all of your components are centered on the same line but parallel with each other. This is used heavily in the aforementioned large format view camera to shoot architecture so that the buildings don't 'keystone' toward the top.
Ever take your 35mm SLR camera, point it up at a building, take a picture, and have the building 'keystone', i.e. get much smaller at the top than at the bottom? Using a wide angle lens on that same 35mm point the camera directly at the base of the building but step back far enough so that you can see the top of the building in the viewfinder (but still pointing at the base of the building). The keystoning is gone as long as your film, lens, building are all parallel to each other. In a view camera what you do is make everything parallel with each other but then you have the ability to slide the lens up so that it is in effect pointing up, but without tilting it.
See pic, might help clarify...
declined
ya i get your point but camera lenses are a wider field and the scetch u made wont work to good cos the bending is moving the feild of veiw from the lens away from the lcd, its a good thought though, i recon abit of fooling around ud get it, just one of those things where theroy has to come into practise, im not sure on a 3 lcd setup but id supsect the prisim would be the object that moved but then so would also the rear lcd of the 3, i have seen some pro projectors actually compress an image for a keystone corection basically giving them a higher feild of view on the back of the lens as the image is smaller and u would have less distortion in the image that way but realy as i said fooling around is the key the stone come after when it dont work lol
Trev
ya i get your point but camera lenses are a wider field and the scetch u made wont work to good cos the bending is moving the feild of veiw from the lens away from the lcd, its a good thought though, i recon abit of fooling around ud get it, just one of those things where theroy has to come into practise, im not sure on a 3 lcd setup but id supsect the prisim would be the object that moved but then so would also the rear lcd of the 3, i have seen some pro projectors actually compress an image for a keystone corection basically giving them a higher feild of view on the back of the lens as the image is smaller and u would have less distortion in the image that way but realy as i said fooling around is the key the stone come after when it dont work lol
Trev
declined said:See pic, might help clarify...
Nice pic but where you put the mirror, should it also be tilted and parallel to fresnell / LCD ? I must rebuild my box partly because the software 180 degree rotation with ATI/Omega drivers doesn't work properly with video (it rotates the image but slows down the refresh rate or something, also theater mode doesn't work with rotated image). So I've got chance to do some improvements at the same time (adjustable LCD/fresnel and mirror).
Another idea: if you use the split fresnel / two single fresnels you could adjust the keystone just by tilting the fresnel between the LCD and projection lens.
I haven't made my projector yet, but I don't think that picture you linked to will work mhelin.
I like your second idea better, splitting the fresnel and tilting the 2nd one at an angle should work....
if anyone has tried this I would be interested to know what the maximum angle that can be compensated for is.
I'll be trying for about a 20deg angle of inclination (projector on the floor making a 20deg angle)
I like your second idea better, splitting the fresnel and tilting the 2nd one at an angle should work....
if anyone has tried this I would be interested to know what the maximum angle that can be compensated for is.
I'll be trying for about a 20deg angle of inclination (projector on the floor making a 20deg angle)
hassler
i think 20deg would be about the limit on this as the more u go u will loose some brightness and image shape i would suspect but i could be wrong, i know most pro projectors have about 18deg max from memory from the ones ive seen that is, im sure the crt projectors can get alot more in the keystone than the dlp and lcd projectors but hence a totally different setup.
Trev
i think 20deg would be about the limit on this as the more u go u will loose some brightness and image shape i would suspect but i could be wrong, i know most pro projectors have about 18deg max from memory from the ones ive seen that is, im sure the crt projectors can get alot more in the keystone than the dlp and lcd projectors but hence a totally different setup.
Trev
- Status
- Not open for further replies.