I know its an obvious question but is your projector square on to your screen.
There was a similar problem a while ago and it turned the guy was using a projection lens that had keystone correction built in but he did not know that at the time. A new lens fixed it.
There was a similar problem a while ago and it turned the guy was using a projection lens that had keystone correction built in but he did not know that at the time. A new lens fixed it.
I will be working on similar set up (MH + ellipsoidal etc) and am looking for info on condenser lense. Can you post details about the condenser lense and where did you buy it from? A picture will be nice if possible.
Thanks in advance.
Thanks in advance.
Keystone Correction
Remp: Is there any way to determine if a condeser lens had keystone correction build in??
Rajkumar: I purchased the lens from surplus shed and it looks exactly like the one here http://www.surplusshed.com/search.cfm
Remp: Is there any way to determine if a condeser lens had keystone correction build in??
Rajkumar: I purchased the lens from surplus shed and it looks exactly like the one here http://www.surplusshed.com/search.cfm
Not by looking at it. You could remove it to see if any better. They dont put keystone correction into condensor lens, just the projection lens. And only a very few of those had keystone correction. Picture theatre projection lens have keystone correction. You said you adjusted the position of the condensor lens but the keystoning is still there. That sort of proves its not the condensor lens
This keystoning comes about by the usual arrangement of having the projector on a lowish bench or table and projectiong uphill onto a screen that was usually higher. Or the other way around.
I have keystoning at home. The projector is mounted on a rather nice tea trolley and I wheel it into position. The OHP has a lift up mirror. When that mirror is at 45 degree angle there is no keystoning but the picture is half way off the screen at the top. So I tilt the mirror down a very very small amount. Picture now fills the screen but there is noticable keystoning.
Soon I will be lifting the screen up a foot or two into its correct position. and I expect my keystoning to disappear.
Its amazing how much error one can get by just a very small amount of "off center" optics alignment.
If you have exhausted all other possibilities and asssuming your gear is on the optical center line, and your projector is square on to the screen in both directions, (left/right and up/down) you can put in your own anti keystoning by tipping your lcd panel a very small amount. I did this for a friend about a year ago and it is a very fiddly job. So you got an idea, tipping means no more that somewhee between a 1/16 and 1/8 of an inch. Not very much
Any more than that and you will loose focus over the screen area. Come to think of it you did mention you had that problem.
This keystoning comes about by the usual arrangement of having the projector on a lowish bench or table and projectiong uphill onto a screen that was usually higher. Or the other way around.
I have keystoning at home. The projector is mounted on a rather nice tea trolley and I wheel it into position. The OHP has a lift up mirror. When that mirror is at 45 degree angle there is no keystoning but the picture is half way off the screen at the top. So I tilt the mirror down a very very small amount. Picture now fills the screen but there is noticable keystoning.
Soon I will be lifting the screen up a foot or two into its correct position. and I expect my keystoning to disappear.
Its amazing how much error one can get by just a very small amount of "off center" optics alignment.
If you have exhausted all other possibilities and asssuming your gear is on the optical center line, and your projector is square on to the screen in both directions, (left/right and up/down) you can put in your own anti keystoning by tipping your lcd panel a very small amount. I did this for a friend about a year ago and it is a very fiddly job. So you got an idea, tipping means no more that somewhee between a 1/16 and 1/8 of an inch. Not very much
Any more than that and you will loose focus over the screen area. Come to think of it you did mention you had that problem.
Actually...
I have exactly the same problem as you do. When the mirror is at its fully range (45 degrees) the image is off the top of the screen, I angled it down to solve this problem but was'nt aware that this is what would cause the keystoning. Problem identified hurrayyy!!! Now, is there any way of correcting this besides tilting the panel or getting higher ceilings in my house???
I have exactly the same problem as you do. When the mirror is at its fully range (45 degrees) the image is off the top of the screen, I angled it down to solve this problem but was'nt aware that this is what would cause the keystoning. Problem identified hurrayyy!!! Now, is there any way of correcting this besides tilting the panel or getting higher ceilings in my house???
Bitbyter
Hey man I am really pleased that helped you out. Made my day.
The usual thing is to put the house on hydraulic rams. Leave the projector standing on a box or something and raise or lower the house until its perfect.
Sounds like your projector could be a tad too high. I have to raise my screen which I can do, but sounds like you cannot. Only alternative is lower the projector. For the whole thing to be perfect you need the centre of the screen to be in line with your projection lens. Not only that but the face of the projection lens should be parallel to your screen
like this !....!
Not like this /......!
This means your projector has the best seat in the house so they are trying to get around this with software keystone correction
Hey man I am really pleased that helped you out. Made my day.
The usual thing is to put the house on hydraulic rams. Leave the projector standing on a box or something and raise or lower the house until its perfect.
Sounds like your projector could be a tad too high. I have to raise my screen which I can do, but sounds like you cannot. Only alternative is lower the projector. For the whole thing to be perfect you need the centre of the screen to be in line with your projection lens. Not only that but the face of the projection lens should be parallel to your screen
like this !....!
Not like this /......!
This means your projector has the best seat in the house so they are trying to get around this with software keystone correction
Unfortunately I have built a verticel design, so lowering the projector will be just as big a problem as raising the roof 
Well, I guess I have discovered one of the potential design restrictions of the verticle design. I have one more possible solution to try before defaulting to software keystone correction but I doubt it will work. If the software does the job well then I will be satisfied.
ON a side note, does anyone have any direct experience comparing brightness levels between having your lcd right on the fresnel as compared to an inch or so above it??
I'm still looking for any possible edge in the brightness department. Mind you I still have to check my condensor lens's position because if missaligned I believe I could be missing out on a lot of light potential.
Well, I guess I have discovered one of the potential design restrictions of the verticle design. I have one more possible solution to try before defaulting to software keystone correction but I doubt it will work. If the software does the job well then I will be satisfied. ON a side note, does anyone have any direct experience comparing brightness levels between having your lcd right on the fresnel as compared to an inch or so above it??
I'm still looking for any possible edge in the brightness department. Mind you I still have to check my condensor lens's position because if missaligned I believe I could be missing out on a lot of light potential.
Pictures
I hope to have some pictures available by next weekend. Basically I have a bottom platform right on the ground that all the electronics are attached to. I am using a 400W MH grow light and reflector, so the bottom portion is pretty big (reflector is 16" wide and about 12" high). I had a sheet metal shop custom build a cover for my reflector which holds the condensor lens but may be modifying this shortly as I do not think I have it at the F2 point. Above this is the Fresnel lens with my LCD panel sitting right on top. Finally I have the lens assembly from one of my 3M 9700 OHP. OVerall the platforms are round and held up by 4 threaded rods. The whole thing will eventually be covered in a Sonotube and decorated with movie posters. Not small by any means but it actually doesn't take up that much room because of the vertical design.
I hope to have some pictures available by next weekend. Basically I have a bottom platform right on the ground that all the electronics are attached to. I am using a 400W MH grow light and reflector, so the bottom portion is pretty big (reflector is 16" wide and about 12" high). I had a sheet metal shop custom build a cover for my reflector which holds the condensor lens but may be modifying this shortly as I do not think I have it at the F2 point. Above this is the Fresnel lens with my LCD panel sitting right on top. Finally I have the lens assembly from one of my 3M 9700 OHP. OVerall the platforms are round and held up by 4 threaded rods. The whole thing will eventually be covered in a Sonotube and decorated with movie posters. Not small by any means but it actually doesn't take up that much room because of the vertical design.
bitbyter
Mine will be the same but with the lamp at the top. The ballast will be in the bottom in an isolated chamber(make it bottom heavy...less tippy) then the CPUwith DVD drive mounted thru the case. Above this the mirror and object lens, then LCD/frezzi. Above this 2 sheets of super thin ultra clear glass from "frameless picture frames", the air space between the sheets will be exchanged by the fan I'm getting for the LCD panel (force fresh air between the LCD and frezzi...catch the exhaust and duct it to the twin glass sheets..then out of the case). And of course above all this is the 400 HID. My reflector is 12.5 deep by 19 wide (inchs)
I'm hoping the greatest amount of heat will rise. I havent found a need to use a condensor lens in my testing though, there is a gap of about 1.5 inchs between my frezzi and my LCD.
I was given a 10x8 foot screen case (it's brand new but dented it has no screen in it) I'm thinking of using sail cloth for a screen, nice and wide and some of it looks good for the job.
PS have you priced sonotube? The guy at the local yard gave me a price of $10.00/ft for 2foot diameter. YIKES 😱
zardoz
Mine will be the same but with the lamp at the top. The ballast will be in the bottom in an isolated chamber(make it bottom heavy...less tippy) then the CPUwith DVD drive mounted thru the case. Above this the mirror and object lens, then LCD/frezzi. Above this 2 sheets of super thin ultra clear glass from "frameless picture frames", the air space between the sheets will be exchanged by the fan I'm getting for the LCD panel (force fresh air between the LCD and frezzi...catch the exhaust and duct it to the twin glass sheets..then out of the case). And of course above all this is the 400 HID. My reflector is 12.5 deep by 19 wide (inchs)
I'm hoping the greatest amount of heat will rise. I havent found a need to use a condensor lens in my testing though, there is a gap of about 1.5 inchs between my frezzi and my LCD.
I was given a 10x8 foot screen case (it's brand new but dented it has no screen in it) I'm thinking of using sail cloth for a screen, nice and wide and some of it looks good for the job.
PS have you priced sonotube? The guy at the local yard gave me a price of $10.00/ft for 2foot diameter. YIKES 😱
zardoz
Heat Issue
I will have two fans blowing air directly underneith the fresnel that I hope will eliminate most of the heat. If they don't do the job well enough I may have to throw in a layer of heat resistant glass. At this point I know there are quite a few options to combat the heat buildup so I'm not to worried about it.
I will have two fans blowing air directly underneith the fresnel that I hope will eliminate most of the heat. If they don't do the job well enough I may have to throw in a layer of heat resistant glass. At this point I know there are quite a few options to combat the heat buildup so I'm not to worried about it.
Bitbyter
One other way to correct minor keystoning is to move the top or bottom of your projection screen forward or back if possible.
One other way to correct minor keystoning is to move the top or bottom of your projection screen forward or back if possible.
You can also tip the screen. It is not critical for the screen to be perfectly vertical. At the university I attend they have that setup in a couple of classes, the screen is up high in the air but tilted so there is no keystoning of the image on the screen... Not the best solution for massive problems but maybe for a slight problem it would work.
Projection Lens Keystone Brainstorm
A thought just occured to me. Remp mentioned that projection lenes can have keystone correction built into them. It just occured to me that the 3M 9700 OHP design may in fact have this option in use. For those of you unfamiliar with the 9700 design I will explain. In normal operation the bottom of the OHP where the mirror sits is lowered at and angle. The halogen lights are also pointing at the angled mirror on an angle. Strangley enough the mirror it self is a keystone shape. Could the projection lens used in these OHP be design to combat a natural keystone effect brought on be the space saving design of the projector? I'm hoping so because if I can get my hands on a different lens then I'm set.
A thought just occured to me. Remp mentioned that projection lenes can have keystone correction built into them. It just occured to me that the 3M 9700 OHP design may in fact have this option in use. For those of you unfamiliar with the 9700 design I will explain. In normal operation the bottom of the OHP where the mirror sits is lowered at and angle. The halogen lights are also pointing at the angled mirror on an angle. Strangley enough the mirror it self is a keystone shape. Could the projection lens used in these OHP be design to combat a natural keystone effect brought on be the space saving design of the projector? I'm hoping so because if I can get my hands on a different lens then I'm set.
Bitbyter
I dont want to give the impresion that projection lens with keystone correction are common. Far as I know they are special. We have had one instance on the forum and I personally saw keystone correction in operation at a picture theatre where I worked for a few months helping to install some new projection gear and stayed on for a month helping out. The lens were very large and expensive and adjusted with a template and small set screws in the lens body.
If your 3M 9700 had keystone correction built in it should be described in the manual or at least mentioned as a selling feature because it seems very useful.
Best of luck.
I dont want to give the impresion that projection lens with keystone correction are common. Far as I know they are special. We have had one instance on the forum and I personally saw keystone correction in operation at a picture theatre where I worked for a few months helping to install some new projection gear and stayed on for a month helping out. The lens were very large and expensive and adjusted with a template and small set screws in the lens body.
If your 3M 9700 had keystone correction built in it should be described in the manual or at least mentioned as a selling feature because it seems very useful.
Best of luck.
Oh Well
I was just speculating based on the design of the parts inside of the OHP. One can always hope for an easy solution....😀
I was just speculating based on the design of the parts inside of the OHP. One can always hope for an easy solution....😀
I think virtually every OHP has "keystone" correction. That is done simply by tilting the mirror.
Alvaius
Alvaius
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)
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 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)
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
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