Projector Experts?

[ByRiker'sBeard]

I was wondering if anyone knows a lot about projectors? I was wondering if there is a special external lens that can take an image not projected flatly on a surface and reverse any distortions? I know protractors often can do that to a degree digitally, but pixels start to look stretched. I want to see if I can make it look cleaner.

 

[petrochemist143 168]

I'm sure it would be possible to create additional optic to remove such distortions, but they would have to be designed specifically for each use case so it's very unlikely any have been made. Even if they have they probably wouldn't even be an improvement for your particular use case.

 

[AlanKlein108 24]

I was wondering if anyone knows a lot about projectors? I was wondering if there is a special external lens that can take an image not projected flatly on a surface and reverse any distortions? I know protractors often can do that to a degree digitally, but pixels start to look stretched. I want to see if I can make it look cleaner.

I'm assuming your problem is a keystone effect because the camera is aimed slightly up at the screen? Is the picture wider at the top than the bottom? If this is the case, can you raise the projector on a stand on the table so it projects square to the screen?

 

[petrochemist143 168]

I'm assuming your problem is a keystone effect because the camera is aimed slightly up at the screen? Is the picture wider at the top than the bottom? If this is the case, can you raise the projector on a stand on the table so it projects square to the screen?

I hadn't thought of that possibility! Among my collection of projector lenses is one designed to shift sideways relative to the center of the image - this shift is specifically used to counteract this keystoning, in just the same way the shift lenses are used to control perspective.
Here's my 40mm perspective control projector lens (adapted via extension tubes & a helicoid for use on a camera)
40mm perspective control projector lens mounted by Mike Kanssen, on Flickr

Perspective control projector lenses are not common but at least they are available

 

[ByRiker'sBeard]

I'm assuming your problem is a keystone effect because the camera is aimed slightly up at the screen? Is the picture wider at the top than the bottom? If this is the case, can you raise the projector on a stand on the table so it projects square to the screen?

I have a projector that I want to connect to a computer and I want to project on the ceiling. The projector will be in the corner of the room. I do have a first surface mirror, but that may only be useful if I am bouncing light at a 45 degree angle horizontal then up, but the image may be too large by the time it gets to the middle of the room and won't stay within the area of the mirror. I would need to throw the image further, but it will become more trapezoidal. I wasn't sure if there is a lens that makes it as though the light is hitting the ceiling at 90 degrees so it won't stretch, or rather is warped the opposite way first so it cancels it out.

 

[AlanKlein108 24]

I'm assuming your problem is a keystone effect because the camera (projetor)is aimed slightly up at the screen? Is the picture wider at the top than the bottom? If this is the case, can you raise the projector on a stand on the table so it projects square to the screen?

I hadn't thought of that possibility! Among my collection of projector lenses is one designed to shift sideways relative to the center of the image - this shift is specifically used to counteract this keystoning, in just the same way the shift lenses are used to control perspective.
Here's my 40mm perspective control projector lens (adapted via extension tubes & a helicoid for use on a camera)

40mm perspective control projector lens mounted by Mike Kanssen, on Flickr

Perspective control projector lenses are not common but at least they are available

I meant to say projector, not camera, in my earlier post copied here and corrected. Was the aiming of the projector on a tilt the problem?

 

[petrochemist143 168]

I meant to say projector, not camera, in my earlier post copied here and corrected. Was the aiming of the projector on a tilt the problem?

I hadn't noticed your typo, the lens I was talking about was designed for projectors I've just used it for something else

Having a highly sloping screen (relative to the projector axis) will give issues with focus, but I think tilt shift operations as used in large format photography should be able to deal with that.

FWIW the rules of optics used in lenses don't care if the optical system is taking an image from a physical subject or projecting the image from a slide. The rays follow the same path if going backwards...