Problem solved. The panel is now about 3/4" higher than it was before, and the rings have dissapeared completely. I never thought a screen door would look so beautiful.
New problem. There was no noticable loss in brightness, but now I have some of the sides hacked off because of the "pyramid" beam. The illuminated area of my 15" screen has now shrunk.
New problem. There was no noticable loss in brightness, but now I have some of the sides hacked off because of the "pyramid" beam. The illuminated area of my 15" screen has now shrunk.
Lifter,
Sorry that the Roscolene sources didnt pan out. Im sure another google search would have found someone selling the stuff.
Good news about repositioning the panel. So to solve the new issue of the screen falling outside the light path, I was thinking that moving the bulb farther away from the fresnel would be the solution. Yup, easier said that done. Think about it this way, a fernel spotlight is little more than a bulb and a CHEAP fresnel lens. The beam width is set by sliding the bulb back and forth behind the lens. The further the bulb from the lens, the narrower the beam.
So then the question becomes, if you cut the bottom out of your projector and build an extension that allows you to adjust the beam width, will the optimum beam width cause the return of the moiré issues? I don’t think so. Going back to the analogy of the fernel, the focus is actually controlled be the distance of the bulb to a reflector that travels with its base. The bulbs motion only controls the beam width. Having your panel in on a separate focal plane from the lens should keep the lines from re-appearing. Of course I’m SO CERTAIN that this will work, that I will also include the disclaimer of suggesting that any modes you try are highly reversible. Just in case. Optimally, a modification would allow for the bulb to be slid about until the optimum location can be found.
Clear as mud, huh?
- Dave
Sorry that the Roscolene sources didnt pan out. Im sure another google search would have found someone selling the stuff.
Good news about repositioning the panel. So to solve the new issue of the screen falling outside the light path, I was thinking that moving the bulb farther away from the fresnel would be the solution. Yup, easier said that done. Think about it this way, a fernel spotlight is little more than a bulb and a CHEAP fresnel lens. The beam width is set by sliding the bulb back and forth behind the lens. The further the bulb from the lens, the narrower the beam.
So then the question becomes, if you cut the bottom out of your projector and build an extension that allows you to adjust the beam width, will the optimum beam width cause the return of the moiré issues? I don’t think so. Going back to the analogy of the fernel, the focus is actually controlled be the distance of the bulb to a reflector that travels with its base. The bulbs motion only controls the beam width. Having your panel in on a separate focal plane from the lens should keep the lines from re-appearing. Of course I’m SO CERTAIN that this will work, that I will also include the disclaimer of suggesting that any modes you try are highly reversible. Just in case. Optimally, a modification would allow for the bulb to be slid about until the optimum location can be found.
Clear as mud, huh?
- Dave
Clear as mud is right. I'm a little confused. Cut a hole in the bottom of the OHP (not going to happen, I'd buy a new lamp/ballast and build an enclosure before doing that)? How is lowering the bulb different then just raising the fresnel?
I'm getting a 14" focal lenth fresnel in the mail. That should help.
I'm getting a 14" focal lenth fresnel in the mail. That should help.
No, I didn’t claim it was good advise.
I guess what I was thinking was that this would allow for some level of adjustability.
I think it also allowed me to show off my inherent distaste of overhead projectors: Too many hours staring at concentric rings while someone droned on and on in a stuffy lecture hall.
The new lens should help a lot.
I guess what I was thinking was that this would allow for some level of adjustability.
I think it also allowed me to show off my inherent distaste of overhead projectors: Too many hours staring at concentric rings while someone droned on and on in a stuffy lecture hall.
The new lens should help a lot.
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