To get projection image around 200cmx150cm (4:3 ratio) with OHP setup, it needs OHP to screen distance around 230cm and it will sit in the middle of my living room and I don't like it. To get the unit at the back of my living room, I need objective lenses with total focal length around 65cm and LCD panel to lenses distance become around 70cm! Problem is the fresnel panel, OHP fresnel panel can condence light at 30 to 40cm in front of the fresnel only. It's hard to find good fresnel panel with longer focal length.
From this situation the idea came up:
I will use big spherical reflector bigger enough to cover whole LCD panel, put the lamp at certain distance between 1/2R and 1R, why? if we put the lamp at 1/2R, it will produce almost parallel light beam, if the lamp at 1R, it will reflect back at the center of the reflector (most OHP use this setup). So if we adjust the lamp in between 1/2R and 1R, at certain distance, the light beam will focus at 70cm, where objective lenses sit. So... forget the fresnel panel!
To utilize some portion of wasted light beam, I put small convex lens in front of the lamp at slightly shorter than it's focal length, so it will focus the light beam at 70cm too.
What do you think? I need your comment, please...
From this situation the idea came up:
I will use big spherical reflector bigger enough to cover whole LCD panel, put the lamp at certain distance between 1/2R and 1R, why? if we put the lamp at 1/2R, it will produce almost parallel light beam, if the lamp at 1R, it will reflect back at the center of the reflector (most OHP use this setup). So if we adjust the lamp in between 1/2R and 1R, at certain distance, the light beam will focus at 70cm, where objective lenses sit. So... forget the fresnel panel!
To utilize some portion of wasted light beam, I put small convex lens in front of the lamp at slightly shorter than it's focal length, so it will focus the light beam at 70cm too.
What do you think? I need your comment, please...
Attachments
Lifter,
sorry for moving your comment at "optics help" thread here,
yes, it will work, but the problem is, when you increase (lengthen) the focal length of projection lens, you also increase LCD panel to proj. lens too. In my case the distance is about 70cm, this is way to long for OHP fresnel panel, at 70cm the light beam cannot cover the whole lens diameter and makes projected image dimmed at it's 4 corners.
see you..
sorry for moving your comment at "optics help" thread here,
yes, it will work, but the problem is, when you increase (lengthen) the focal length of projection lens, you also increase LCD panel to proj. lens too. In my case the distance is about 70cm, this is way to long for OHP fresnel panel, at 70cm the light beam cannot cover the whole lens diameter and makes projected image dimmed at it's 4 corners.
see you..
Hmmm, I was under the impression that it had no effect on the "LCD to lens" distance at all. Your not really lengthening the focal lenght of the projection lens, your running the beam through an additional lens that shrinks the image. Anyways, I really don't know since I haven't tried it, maybe ywh can jump in.
Lifter, I think it will lengthen LCD to proj. lens distance too, please take a look YWH thread below:
http://www.diyaudio.com/forums/showthread.php?threadid=11345&highlight=ywh
see you.
http://www.diyaudio.com/forums/showthread.php?threadid=11345&highlight=ywh
see you.
- Status
- Not open for further replies.