Ok heres the deal, i built a projecter using a lcd panel and built sort of a OHP setup. Anyways up till now ive been using the fresnels from the 150" big screen kit (in front of and behind th lcd) and a 320mm triplet lens but decided it was time to trade up so i ordered the basic fresnel lenses from lumenlab and when i put one in back of and one in front of the lcd the best picture i could get was only a circle of the middle of the screen with the rest to dark to see, i tried switching the lenses around and found out that one is different than the other when placed behind the lcd, but that didnt help. At last i put one of my new fresnels behind the lcd and one of my old crappy ones in front and got and image that is pretty much identical to the one that i used to have with the two crappy fresnels.
can anyone point out the right way to set up the lenses from lumenlab so i can get a good full picture?
can anyone point out the right way to set up the lenses from lumenlab so i can get a good full picture?
You should have a 220mm and 317mm fresnel from lumenlab. The 220mm one goes behind the lcd and your light sorce must be 220mm from center of the bulb arc to the fresnel. The 317mm goes infront and you focus your triplet on the lcd at around 330mm or so (you'll have to play with it to get it focused) depends on how far from the wall image size ect.. Both groove face towards the LCD.
Clinton
Clinton
fresnels
Hi All:
Thanks for the clear instructions Clinton, they help me too. One thing confuses me, though. I'm buiding my first projector, using a Proxima Ovation a822c and a 400 watt metal halide M59 bulb (and LOTS of forced-air cooling). The image is large enough for my needs already, I don't need to expand it (I'm using a HUGE lens from an old Vulyte III Opaque Projector, it's awesome. Probably about six pounds of glass, it's about five inches across, collects light like you wouldn't believe ...). I just want the fresnel to diffuse the light evenly across the panel (the bulb puts out a whopping 38,000 lumens at 4,000 kelvin, have to use IR glass and a UV filter to cut down the nasty part of the light spectrum...).
My question is this - all overhead projectors have BOTH fresnels underneath the LCD panel, and they work fine. What's the advantage of using a split fresnel and putting one fresnel "under" the LCD and one "over" it? Can't I take an unsplit fresnel and just mount the whole thing an inch or so under the LCD (ie. between the light source and panel) to spread the light ...?
Thanks,
IJ
Hi All:
Thanks for the clear instructions Clinton, they help me too. One thing confuses me, though. I'm buiding my first projector, using a Proxima Ovation a822c and a 400 watt metal halide M59 bulb (and LOTS of forced-air cooling). The image is large enough for my needs already, I don't need to expand it (I'm using a HUGE lens from an old Vulyte III Opaque Projector, it's awesome. Probably about six pounds of glass, it's about five inches across, collects light like you wouldn't believe ...). I just want the fresnel to diffuse the light evenly across the panel (the bulb puts out a whopping 38,000 lumens at 4,000 kelvin, have to use IR glass and a UV filter to cut down the nasty part of the light spectrum...).
My question is this - all overhead projectors have BOTH fresnels underneath the LCD panel, and they work fine. What's the advantage of using a split fresnel and putting one fresnel "under" the LCD and one "over" it? Can't I take an unsplit fresnel and just mount the whole thing an inch or so under the LCD (ie. between the light source and panel) to spread the light ...?
Thanks,
IJ
If you split it you get better edge to edge brightness, better contrast control as well as the opion to correct keystone. Also i found with playing with my 3M9700 the fresnel is "just" big enough to fit my LCD. Laying it on top of the unsplit fresnel it missed 1/2" on either side of the image cause the light is already throught the collector fresnel. I split them and now i get parallel light passing through the LCD which lights the whole screen. Hope that helps.
Clinton
Clinton
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