lexan absorbtion spectrum
I found this light absorbtion spectrum comparing glass and lexan in a scientific paper that is online. It is a microbiology paper, but they did actually put the lexan and glass into a spectorphotometer to measure the light transmission. The glass line is on the left, lexan line is on the right.
The wavelength of violet light is from 380 to 435 nm. Blue goes from 435 to 500. Everything below 380 is ultraviolet. The graph shows the lexan transmitting almost all of the blue light, cutting out some of the violet light, and reaching total opacity by 360 nm. So it is a very good UV filter with high transmission of visible red, green, and blue that we need, and also has excellant optical clarity. (They make eyeglasses and other lenses from it.)
I found this light absorbtion spectrum comparing glass and lexan in a scientific paper that is online. It is a microbiology paper, but they did actually put the lexan and glass into a spectorphotometer to measure the light transmission. The glass line is on the left, lexan line is on the right.
The wavelength of violet light is from 380 to 435 nm. Blue goes from 435 to 500. Everything below 380 is ultraviolet. The graph shows the lexan transmitting almost all of the blue light, cutting out some of the violet light, and reaching total opacity by 360 nm. So it is a very good UV filter with high transmission of visible red, green, and blue that we need, and also has excellant optical clarity. (They make eyeglasses and other lenses from it.)
Attachments
finding fresnels
There are five Office Depots and 36 Staples stores in the NY City area. Try the nearest one to see if they have page magnifiers that are big enough. You need lenses that are large enough for your LCD, without a little higher magnification spot in the corner.
They are probably rated by Diopters, where:
Diopters = 1000/focal length
So a 3.0 Diopter has a focal length of 333 mm, etc.
There are five Office Depots and 36 Staples stores in the NY City area. Try the nearest one to see if they have page magnifiers that are big enough. You need lenses that are large enough for your LCD, without a little higher magnification spot in the corner.
They are probably rated by Diopters, where:
Diopters = 1000/focal length
So a 3.0 Diopter has a focal length of 333 mm, etc.
guy thank you very much you have been very helpful. the Lcd that iam using is 8.4'' so i guess the page magnifiers will do the trick so the highest the diopter the better or am i wrong?. Another question the Norpro reflector and a condenser where can i find these item. thanks againg for your help.
fresnel focal length
You need to find a fresnel that has a focal length a bit longer than the distance between your projector lens and your LCD. You can determine that distance experimentally, by setting up a quick and dirty optical bench:
Measure the throw distance you want to use. This is the distance between where you want your projector lens to be, and the projection screen or wall surface you will use. Then setup something to hold your lens up horizontally, that same distance from a light-painted wall or projection screen. A stack of books on a table works pretty well. Use some masking tape to hold the lens from rolling off, if necessary.
Then place a back-lit transparency with some sort of design or letters on it, behind the lens. Use one that's the same size as your LCD. Move it back and forth until you see a clear in-focus image on the wall. (of course, this works best in a dark room.) If the image size is not adequate, you can try another lens or adjust your idea about the throw distance you will use. Once you get a sharp image with the right size, measure the distance from the lens to the transparency. Then go out and find a fresnel with that focal length + about 5% more.
If you have a fresnel (or any positive lens) you can measure its focal length by taking it outside around noon with a tape measure. Move it toward the ground until you get the smallest image possible of the sun. (Don't start a fire!) Measure that distance with the tape measure. You could also do this with a lamp that is at least 30 feet away and get an answer that is close enough.
Some of the DIY projection websites sell Norpro mixing bowls or soup ladels precut to fit a big MH bulb. Or you can find your own at a discount homewares store or thrift shop. It has to be very spherical, very shiny, and big enough to get the lamp arc to the center of the half-sphere shape. Condensor lenses are a bit tougher. I think your best bet is one of the DIY projector stores like at diyprojectorcompany.com or diybuilder.com. Condensor lenses should be heat resistant glass, since they sit so close to the bulb.
But there is no reason you can't start without a condensor and reflector. They just make the image brighter. If you can get a good image up on the wall, adding these will just make it better.
You need to find a fresnel that has a focal length a bit longer than the distance between your projector lens and your LCD. You can determine that distance experimentally, by setting up a quick and dirty optical bench:
Measure the throw distance you want to use. This is the distance between where you want your projector lens to be, and the projection screen or wall surface you will use. Then setup something to hold your lens up horizontally, that same distance from a light-painted wall or projection screen. A stack of books on a table works pretty well. Use some masking tape to hold the lens from rolling off, if necessary.
Then place a back-lit transparency with some sort of design or letters on it, behind the lens. Use one that's the same size as your LCD. Move it back and forth until you see a clear in-focus image on the wall. (of course, this works best in a dark room.) If the image size is not adequate, you can try another lens or adjust your idea about the throw distance you will use. Once you get a sharp image with the right size, measure the distance from the lens to the transparency. Then go out and find a fresnel with that focal length + about 5% more.
If you have a fresnel (or any positive lens) you can measure its focal length by taking it outside around noon with a tape measure. Move it toward the ground until you get the smallest image possible of the sun. (Don't start a fire!) Measure that distance with the tape measure. You could also do this with a lamp that is at least 30 feet away and get an answer that is close enough.
Some of the DIY projection websites sell Norpro mixing bowls or soup ladels precut to fit a big MH bulb. Or you can find your own at a discount homewares store or thrift shop. It has to be very spherical, very shiny, and big enough to get the lamp arc to the center of the half-sphere shape. Condensor lenses are a bit tougher. I think your best bet is one of the DIY projector stores like at diyprojectorcompany.com or diybuilder.com. Condensor lenses should be heat resistant glass, since they sit so close to the bulb.
But there is no reason you can't start without a condensor and reflector. They just make the image brighter. If you can get a good image up on the wall, adding these will just make it better.
- Status
- Not open for further replies.