Can I use this lens with a 7" lcd? Would this be a 127mm lens? It is on an old Sears slide projector with a 500w tungsten lamp. I believe it is 3300k.

A slide projector lens is meant to "see" a slide or an object of about 2" diagonal. It would not "see" a 7" diagonal Lcd. Maybe a 2.5" Lcd at best.

I'm I missing something obvious? Wouldn't the field fresnel overcome that problem to some extent?

to some extent, but not enough extent The focal length of that lens is small and it would therefore need to be placed very close to the LCD. From this distance it would not be able to capture the entire image from the panel, regardless of the fresnel. Its field of vision simply isn't wide enough.

crappy drawing that illustrates the basic idea.. its not 100% correct



LCD & lens. yellow = light from 7" wide LCD. Blue = width of light the lens would be able to 'see'. Orange represents the distance the lens would need to be from a 7" LCD.

Where is the drawing?

maybe its blocked for you.. at work? its hosted on freeimagehosting.net, here is the URL http://img2.freeimagehosting.net/uploads/91c2c57599.gif

I can see it fine

Says I don't have permission to access uploads?

Same here.

bah I get the same thing now.. what the hell

oh well maybe its lost forever