fresnel lens from overhead projector

[Craig Wactor]

Can you use a fresnel from an overhead projector on a large format camera? I know nothing about grove pitch or focal length, why they matter and how a fresnel works. What values are good for use with a wide angle lens?

[Michael Gudzinowicz]

The focal length of the fresnel lens should be close to that of the wide angle lens.

If you don't know the focal length, project an image of the sun to a sidewalk, and measure the distance from the image to the center of the fresnel lens.

Mike

[Dan Fromm]

The ones I've seen at Edmund Scientific, now Edumund Industrial Optics but still three miles from my house, were a bit thick. The best use I've found for them was in projected flash rigs. But if you have one, trying is cheap.