Can I use any fresnel?

[Marcus Carlsson]

Hi,

I wonder if I can attach any type of plastic fresnel on my GG? I have made the GG myself, so size doesn't matter, but I wonder if there are anything I have to look for when adding a fresnel (if for instance the fresnel only work for a special lens etc)

/ Marcus

[Donald Qualls]

If you put the Fresnel between the ground glass and your eye, you can use pretty much any Fresnel you like. If it's between the ground glass and lens, it'll be most effective if the focal length is matched to that of the lens, and you'll need to offset the Fresnel-ground glass pair toward the lens from the film plane by approximately 2/3 the thickness of the Fresnel to maintain focus registration.

[Marcus Carlsson]

ok, that sounds smart.
Thanks

[Struan Gray]

If you are looking at cheapie reading fresnels a 3x or 2x model will do fine for all but the most exotic wide angles. You won't need it for long lenses. I use the midi sheet magnifier from here:

http://www.magnifyingglasses.co.uk/acatalog/Online_Catalogue_Page___Sheet_Magnifiers_8.html

for 150 mm and 90 mm lenses on 4x5 and it evens out the illumination nicely for composing. For focussing it muddies the image through the loupe, and the grooves can be distracting, so I remove it - it's only held in by hand or by a blob of blu-tak (häftmassa).