Nikon Focusing Screens Nikon Focusing Screens Focusing screens come in a couple of basic types, usually plain groundglass matte, and a combination of matte and fresnel. The fresnel lens is added to most screens to improve brightness in the corners of the screen and provide even illumination. Other focusing aids are added to most screens, such as split-image rangefinders, or microprism focusing spots. Here is a list of the focusing screens with descriptions that are available for the Nikon F3 camera, and evaluations of their usefulness for astrophotography.
Rangefinder blacks out at high focal ratios usually encountered in telescopes.
The rest of screen is not that bright. Focusing on fresnel portion of screen more difficult than on plain groundglass screens. Not that great for astrophotography, but usable. Good with long telephoto lenses, bright. But, difficult to locate star on small 3mm fine-ground matte focusing spot which is best for focusing.