Focusing for Astrophotography - Film Considerations Focusing for Astrophotography Film Focusing tolerances will depend in part on the resolution that the film is capable of recording. High resolution film, such as Kodak's Technical Pan film, combined with a high resolution optical system and good seeing and tracking require much more critical focusing. Film Construction Film is composed of several layers. The emulsion, containing the light sensitive compounds, is suspended in a gelatin that is coated on top of a base layer that is made of acetate or polyester.
Color film has three or more emulsion layers sensitive to different colors.
Film may also include an anti-halation layer and for color films, a masking layer. Films come in different thicknesses. Tech Pan is a very thin film. Fuji's Velvia is a very thick film. As discussed previously, the thickness of the film must be taken into account during focusing.