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This film has been interferometrically tested to have a 94-96% relative density.
Detailed installation instructions
Important note: 3.8 optical density photo film MUST NOT BE USED FOR VISUAL OBSERVING. Also, for astrophotography, is should only be used for taking images of the Sun at high magnifications - and in conjunction with a suitable projection eyepiece. It is only necessary for making short exposure times possible despite very high magnifications with extremely long telescope focal lengths. 3.8 photo film is also not intended to be used directly in front of a camera lens. The resulting image brightness would be too high.
When looking directly through a telescope with front-mounted 3.8 OD photo film, for checking the solar image for example, a UV/IR blocking filter plus a factor 1.8ND vacuum deposited/neutral density filter MUST be placed in the light path - or at least held in front of the eye by hand.
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Important note: solar film for photography, with an optical density of 3.8, must not be used for visual observing. And even for photography, this solar film is only to be used for exposures of the sun at high magnifications and in conjunction with a suitable projection eyepiece. However, this is only necessary for achieving short exposure times with very high magnification when using extremely long focal length telescopes. 3.8 photographic solar film is also not suitable for mounting directly in front of a camera lens. The resulting image brightness would be much too high.
For direct observing, when checking the image through a telescope with front-mounted 3.8 OD photographic solar film, a UV IR blocking filter (# 2459207A, Section 43B) together with a 1.8 factor attenuating/neutral density filter (# 2458345, Section 39) are always additionally required - either mounted in the light path, or at least held up in front of the eye.
(Marcus Schenk)
