Nikon F2AS Photomic Instruction Manual page 29

For fixed-aperture lenses, such as Reflex-Nikkor lenses,
simply adjust the shutter-speed selector until the center
LE D indicator comes on. For convenience, shutter
speeds can be set at intermediate settings in the 1/80 sec.
to 1/2000 sec. speed range for precise exposures. If the
meter indicates continuous overexposure, use a neutral
density filter or slower film. If continuous under-
exposure is indicated, supplementary lighting or a faster
film is necessary. This technique is also suitable for
photography using a telescope or microscope.
For bellows units, extension rings and preset lenses, set
the camera to the desired shutter speed; then, stop down
the lens manually until the center LED indicator comes
on. Preset-type lenses include PC-Nikkor lenses.
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