Film Plane Indicator; Infrared Focusing Index - Nikon F3 Instruction Manual

Film plane indicator
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The film plane indicator
(-e-)
is engraved in white on the
top deck just behind the shutter speed dial. It indicates
the exact position of the film plane inside the camera .
Whenever it becomes necessary to measure the exact
distance between the subject and film plane, such as in
macrophotography, use the film plane indicator . The
distance between the film plane and the lens mounting
flange ® is exactly 46.5mm.
Infrared focusing index
The red dot beside the focusing index on most lenses
is the infrared focusing index. When shooting with
black-and-white infrared film, it is necessary to refocus 31
the lens to compensate for the fact that infrared light rays
focus at a point slightly in front of visible light. To use the
index, first focus on your subject through the viewfinder.
Then look at the lens and take note of the focused dis-
tance . Finally reset the focusing ring so that the desired
distance is aligned with the red dot.