Olympus OM-2 - Manual (Page 27)

DEPTH OF FIELD SCALE PREVIEW BUTTON
The double series of numbers engraved on the
depth of field scale represents F stops: F4, F8,
and F16. Once you have focused on your subject,
all objects within the distance range indicated
on the lens distance scale between the marks for
the F stop you have selected will have acceptable
sharpness. For example, in the above picture, the
camera-to-subject distance is 3m (10ft.) and the
lens is set at F16. If you read the distance scale
at the points opposite the engraved "16" on both
sides of the reference dot, you will find that the
depth of field is from 1.9m (6ft.) to 7m (23ft.).
When you wish to see which objects fall within
the acceptable zone of sharpness (depth of field),
press the preview button on your lens. The dia-
phragm of the lens will stop down to the preset
F stop enabling you to see the depth of field in
the viewfinder.
CAUTION: If you jerk the preview button while
depressing the shutter release button halfway
down the shutter might be released.
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