When you take a photograph using a single lens reflex (SLR) camera there
are three things that must happen before the exposure can be made.
(1) The viewing mirror (which is located between the lens and the film)
must be flipped up out of the way so that the light can get to the film.
(2) The diaphragm of the lens must be closed down to the shooting
aperture. The lens diaphragm is normally wide open to allow the maximum
amount of light for ease of focusing. However at the time of exposure
it must be closed down to restrict the amount of light in order to
control the exposure (in conjunction with the shutter speed which also
controls exposure).
(3) The shutter must be opened.
All three of these actions require fast, mechanical motions which will
induce vibrations in the camera as mechanical pieces of the mechanism
are suddenly accelerated and then abruptly stopped.
These vibrations, however, are only important when using moderately slow
shutter speeds (say, 1/2 second to 1/60 second) and high magnification
as in very long telephoto lenses or macro photography (extreme
closeup). With very slow shutter speeds the period of time that the
camera is vibrating is short with respect to the shutter speed and the
light admitted to the camera during the vibration period doesn't
contribute much to the total exposure. If using faster shutter speeds
the exposure is over quickly and the vibration of the camera is
"frozen".
In the OM-1, mirror lock-up helps to eliminate one of these sources of
vibration but not all three. The OM-2 has a specially designed shock
absorber on the mirror mechanism designed to minimize but not eliminate
the mirror induced vibration. When using either camera for critical,
high magnification photography the camera must first be mounted on a
tripod. Secondly, the camera should still be cradled in the hands or
draped with a bean bag or other means used to absorb the vibrations of
mirror, diaphragm and shutter.
In the OM-2sp, OM-4 and OM-2000 the self-timer mechanism "pre-fires" the
mirror and diaphragm mechanisms 2 seconds before the shutter is opened.
This give the camera vibrations time to settle down before the exposure
is made. This still leaves a minor source of vibration from the the
shutter itself.
All of this is terribly UNimportant for most everyday photography and I
would not let it be the determining factor in choosing an OM-1 or OM-2.
Base your decision on other things and don't let the battery situation
get in the way of an OM-1 since there are many solutions there.
Chuck Norcutt
Woburn, Massachusetts, USA
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