Rich L. writes:
<< I was surprised at your findings at 1/250 and the other instantaneous
speeds @80mm.
Yup, we were all surprised at the results, esp. given how the
photographic literature has ignored the subject of vibrations from
automatic diaphragm mechanisms. At best they have said it exists but
they never specifically test it. But the effects are so repeatable with
lightweight OM bodies, and so obvious when observing a laser point, that
most of us are now believers. Figure this zoom would show similar
improvement with mirror and diaphram prefire at its other focal lengths,
too.
<< In the real world, surely, most photographers don't usually lock up
the mirror and/or prefire the aperture at these fast speeds? >>
Landscape and architectural photographers commonly take the time to do
mirror lock-up, not to mention the obvious applications of copy work,
product photography, microscopy and astrophotography. Anytime you don't
have your hands on the camera at the time of exposure, mirror and
diaphragm prefire will probably coax a bit more performance out of your
lens.
<< I've got an OM-1n with the standard 1.8. FWIW, I've been able to
hold in the aperture stop down button on the lens with a piece of tape .
. . And is this homebrew tape method less effective, perhaps due to some
other internal movements that the prefire on the OM-4 is able to
accomplish?>>
Doing the tape bit isn't the same. The mechanical couplings within the
body are still in movement immediately before exposure and their
residual vibrations are still present during exposure, due to the short
time lag between pressing the shutter release and actual exposure.
<< Do you think this is an effective method? >>
Don't ask the preacher. Ask the choir and read the results, esp. the
extensive comparisons for the 200mm f/4 - all using the same lens.
Previous dialog about this technique can be found in the OM List
archives, so you're really revisting an old issue - but we're happy to
fill you in.
Incidentally, most Nikon manual focus cameras give mirror and diaphragm
prefire with self-timer use, as do the earliest Minolta, Ricoh and Canon
SLRs. Another example of feature shedding, perhaps? It isn't a problem
that has gone away.
<< Or is there still some differences in the shutter curtains operation
between the OM-1s and the current OM-4ti? >>
Sure, but in what respect? Even the most modern OM shutters will
vibrate the camera/lens combo on a tripod. I'm going to put a
disclaimer before the >500mm lenses saying that it's impossible to
control shutter vibration at speeds where you can't touch the camera at
time of exposure. That horizontal vibration is very detectable, even
with two tripods with their spike feet frozen into an ice rink. Vertical
resolution bars smear and horizontal ones are distinct. That says you
are getting horizontal vibration at time of exposure.
<< Also, what is a Bogen Telephoto Lens Support? >>
a sliding cradle with a tripod socket in the middle, a velcro strap and
V-shaped lens cradle on one end and a platform for the body on the other
end. It prevents the kind of flex you get at the tripod socket from
hanging a long, tripod collar-less lens off the from of a OM body. It
is especially useful in tripod work with the 180mm, 200mm, 65-200mm, and
100-200mm Zuikos. A pain to pack, though.
Gary Reese
Las Vegas, NV
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