If you closely read Gary's lens tests, you will see that aperture
prefire, in addition to mirror lock up, is significant in reducing
vibration induced effects on resolution, especially with certain lenses
and/or focal lengths. It may be useful in any situation where camera and
subject don't move. I believe Gary's tests relied on sturdy tripods, and
sometimes extra lens supports, but not on "wetware" damping as
recommended by Oly: " When using a tripod, hold the camera steady with
both hands and press the shutter release with the ball of finger, not
with the cable release.", but his documentation doesn't say one way or
the other.
In any case, Paul is correct about the OM-2s and 4 series bodies and the
OM2000. He is also correct about the OM-10, OM-20/G and OM-30/F, which
fully close the diaphram and mostly raise the mirror when the self timer
is started. The OM-40/PC completely raises the mirror like the OM-4. The
OM-1 has mirror lock-up separate from the self-timer, but no aperture
pre-fire and the OM-2(n) and OM-3 and 3Ti have no such vibration
reduction functions at all. There was at least one other camera with
superior solutions back in the OM-1 & 2 days. The Nik*n F2 has a simple
mechanical mirror lock-up and aperture closing function separate from
the self timer.
Moose
Pschings@xxxxxxx wrote:
>In a message dated 8/25/2004 4:12:18 PM Eastern Daylight Time,
>jascione@xxxxxxxx writes:
>
>
>
>>How is aperture/Mirror Prefire actually performed? Is this used for
>>testing only or are there circumstances where one would perform these
>>functions? Thanks for the comments.
>>
>>
>
>On the OM-4(Ti) and OM-2S prefire is accomplished when you use the self
>timer. The mirror moves up and the lens stops down at the start of the 12
>second
>self timer cycle. The OM-1(n) has manual mirror lockup, but no aperture
>prefire.
>I think some of the double-digit OM's (OM-10, OM-20/G, OM-30/F, OM-40/PC) do
>something similar, but I think the mirror only goes partway up before exposure.
>
>I seem to recall the OM2000 did mirror/aperture prefire, and it also has a
>mechanical self timer, so the delay is somewhat adjustable - I think.
>
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