WayneS wrote:
> At 11:50 PM 12/22/2008, Moose wrote:
>
>> John Hermanson wrote:
>>
>>> Yes, on the 3 and 3Ti they coulda shoulda used a self timer mechanism right
>>> out of an OM-1.
>>>
>>>
>> And yet ... those are pretty useless. It seems to me that Gary's lens
>> tests showed pretty conclusively that the mirror lock-up of the OM-1 was
>> singularly ineffective at controlling vibration.
>>
>
> The amount of force required to make sure every possible lens aperture could
> be operated in time, is what causes a lot of vibration.
>
I've occasionally wondered about Maitani's reasons for choosing the
mechanical design he did. The Nikon auto diaphragm design already
existed and Maitani chose to go the opposite way. Simple contrariness?
Sounds like me. :-)
The OM body has to operate the diaphragm lever on the lens against the
mechanical friction and spring tension of the lens to stop it down for
exposure.
The Nikon design has the lens diaphragm held open against its own,
internal spring tension for full aperture viewing/focusing. The stop
down mechanism need only allow the lens to stop itself down. Rather like
automation of a preset lens. I assume that means the spring tension will
be lighter on smaller lenses, which seems to be the case with 200/4 and
50/1.4.
So there would be less radial momentum to cause vibration with smaller
lenses. Perhaps more importantly, the diaphragm actuation mechanism need
not bang to a stop at the end of its travel. I have no idea how it is
designed, but cam operation that doesn't allow the lens tab to hit the
end of its slot would keep the spring from accelerating the mechanism
and give almost no jolt at the end of travel.
All a moot point all these years later, but certainly the Achilles heel
of a generally brilliant design.
> Hence aperture pre-fire solves a lot of vibration issues with the OM's. And
> not something the OM-1 can do. The OM-4t with self-timer works.
>
Yup, and as I said in my post, also officially, the OM-Sp, original
OM-4, OM-40(PC) and OM2000. Unofficially, I seem to recall the the OM-20
also closes the aperture and puts the mirror about 2/3 of the way up
when the self timer starts.
Moose
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