ScottGee1 wrote:
>The 50/1.4 lens I got with my 4T seemed to have a somewhat sluggish
>iris. Thinking it might be wise to 'work' it, I stopped it down a
>pressed the DOF button quickly numerous times. After approximately a
>half dozen actuations, the shutter fired. Assuming I accidentally hit
>the shutter release, I advanced the film and did it again and
>duplicated the effect.
>
>The other lens does NOT do this.
>
>Is this a feature?
>
>
Sure, why not? :-) Actually, it is not an uncommon problem and has
discussed before. Clint said:
"A lot of people don't realize that when you "fire the shutter" on an SLR,
you're not really releasing the shutter -- you're releasing the mirror, and
the mirror trips the shutter once it moves up out of the way. And on OM's at
least, the same mechanism that lifts the mirror also stops down the lens'
aperture. When you "work" the DOF button, it may be jiggling the aperture
stop-down arm enough to make it "fire", releasing the mirror then firing the
shutter."
It is certainly repairable, as he goes on to discuss in the 2/13/2003 post "Re:
[OM] OM-3 problem -- triggering of shutter by pressing DOF preview"
However, it sounds like you had to work pretty hard to make it happen. If it
never happens in normal use, why don't you "exercise" your diaphram with the
lens off the body and not worry about it. Then it's easier too, as you can just
work the diaphram lever/tab directly.
Using the lever directly brings us back to the original problem. There are two
basic causes of slow diaphram return. One is oil in the diaphram mechanism,
which requires relatively serious disassembly to clean. The other is oil in the
DOF button mechanism. You can tell which you have by moving the tab/lever on
the back of the mount and litting the spring snap it back. If the diaphram
snaps open too, you have a sticky DOF mechanism, otherwise, it's in the
diaphram itself.
A sticky DOF button mechanism is easy to clean by removing the 3 cross point
screws that hold the mount on the lens, carefully pulling it off, cleaning the
big "C" shaped lever that the DOF button pushes and reassembling. Here's a pic
of the open back of an 85/2, showing the DOF mehcanism. The 50/1.4 is
practically identical <http://www.moosemystic.net/Gallery/85_mount.jpg>.
>BTW, did/do any of the third party lenses made for OM mount have DOF
>buttons? I know the couple Tamrons I own do not.
>
>
I have quite a few 3rd party lenses and they all have DOF buttons or
levers. The original Tamron Adaptall mounts for OM didn't have any DOF
function. The FAR more common Adaptall2 mounts have a flat, serrated tab
on the adaptall that slides radially to close the diaphram. Slide, not
push. If you have the old style, just get an adaptall 2 and exchange mounts.
Moose
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