Try locking the mirror up, then (if memory serves me)
advance the lever (with no film in) and operate the
self timer with the speed set to "B", as soon as the
shutter opens and you can see the pressure plate
through the lens flange, operate the lever to halt the
self timer from winding on (thereby locking the
shutter open), use a vernier caliper to measure the
distance from the flange to the film pressure plate.
If you want to be super accurate, measure the
thickness of a piece of film and add that to your
final figure.
To close the shutter afterwards, make sure you have
nothing inside the camera (vernier etc) operate and
lever for the self timer (and the shutter should close
again at the end) and flip down your mirror.
Chris
--- Bill and Pam <clar132@xxxxxxxxxxxxx> wrote: > Hey
all,
>
> I have been using my OM1(n) for
> astrophotography (as well as regular photography)
> for some time now. Any other astronomers out there?
> I now want to get a bit more picky with my exposure
> times. To do this, I need to know the distance from
> the film plane to where the lens rotates on (I
> forget what this part is called; lens flange?
> camera flange?). Does anyone out there have such a
> measurement? Maybe our friend John H.? I would try
> to do it myself, but I do not want to damage the
> shutter or anything (no tools to measure here). Any
> experts out there?
>
> Please respond to the list as I will be offline.
>
> Thanks in advance!!!
>
> -Bill Clark
>
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