Mark Marr-Lyon wrote:
>
> >The mechanical shutter can be very accurate like the Nikon FE2, all
> >shutter has two things (or more?) to control the shutter speed, the
> >first one is the shutter traveling speed, like the OM it is 11ms and
> >Nikon FE2 is 3.3ms, it is mechanically controlled. The second one is
> >the slit width, it is electronically controlled for electrical
> >shutter. The most critical one (or the one that will affected by
> >aging) is the traveling speed, it is spring controlled.
> >
> >C.H.Ling
>
> I've been wondering about this. I'm trying to make a shutter tester,
> and am trying to figure out what the correct curtain speed is. 11ms
> is of course a time, not a speed, so the question is over what distance
> does the curtain travel in 11ms? Is it just the distance from one edge
> of the mask to the other, i.e. 36mm? That's what I thought, but in the
> repair manual for the om-1, which is the only place I've seen this, is
> a timing diagram that shows the travel time for the curtains to be 13.5ms
> from edge to edge of the mask. Ok, so maybe the distance is some standard
> distance between sensors on commercial shutter testers, and if so, what is
> it? From the numbers above, a good guess would be 30mm. Does anyone know
> if this is correct?
>
> Thanks,
> Mark Marr-Lyon
>
Yes, 11ms is a time, the time for the shutter curtain to travel from
one edge to the other. I remember it was 11-12ms for the OM-1, but
there could be other interpretation, such as the complete cycle or the
time to cover only the 36mm frame.
I expected the shutter tester will only measure one point, one point
at a time or a few point across the frame, it will not take average of
the whole frame. It is very important to check the equivalent shutter
speed at different area across the shutter, at least you have to check
the left edge, center and right edge for a horizontal travel shutter.
At highest speed, e.g. 1/1000s and 1/2000s, for a good camera the left
and right deviation could be up to 0.3 stops (or more) and still
within manufacturer's specification. But for a bad one it could be
over 1 stop, so the tester must be able to identify this fault.
C.H.Ling
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