Re: [Leica] same exposures???

[Mark Walberg <Walberg@simmons.swmed.edu>]

Francesco,  One possibility is that the tension on the shutter curtains is
off.  If so, this would cause the result you've got.  One way to tell
whether this is true is to take flash pictures at all of the speeds higher
than the synch speed.  The width of the slit exposed by the flash can then
be measured.  The width should be halved for every doubling of the shutter
speed.  If the width decreases by less than half for each shutter speed
doubling, then the second curtain tension needs to be increased until it is
halved with every speed doubling.     Another quicker way to do this is to
try to measure it by eye instead of on film.  Open the back of your camera,
put a light in front of it, and fire the shutter at the different speeds.
You can estimate the slit width by eye this way.  You can even hold a ruler
up at the back to measure it.
  I have not adjusted the curtain tension on a Leica, but usually it is
done with a screwdriver on a screw under the bottom plate.  I couldn't tell
you which screw is the right one on a Leica.  Someone here might know.
   Of course, it is conceiveable that the aperture on your lens is
nonlinear.  If that is the problem, it will show up only with that lens.
If it is the shutter, then it will show up with all the lenses.
- -Mark Walberg

>I recently ran an informal test on some film I was trying for the first time
>(Sensia II).  I rated the film at different aperture/shutter combos, always
>at the same exposure.  For example, if the exposure from my incident
>meter was 1/250 @ f/8, I would also try 1/500 @ f/5.6, 1/1000 @ f/4,
>and 1/125 @ f/11.  This was on my M6, by the way.
>
>I found that as the apertures got smaller (towards f/16), the slides were
>slightly darker, and as the aperture enlarged the slides were slightly
>lighter.  I have noticed this before, but didn't think much of it since the
>decrease or increase of light is only 1/4-1/3 stop per f-stop.
>Shouldn't a slide exposed at 1/250 @ f/8 look EXACTLY like a slide
>exposed at 1/60 @ f/16 or 1/1000 @ f/4 ??  I thought the only thing
>that would change would be motion-freezing ability (the shutter speed)
>and DOF (the aperture).  Does this signify a probem with my M6, or is
>this a phenomenon well-known by everyone but me?
>
>Francesco