Archived posting to the Leica Users Group, 1998/07/08

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Subject: Re: [Leica] same exposures???
From: Five Senses Productions <>
Date: Wed, 08 Jul 1998 21:50:08 -0700

So if I notice this phenomenon on every lens, it must be the shutter of the
M6, and if this phenomenon only occurs with the 35/2 ASPH, then the lens
aperture is nonlinear?
And if it IS the shutter, this can be fixed by tightening a screw somewhere?
And if it IS the lens, what can be done?


>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?