Partial speeds on slow speed dials

I have a couple Canon bottom loading rangefinders. The older one has the older shutter design (sync speed of 1/25s) and the slow

speed dial is marked 1/25, 1/8, 1/4, 1/2, 1 sec, T.

 

When on my recent vacation, I brought this camera with and was frustrated a couple times because there is no 1/15s marked BUT I

thought I remembered something about being able to select speeds between marked speeds, although only on the slow speed dial.

 

Am I remembering this correctly? Is it possible to select in-between speeds?

 

Thanks.

<p>Yes, there's a cam on the back of the knob. But the whole mechanism probably isn't accurate enough to make the difference significant.</p>

<p>Not sure about the slow speed escapement of the Leicas. But all leaf shutters I have worked on (and I fixed quite a few) the slow speed cams did not have a continuous slope but were stepped. <br>

Even with a continuous slope you will hardly know which actual speed you will set, as there is not necesssarily a linear relationship between turning angle of the dial and speed setting. With stepped cams, setting in-between stops is not recommended - the results will just be random. <br>

BTW this is especially critical with leaf shutters where an extra part of the speed escapement is "switched on" on the transition between 1/30 (1/25) and 1/15 (1/10) sec. If you set the dial between stops in this range, the extra gear will be connected half-way and you might even get the highest shutter speed (1/250 or 1/500) as a result.</p>

<p>Intermediate (unmarked) slow speeds can be set on Leicas of the III family. However, given the latitude of all but slide films, I do not see why anyone should want to do that. Besides, such changes are easily obtained by varying lens aperture.</p>