[Leica] Re: DR summicron and M4-P

[pieter@world.std.com (Pieter Bras)]

Peter Niessen <niessen@ifh.de> wrote:
>
>I understand that when changing a DR Summicron lens the focus _has_ to
>be set to infinity. I do not know why, though.

Take a look at the rear of the focusing mount. There is a cam that
engages the camera's rangefinder mechanism.  Usually this is just a
single surface, but in the case of the DR Summicron, there are two
sections, separated by a step.  The protruding section is for the
near range.  However, when the lens is in the normal range, this near-
range cam protrudes beyond where the rangefinder's follower (the little
wheel) can move.  If you try to mount the lens when it's focused at the
short end of its normal range, there is a good possiblity that the
near-range cam will engage the follower, and bend it out of position.
This will result in a misaligned or damaged rangefinder.

I learned this the hard way, by mounting my DR on an M4-P when it was
focused to about one meter.

Once the lens is moved into the near range, the near cam becomes safe.
Thus, you can also mount and dismount the lens in its near range, at the
position where the DR finder can be mounted.  In any case, the finder
must be removed to mount/dismount the lens.

The DR Summicron was designed for the M3.  I have the instruction book
for the M3 and the "how-to-use" leaflet for the DR Summicron and
interestingly enough, there is no mention of any need to focus the lens
to infinity before mounting it on the M3.  Perhaps the M3's rangefinder
mechanism does not suffer from this restriction.

- -- 
Pieter Bras