Re: [Leica] Re: Using the Russar 20mm on the Bessa R or L and other oddball combinations

["Dante A. Stella" <dante@umich.edu>]

Good point.

In fitting the Industar (Elmar), Summar, Collapsible Summicron, 35 Jupiter
and the like to the Hexar, I have not had any problems (it looks like the
lens cavity is specifically designed to handle big rear elements and
collapsing barrels - the Jupiter exactly fits the cylindrical form of the
chamber; and the Summicron, Summar and Industar come to rest about 1mm
from the shutter).  Somebody clearly thought of this problem.  Or had his
favorite LTM lenses in mind when designing the body.

Cummer Family wrote:

> Dear LUGGERS,
> >From the archives May 31, 2000 Doug Richardson tells all:
> Howard.
> >If you use a "Voigtlander" Bessa or Konica Hexar, and fit only the
> >company’s own lenses or modern Leica lenses, you may cheerfully ignore
> >this posting. However, if you like experimenting with older Leitz and
> >non-Leitz lenses on your camera, read on.
> >
> >It’s tempting to assume that any lens which will fit a Leica will also
> >fit the Japanese-built Bessa and Hexar cameras, but this it not always
> >the case.
> >
> >A few days ago Howard Cummer was passing through London, and wanted to
> >try some of my older Leitz and non-Leitz screw-mount lenses on his
> >rangefinder Bessa.
> >
> >Howard was interested in trying my KMZ 20mm f5.6 Russar, but found
> >that the protruding rear section if this lens fouled on the internal
> >structure of the Bessa, preventing it from being screwed home.
> >
> >The was a simple problem whose after-effects can be removed by the
> >application of a little matt black paint to the metalwork which had
> >made inadvertent contact, but a more complex problem emerged when
> >Howard tried my 5.8cm f1.5 Leica-Sonnar. (This is a lens which the
> >average Bessa or Hexar user is very unlikely to meet, but it’s
> >possible that other oddball lenses might have the same problem.)
> >
> >The lens would not unscrew from his camera, but would turn only a few
> >degrees anticlockwise before sticking!
> >
> >Reasoning that the problem might be due to the rangefinder cam, I
> >focussed the lens to its shortest distance, and was then able to
> >unscrew it. Looking at the rear of the lens, it soon become clear what
> >the problem was.
> >
> >While a traditional Leica lens has a cam whose rear face lies parallel
> >to the rear if the mount, and which moves in and out to couple to the
> >rangefinder, the cam on the Leica-Sonnar and the 40mm Summicron-C for
> >the CL Summicron-C (and presumably the 90mm C lens) has a sloped
> >rangefinder cam which  achieves its effect by a combination of moving
> >in and out and by turning to bring a higher or lower section of the
> >cam against the rangefinder sensing roller.
> >
> >When a lens set to infinity, the cam is as far rearward (i.e. deep
> >into the camera body) as it will go, and the position of the
> >rangefinder roller is thus as deep into the body as it needs to go. As
> >the lens is refocussed to shorter distances, the cam retracts into the
> >lens, and the rangefinder roller moves forward
> >
> >On the 40mm Summicron-C, turning the lens mount from infinity to
> >closer range not only retracts the cam into the body of the lens, but
> >also brings a lower point of the cam into contact with the rangefinder
> >roller. The slope of the cam thus increases the effect of the cam
> >retraction. On the 5.8cm Leica-Sonnar the slope works in opposition to
> >the cam retraction. Turning the lens mount from infinity to closer
> >range retracts the cam into the body of the lens, but brings a higher
> >point of the cam into contact with the rangefinder roller.
> >
> >The problem with the latter scheme is that when the lens is set to
> >infinity (and the rangefinder roller is as far back into the camera
> >body as it needs to go), other parts of the cam penetrate even deeper
> >into the body. So if a lens of this type is to be screwed into and out
> >of the camera body while set to infinity, the rangefinder roller must
> >be able to move a further 2mm into the body in order to ride up and
> >over the highest point of the cam.
> >
> >On a screw-mount or M Leica, the rangefinder mechanism can cope with
> >this extra movement, but it seems that the Bessa rangefinder will not.
> >
> >Like many screw-mount enthusiasts, Howard sets a lens to its shortest
> >distance before fitting it to the camera. Before trying to remove the
> >lens, he’d refocussed it to infinity, and the rangefinder roller had
> >been unable to cope with the highest point of the cam, so prevented
> >the lens being turned further.
> >
> >At this point Konica Hexar users are probably saying to themselves,
> >"My camera has a bayonet mount, so I’d have no problem, even if it
> >turns out that the Hexar rangefinder roller cannot move deeper than
> >the infinity position."
> >
> >Care may still be needed however. All Leica lenses (and most
> >Leica-compatible lenses from other manufacturers) turn anticlockwise
> >as seen from the front to change the focus from infinity to closer
> >distances. However, the Leica-Sonnar (and perhaps some other non-Leitz
> >lenses) turns in the opposite direction!
> >
> >On any variable-height (sloped) cam lens there is obviously at some
> >point around the circumference of the cam when the low part meets the
> >high part. With the Leica-Sonnar fitted and focussed to infinity, the
> >rangefinder roller is sitting at the lowest point on the cam, and just
> >to its right (as seen from the front of the camera) the cam slopes
> >upwards at an angle of around 30 - 40 degrees to reach its highest
> >part. The act of mounting and unmounting the lens will thus bring this
> >high point against the roller, requiring the latter to move the extra
> >2mm deeper into the camera body, which it may or may not be able to
> >do.
> >
> >So if you want to try another manufacturer’s lens on your Bessa or
> >Hexar, I’d recommend that you make sure that the lens uses a
> >Leitz-style parallel cam. If it does not, check where the step in the
> >cam lies when the lens is focussed at infinity and minimum distance,
> >and how that step will move as the lens is mounted and removed. The
> >safest measure will probably be to mount and unmount the lens with its
> >focusing set to minimum distance to draw the cam as far as possible
> >into the body of the lens. (The most important exception to that rule
> >is the dual-range Summicron, which has two cams at different heights,
> >and which should be fitted and removed with its focusing mount set to
> >infinity.)
> >
> >Regards,
> >
> >Doug Richardson
> *Thanks Doug.
> * Howard