Re: [Leica] Konica facts

[Stephen Gandy <Stephen@CameraQuest.com>]

Very interesting,  but a few questions.

#1  how many Hexar's were examined, and what were the serial numbers ?
Konica may have corrected the problem in later bodies.

#2  this problem has been discussed on the LUG.  On Feb 4, 2001  Akhil Lal
made a LUG post entitled "Re: Min. focus accuracy of Leica lenses and the
Hexar RF"  which according to the message header, was also emailed directly
to you separately.  In that email Bob Shell is quoted as saying the Hexar
back focus is not identical to the Leica M, and a Rollei list thread
questioning the back focus is also referred to.

#3  According to a friend of mine who works as a consultant with Konica, the
problem is not so much an intentionally chosen different back focus, but how
the in some cameras the COMBINATION of individual tolerances of different
parts can COMBINE to unacceptable levels, ie a combination of parts all with
the larger tolerances will combine to make too large a total tolerance.
This is another way of describing the mechanical tolerance issue you make
note of.

He told me that not only is Konica Japan is aware of the problem, but they
are taking in cameras to be adjusted to Leica M tolerances and adjusting
them for free.  I emailed Konica USA on this several weeks ago, and got the
same response from them that I got in February after Akhil's post --
nothing.

#4  So, it would seem to have a good idea to have individual Konica Hexar
cameras tested for back focus to M specs, until at least a large enough
sample confirms how common this problem is.  It may exist with some cameras,
but not others.

Stephen Gandy


Erwin Puts wrote:

> There has been much discussion about the compatibility of Leica lenses
> with the Hexar RF body. Most people, including all of the magazine
> writers have assumed that the study of the bayonet mount (that is does
> the Leica lens fit onto the Hexar bayonet) is sufficient to declare that
> lenses and bodies can be safely intermixed. Problems have been
> encountered and have been discussed as tolerance issues. As far as I
> know, no one has extended the analysis to the most crucial part: the
> back focus or the distance from bayonet flange to film plane. After
> measuring it  and checking with the Konica people a most surprising fact
> emerges.
> The back focus of the Hexar RF is 28.00mm with a tolerance bandwidth of
> 0.06mm!
> The Leica data are: 27.80mm with a max tolerance of 0.02mm.
> The first observation is this. Leica tolerances are 3 times as narrow as
> the Konica ones (0.02 versus 0.06). Wonder why the Leica is expensive?
> This small difference in tolerance is a hefty task in production
> engineering.
> Most importantly however is the conclusion that Leica lenses cannot be
> used with any degree of confidence or performance on the Hexar. The back
> focus difference of 0.2mm and that is much too large for even  a modest
> demand on optical performance. It simply means that the leica lens
> focusses 0.2 mm short of the film plane. A distance that is wide enough
> to kill any idea that we are talking about precision optics or
> engineering.
> Nor can we use Hexar lenses on leica bodies, now the Hexar lenses will
> focus behind the film plane by 0.2mm.
>
> Why then are many users of Hexar bodies with Leica lenses happy?
> Pick anyone of these explanations.
> One  happens to have a Hexar where the max tolerance all are in one
> direction, which might bring the effective back focus to about 27.90 and
> when stopping down or using a wide angle the difference is covered by
> DoF.
> The expectations about optical quality or the demands on the picture are
> quite low.
> The topics photographed are quite tolerant for uncritical focussing.
>
> I find it remarkable that this topic has not been discussed as it is the
> key to understanding the Hexar/leica compatibility issues.
>
> Erwin