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Are Leica M lenses compatible with the Konica Hexar RF?

Introduction

This is the infamous Hexar RF back-focus controversy which kept us distracted & amused during 2001-2.

In early 2001 there was a small amount of confusion, foot-stamping and panic when Erwin Puts reported on his Hexar RF page that his camera appeared to have a measured Lens-To-Film (LTF) distance of 28.00mm ± 0.03, slightly longer than the Leica M standard of 27.80mm ± 0.01. The implication being, if it were true, that the Hexar RF inherently gave inaccurate focus when used with Leica M glass. Yikes!

After a flurry of denial and abuse and "there's no problem with my camera" posts, over the course of a few months a general consensus developed that the difference may have been only due to different LTF measurement methodologies. Since the film pressure plates in the Hexar and Leica M are located at slightly different distances from the lens when the camera is empty, any attempt to measure the LTF will give you different results. Load the camera with film however, and in both cases the film front surface should now be at the required distance of 27.80mm ± 0.01.

At the time this seemed like a logical explanation and it indicated there was no problem with the RF's back-focus, provided you had film in your camera when taking pictures…

Keppler's Bombshell

There the matter rested until May 2002 when Wolfgang. A. Kuester sent me a photocopy of a letter from Mr Herbert Keppler, the Publishing Director of (US) Popular Photography Magazine. In it Mr Keppler presented the results of Pop-Photo's own measurements, which clearly confirmed Mr Puts 2001 back-focus-error warning.

After contacting Mason Resnick, the Managing Editor of the magazine, to confirm the letter's authenticity and obtain permission to reproduce its contents, I present a copy of it below, complete and un-edited:

April 30, 2002
 
Dear Mr. Kuester:
 
No doubt you probably decided that you would never hear from us concerning the variation in back focus between the Leica M series cameras, and the Hexar RF. Recently we finally got down to doing a test using a 50mm ƒ2.0 Summicron lens on the Voigtländer M body, the Leica M3 and the Hexar RF at 8 feet and ƒ2.0. We also had the back focus measured very carefully by a testing laboratory. We found that the back focus of the Hexar RF was 28.7 mm that of the Leica M 3 27.6 mm, and the Voigtländer 27.01 mm.
 
In examining the lines per millimetre resolution of the Kodak T-Max 100 film with the lens set precisely at 8 feet, we were able to produce 57 lines per millimetre at the center with the Leica M3, and the Voigtländer camera, but only 22 lines per millimetre with the Hexar. We therefore concluded that the Hexar lenses and cameras are not interchangeable whatsoever with the Leica M3 and the Voigtländer cameras. While it is possible that wide-angle Hexar lenses may indeed be useable, they certainly would not be our first choice, and certainly should be avoided for use on Leica or Voigtländer for normal focal length lenses or longer, and for large apertures. Hope this is the final word on the situation.
 
Best wishes,
 
Herbert Keppler

Important note: The contents of the above letter are the copyright © of Herbert Keppler USA 2002. Reproduction without the express permission of Mr Keppler and/or Popular Photography Magazine is prohibited. )

The End of The World?

Hardly.

(1) In May 2002 Dante Stella did his own research into the Hexar RF "flange" controversy and confirmed that there appears to be no problem with the LTF distance - see his detailed notes and conclusions at: <dantestella.com/technical/flange.html>

(2) In Aug 2002, Aric Rothman did some precise measurements of his own, also reporting no problem:

Using a vernier micrometric depth gauge, I measured the Lens Flange to Film (LTF) distances on my Leica M6 (classic) and Hexar RF. In both cases, a section of Fuji Neopan film was placed in position on the film rails and the cameras' backs were closed.
 
Each camera was measured four times, and the results averaged. The depth gauge accuracy was verified using a digital caliper.
 
The LTF of the M6 was 27.98mm. The LTF of the Hexar RF was 27.97mm.
 
What does this mean? I don't know. I do know that I have taken pics using a CV Nokton wide open on my Hexar RF with excellent results. I have also taken pics using M-Hexanon 50mm/2 and 28mm lenses mounted on both my M6 and HRF with excellent results.
 
My test results, admittedly of very small sample size, appear to be at odds with tests showing LTF differences between Leica Ms and Hexar RFs on the order of 1.8mm. […]

(3) We should not lose sight that only two cameras thus far have been measured with a significant LTF error - not two or twenty percent. Perhaps only early production runs of the Hexar RF are "out", with the problem fixed in later batches? We simply don't know.

On the other hand, although one bad LTF can be dismissed as crankish brand-zealotry, a pair of them appear suspiciously like a trend. As our academic friends like to say, "more research is required"…

Flesher's Work-around

During a June 2002 online discussion at <Photo.net: #003Pvm> about the Hexar RF's incompatibility problems, Jack Flesher noted the following "hack" to repair the Hexar RF back-focus problem:

Okay. It is really very simple. I am going to let everybody in on a little secret... Remove the four screws that mount the Hexar bayonet flange to the camera body, and CAREFULLY lift off the flange taking care to not lose the lens release button and associated pieces. Once off, you will notice four small shims behind each screw hole of the flange. Interestingly, each of these shims is about .2mm in thickness... Simply remove these and throw them in a baggie. Reattach the flange without the shims. Presto, you have recalibrated your Hexar's F-to-F distance so it now equals that of the Leica M.
 
Please notice that my method does no permanent damage to the Hexar, nor is it a "non-reversable" fix. I offer it simply for those that ARE experiencing problems with focus on their Hexar's.
 
[…] I discovered the shims when I took mine apart for a repair because I was having other problems with it. So, I have seen these shims with my own eyes, and they are very easy to remove and re-install if you have simple basic mechanical skill and as Paul points out, some manual dexterity. And the shims are small, and thin, and made of brass -- so they are not magnetic and you will need tweezers or forceps to handle them. The most difficult part of re-assembly is keeping the holes in them aligned with the holes in the flange and body while you re-insert the screws -- use a pin or toothpick for this purpose.
 
The HOWEVER BUT: I never bothered to actually test the camera with them in place vs removed, so I cannot claim any increase in performance -- I personally disliked the camera so much, I simply put them back in when I decided to sell it. Needless to say, removing the shims will indeed move the lensmount flange back toward the film plane by approximately .2mm if you think you have a problem with Hexar back-focus.
 
Lastly, I remain convinced that Konica put these shims there in the first place so they could claim back-focus incompatibility... after the fact.

Konica (UK) will fix-it?

In Aug 2002 Steve Patriquen sent me the following note:

[…] I have a Hexar RF that I purchased as a 'demo' from a HK seller on eBay. It's back-focus and the RF were off, despite it appearing to be brand-new. A trip to Konica UK with a 50mm Summicron (and a mere £ 140 later) and it focuses the 90AA/2 Leica wide open as good as a brand-new M7.

Food for thought - if Konica UK were prepared to adjust Mr Patriquen's camera without argument, then maybe there's something in the back-focus error claim after all!…

Mis-calibrated Rangefinder?

On top of the LTF controversy, a small band of Hexar critics also maintain that even if the LTF distance is okay, the rangefinder design and factory-calibration of the RF is typically out by 10%. One complainant has tested this and claims the 75mm Summilux wide open at 3m is sufficiently out for the resulting image on film to "lack micro-contrast and overall sharpness".

To this I say Reality Check. With that lens at the ƒ1.4 aperture setting, every single factory-calibrated rangefinder on earth will be slightly out as you only have a DOF of 10cm. If you want to use a rangefinder to focus with exact precision under such conditions, then you must not only use a higher magnification finder (M3, M6 0.85) but also have it custom calibrated for the specific lens you own. Out of the box, at such narrow extremes no rangefinder with an ERB of only 41mm will give you "micro-contrast" results.

Discussion Links

Hexar lovers (and haters) have repeatedly vented their pent-up frustrations ever since Mr Puts published his original "review". You can easily find them via a Google search. Here for example is one discussion thread:

Aug 2002, with new LTF "measurements":
<Photo.net: #003bWM>

A note about possible broken links

This FAQ has over 900 external links. Over time it is inevitable some of them will break. If you are bothered by this, see this detailed topic elsewhere in the FAQ.

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