Experiences with Repro-Claron 355mm

I recently acquired a used 355mm f/9 Repro-Claron from

Schneider-Kreuznach in a Compur 2. According to Schneiders serial no.

list, it was made in the 1964-1965 time frame. As a process lens

with 4 lenses in 4 groups it is similar in construction to Apo-Artars

or - Ronars. Both lens and shutter are in very good condition and do

not look like its an aftermarket adaptation of a process camera lens.

When I tried it out, I noticed that the ground glass image wide open

was fuzzier than I would have expected from this type of lens and that

the lens showed _significant_ focus shift, about 1.5mm going from f/9

to f/22. Some test shots showed the same effect. The lens is

reasonably sharp when focused and used at f/22, although not as good

as a newer 240mm Apo-Ronar and 300mm Apo-Germinar I compared it to.

Interestingly, the focus shift required a reduction of the distance

lens-film when stopping down, which would suggest that the spherical

aberration is _over_corrected for the marginal rays.

Since dialyte type lenses like this are not really known for being

prone to focus shift (and my 240mm and 300mm don't show it at all), my

question: Has anybody else used this lens, or other Repro-Clarons

(_not_ a G-Claron, which is a plasmat-type lens), like the 210, 305,

or 420mm Repro-Claron? Experiences? Is this the way they are, or did I

just get a flawed one?

The repro-claron was only available in a barrel mount with no shutter, to the best of my knowledge.<br>From your description, I'd strongly suspect that someone has altered the correct spacing between the front and rear components of your lens, by inexpertly fitting it into a shutter.<p>The lens should be acceptably sharp wide open, and no process lens should show a focus shift on stopping down, since many process and copy cameras were focussed by setting the distance of the lensboard and the copyboard on a finely marked track, and not by visually examining the image.

I have a 420mm in a copal 3 made in 1970. My lens has no focus shift and makes sharp images. Your lens may not have been spaced correcly when put into the shutter. I would Contact Mr. Grimes for his advice.

 

Best Regards,

Robert

Pete and Robert, I think you are right. I had dismissed the possibility of a wrong cell spacing for the following reasons:

 

a)According to a post on usenet by Kerry Thalmann, 355mm Repro-Clarons (as well as 360mm Apo-Ronars) were actually sold in Compur 2 in the 1960's (make a search for Repro-Claron and Compur on Google groups).

 

b)The lens cells themselves are original (the negative inner lens is part of the mount and seems to be glued in, or at least the black edge paint covers both lens edge and part of the mount) and the threads on the shutter don't have any additional spacers or adapter rings and are part of the shutter front and back plates. Everything looks original.

 

c)I have an Apo-Germinar 300mm with the additional factory-made washer to change the spacing for optimization for infinity (the spacer is about 0.7mm thick). There the effect of that washer on the quality is rather subtle and only visible in the edges.

 

However, after reading your responses I rechecked and recognized that the front thread looks longer and further away from the stop, and remembered that a symmetric process lens should of course be symmetric about the stop. I used a marked thin strip of paper to estimate the distance from the diaphragm to the inner lens surface of each cell (very carefully), and yes: the distance is roughly 5mm for the back cell and 10mm for the front cell. Huge difference! So my guess is that either the cells came from a process lens after all and just happened to fit the shutter threads without modification, or the original no.2 shutter was exchanged with another one by somebody (there is a remark on Steve Grimes' web site that Compur 2's came in a variety of measures).

 

I guess the next step is to contact Schneider to get the original spacing and then have Steve Grimes get the lens back to those measures.

Thanks for the help!

One additional information on the lens, not really related to the above discussion. The front and back elements (the positive biconvex lenses) are discoloured to a slightly yellow-brownish color. As discussed for the Aero-Ektars elsewhere in this group, this is supposedly due to the effect of radioactive material, most probably thorium oxide, in the lens itself. We have an older counter here in the lab, and yes, the Repro-Claron is slightly radioactive. The meter showed about 300 Becquerel over background when put next to the lens (which is a comparatively small amount).