Am I being unreasonable? (Zeiss Sonnar focus issue)

[ho_co]

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Gerry--I think EP gives the answer to your questions in his review of the 50/2 aspheric at Apo-Summicron-M 2/50 ASPH | The TAO of Leica.

 

Check out paragraphs 7-8, beginning "The classical benchmarks...."

 

Also, IMHO Leica has certainly tightened tolerances since the film-only days.

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[gyoung]

Yes thanks, I understand now, and the discussion of other considerations is interesting. When I started working in a photo shop after leaving school we had a device for testing collimation, this projected a pattern of green circles onto the film surface through the lens in question at a virtual infinity and looking through the eyepiece the sharpness of the circles on the film surface could be judged. It follows from that the ideal was that the collimation was considered correct if done on the surface of the film rather than at some point within the emulsion, and that would probably be best I suppose with a simple B&W emulsion, and would work with a sensor. There would have to be tolerances obviously and presumably its possible (as well as desirable) to do things more accurately now, even if the manufacturers don't actually achieve that sometimes.

Its also interesting to see the best that even the M will do is the equivalent of 80 lpm, so we are still not up to the capabilities of film.

Its easy to get carried away with the science of it all, we certainly have been getting 'sharp' pictures on film in spite of the limitations, and I suppose its unlikely to be useful to photgraph a person at close distances with such a wide aperture that eyeballs are sharp and eyelashes less so

 

Gerry

[wlaidlaw]

Zeiss used to be fanatical about film flatness. The later RTS cameras had a vacuum pump and a perforated ceramic pressure plate, to suck the film flat just before the image was taken. We were told at a meeting for the UK Contax beta testers, that fairly early in the life of the Kyocera-made cameras, Zeiss decided to go 100% motor drive, not principally for convenience of use but mainly to control film tension and curvature.

 

At least Leica have got rid of the bed sheet with the cross on it, which they used to use for focus testing. I think they now use a Zeiss computerised dual slit interferometer. There was certainly one, half hidden under a dust sheet, when I was last in Solms.

 

Wilson

[algrove]

Anyone have an idea how to TALK with someone at Zeiss about whether a certain 1.5/50 is optimized for 1.5 or 2.8? I have spent about 2 hours getting shifted to the wrong people and am fed up with it. Would like a phone number or failing bthat a web address for questions. My lens box has a blue dot on the bottom of it where the lens serial number is located on the outer box (no other Zeiss lens box I have has a dot on the bottom of it and I have 3 others) which maybe indicates something.

 

Thanks for any assistance.

[wlaidlaw]

Having dealt with Zeiss over a number of years, as a Contax Beta tester, they are a weird company. The only way I think you will get an answer is to feed it via a friendly dealer. Nobody seems to stay in the same job for more than a few months and just when you think you have built a relationship, away they go to a different job, which is not relevant to what you want to discuss.

 

Sorry not to be of more help. Thinking about it, you might have more luck addressing the query to Cosina, who actually make the lens (I think only the 85/2.8 and 15/2.8 were made in Germany).

 

Wilson

[chalkdust]

algrove, I had the same question about my ZM Sonnar. Because I inherited it from my father, I did not know whether it was optimized for f/1.5 or f/2.8. I put it on my M8.2 and tried several different shots of a ruler on a table at a bit more than a meter distance. It was easy to see from the results that mine was optimized for f/2.8. It showed several inches of front focus at f/1.5. If you have a digital body, this is a simple and rapid test. I have worked hard at estimating the front focus correction for wide apertures and can now obtain good results. The effort was well worth the time spent.