Converting G Lenses to M mount?

Hacker said:
Unless it is for the fun and wow factor, the ZM series uses the same design, but in M mount.
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Nops. The ZM are different from the G lenses. Typically the G designs have a shorter back focus (distance last lens to film). In case of the 28 & 21 mm f/2.8 Biogons this results in higher distortion figures for the ZM designs.

The most dramatic difference is with the 35/2. This is a Planar in the G line and a Biogon in the ZM line. Here the ZM has the edge in the distortion department. Though the G lens is much smaller.

You can get very detailed data for these lenses from the Zeiss server:

http://www.zeiss.com/C12567A8003B58B9/Contents-Frame/3CFD45E4A65DEC10C12571000056AC85

http://www.zeiss.com/C12567A8003B58B9/Contents-Frame/3CFD45E4A65DEC10C12571000056AC85

Typically the G lenses are substantially smaller and cheaper to buy (even when they were still in production). Surely a hand crafted M conversion will take the price advantage away.
 
Timmy P said:
So the question is, has it been done with any G lenses? The Zeiss 45 Planar is an amazing lens, but it's a real shame it can only be used on G series camera's only. Has anyone ever heard of an G to M mount conversion, or if it can even be done?

Thanks for any help,

-Tim
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Tim:

I have had this done for a 45/2 Planar G-->M mount. The work was done by Hyata Camera Laboratories in Tokyo, Japan. Works great. Not cheap. It probably makes more pure financial sense for wides that are hideously expensive in M-mount to begin with. I was not motivated by the finances of the project though. I just love the Planar. My recent post (in the Off to Taipei with an M8 thread) is copied below.

>>>>

The lens is fully RF-coupled. After a little tweaking, focus is dead on at all apertures and distances. The conversion was done by Hayata Camera Labs in Tokyo, Japan. Actually, the process was a bit of a hassle, because Hayata does not ship outside Japan (or at least not to the US). I had to find a correspondent in Tokyo who was willing to act as a middleman. In the new mount, the lens back-focussed slightly. Rather than deal with sending the lens back to Tokyo, I had DAG tweak it. He did a great job and, for me at least, it has been worth it. The Contax 45/2 Planar is one of my all-time favorites. So much so, that I actually went looking for another on which to do the conversion. I found one for a very reasonable price from an RFF'er; however taking the expense of the conversion into account, you could certainly buy a 50/2 Planar for what I finally paid, all in. Still, I'd been hoping to do this for a while and so far have been very happy with the results.

Hyata, BTW has a web-page in Japanese and they seem to offer M-mount conversion for a range of lenses. Their work was of good quality -- because the original lens is autofocus, they had to create a manual focus helical and tube matched to the 45/2's focus characteristics. The aperture is non-click stop, but works. The final product looks a little bit like a collapsible lens that has been fully extended. FWIW, I had checked around with my favorite repair-people (DAG, Sherry) and machinists in the US and found no one who was willing to both take on the job and guarantee the results. Hayata has done hundreds of these conversions and although there is a hassle factor in getting the lens (and payment!) to them, I wanted someone to do the conversion who had been through the process before.

I'll post some pics at the end of April when I am back from my travels.

Ben Marks
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