Minolta 90mm F4 m rokkor

[Bliz]

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A couple of days ago I bought a nice 90mm M rokkor f4 trying it on my m10r, where it works very well. Yesterday I tried mounting it on my m4 and noticed there the rf patch doesn’t align at infinity, while on the m10r it does and the focus is correct at every distance. Does anybody has an idea why? I can use it on the m10 and deal with it, but I’m still surprised since I thought the rf mechanism was pretty much the same among the various M bodies. Of course the m4 works well with my other lenses.

 

Edit. Sorry I thought I was in the m lenses section…

Edited Sunday at 11:29 PM by Bliz

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[adan]

3 hours ago, Bliz said:

I can use it on the m10 and deal with it, but I’m still surprised since I thought the rf mechanism was pretty much the same among the various M bodies.

Your experience of "works fine with a post-2017 M10, but does not work as well on a pre-1975 M4" is to be expected, at least for the 90mm focal length.

The "C" lenses for the film Leica CL and Leitz/Minolta CL were not designed the same way as most Leica-M lenses. They have a simpler focus-cam geometry (I won't get into the gory details unless you want) - to save production costs on that "discounted/cheaper" product line.

Even when they were introduced, Leica warned those lenses could be problematic if used on the main-line M cameras of that era (1973-76, which would include the original  M4 and M5). And the 90mm in particular, because of its higher magnification and narrower DoF, might be unreliable. At the time, many users confirmed such problems.

The 40mm companion lenses usually work(ed) adequately - less magnification, more DoF (usually), more leeway for focusing error.

Leica has reworked the M rangefinder several times since the 1970s - usually in minor details, but with a more substantial upgrade in the M10 (and M11). Which (by coincidence) makes the ancient "C" 90mm lenses often work well with more modern Ms (post-1980, post-1986 (M6) and even more so post-2017).

I have used 2-3 different 90mm C Elmars on my M10s - and they have focused quite reliably.

Edited Monday at 03:25 AM by adan

[Bliz]

5 minutes ago, adan said:

Your experience of "works fine with a post-2017 M10, but does not work as well on a pre-1975 M4" is to be expected, at least for the 90mm focal length.

Thanks for the very interesting informations, I'll just use it on the digital body or at infinity on film.

I'm curious, would it work on a current production film body?

Edited Monday at 03:28 AM by Bliz

[adan]

2 hours ago, Bliz said:

I'm curious, would it work on a current production film body?

I have no idea.  I hope so. Leica has been tightening tolerances all across its products with every passing year (and decade). That was one of the main reasons given for building the all-new factory in Wetzlar in 2014.

The essential problem is the tolerances for the left/right positioning of the camera's RF contact roller.

With M lenses on M cameras, that tolerance could have some leeway left and right, because the entire focus cam surface is flat and even. And that surface moving in and out on a helix thread, to move the RF images around, moves the RF roller. It does not matter where the camera roller makes contact with the lens cam.

With the -C lenses on the CL camera, with an entirely different RF, some money was saved by leaving out the cam's moving helix and and flat surface.

Instead, their cam did NOT move in and out and was NOT flat - it had a sloped or ramped surface that got higher or lower, rather than actually moving in and out, as the lens turned for focusing. And that required the lens roller to always be in the exact same place, in every camera that came from Minolta's factory.

The M camera rollers of the time did not need that left-right precision, so long as they used M lenses with the flat, wide cam surface.

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