Fix for front focus with Avenon 21/2.8

[pfogle]

I originally posted this on another thread, so apologies for the double posting, but I thought it might be of wider interest... the lens was focusing 8 inches in front at 6ft.

Here's the fix for the Avenon on my body... I used a fine (EE1 0) grit wet-and-dry on a mirror. Using a cheap dial caliper, I measured 0.98 mm at the start and 0.91 at the finish. In fact there was some variation around the rim, at the limit of what I could measure, maybe 0.02 mm. The attached pictures show how much the lens could screw into the adapter before I ground it and after. The angle of difference, 24 degrees, and the pitch, 0.75mm, gives a depth of 0.05 mm, which is pretty much what I originally calculated.

I think it's an under-correction, but since you can't put the metal back on, I decided to be conservative ;)

There's still a suggestion of front focus, hard to measure, but a definite improvement at infinity. As expected, the rangefinder now focuses past infinity, but only very slightly, and you'd never notice in practice.

All in all, it took about an hour.

One word of caution... be VERY careful not to get any metal dust in either your camera, or the focusing helicoid, which is very exposed on the Avenon. Please be careful here; I washed the adapter and dried it before each test.

Phil

[jlw]

I think it's an under-correction, but since you can't put the metal back on, I decided to be conservative ;)

Just in case someone else tries this and overdoes it: You can't put the metal back on -- but you could cut a ring-shaped shim and sandwich it between the lens and the adapter.

Brass shim stock is available at hardware stores in a variety of thicknesses. The thin ones cut easily with a pair of scissors.

[mtokue]

Wow. great,
I just wanted to say that it has/is a very uplifting experience, following/partaking in these threads, re: the Avenon/Focus/mount Adapter, the way that people from different continents have, without coertion come together and in essence formed Rangefinerforums very own
RD-1 R&D team!
Mike.

[Jim Watts]

I managed to try out 4 different screw to M adapters with the 21mm Avenon on my R-D1 at a camera fair on Sunday and purchased the best 2. One Leitz 28/50 and one Leitz 90. All of the four were slightly different with regard to close-focus amounts with the 21mm.

At home I have now tested and fine tuned the 3 adapters I now have to the lenses I use. The Leitz 90 has improved the accuracy of the Avenon 21mm over the the VC adapter that I was using before, not perfect but pretty close. The Leitz 28/50 is perfect with the 28mm VC Ultron and I have relegated the VC adapter to use on the VC 25mm Skopar which is not coupled to the rangefinder.