Kobalux 21mm frontfocus

[laptoprob]

After doing the wide-angle test I tried a (close)focus comparison of the Kobalux 21mm and the CV21/4. And found out the K shows pretty severe frontfocus. About 15cm at its closest distance: 1m.
Now if there would be a shim inside that could be replaced with something thinner there would be no problem. But there is nothing. The mount is screwed directly onto the lens body.
There is a small collar on the lens mount that can perhaps be milled off.

Anyone have experience with this one?

 

[laptoprob]

Found some older threads through google. I could shave a little off of the internal black body ring or shave a little off of the adapter. Other adapters gave similar results with the R-D1.

 

[Krosya]

I've had Kobalux 21 second version and now have Avenon black - last version 21mm and never notices any focus problems with either. I'll try to run some tests this weekend and see.

 

[akalai]

I found that critical focusing was dependant on what LTM -> M mount adapter was used with this lens.

I started using my Avenon 21mm (Mk.III) on a Bessa T with a Leitz 50mm LTM adapter but found it was front focusing. The easiest solution to the problem was finding and using an original later version of the Leitz 21 - 35mm LTM -> M adapter with the cutout section at the bottom of the mount.

The problem lies not only in the thickness of the LTM adapter, especially critical for wide angle lenses, but also how the lens sits once mounted.

There is a better description with some images showing the variation of how the lens sits with different adapaters here;

http://www.rangefinderforum.com/forums/showthread.php?t=5732

 

[Krosya]

I only use Leica original LTM->M adapters and they always seem accurate with any lens I tried. I once had original Kobalux 21mm one (with Kobalux 21mm lens 21 ) and that was fine too. However some aftermarket and CV I tried were not very accurate. So I stay with Leica ones since.

 

[laptoprob]

There is a better description with some images showing the variation of how the lens sits with different adapaters here;

http://www.rangefinderforum.com/forums/showthread.php?t=5732

Sadly the photos in that thread are gone. I will try my various adapters. I don't want to shave anything off in the lens, because of the almost guarantee of getting material in the helicals.
Just tested the lens with a 90mm Leica adapter and the CLE, seems fine. Judged with a SLR focusing screen.
FWIW, My Kobalux has no number, all there is on the front is: is M-series SUPER WIDE, L21:2.8 and Japan. All aluminium/white and six blades and black hood. Is this the second version?

 

[akalai]

Rob, some of the photos are missing which IS a shame.... but the photos that are posted along with the description given (if you read down further) should give you an idea of what is being explained.

Also if you use the Wayback Machine (Internet Archive) and plug in "Kobalux.com" you will get;

http://web.archive.org/web/*/http://Kobalux.com

...here you can view the various cached pages of the Kobalux webpage which might have some useful information to you.

Also there is a pretty good page on this lens at Cameraquest;

http://www.cameraquest.com/koba21.htm

 

[laptoprob]

M-series

M-series

Well, I didn't get a lot oout of the wayback machine. Most of the info on the web I've already seen I think. I am still puzzled about my Kobalux. M-series but not the 3rd generation.
I will sand down an adapter to make the lens work properly on the R-D1.