I have found that with wide angle MF lenses you can't get the best performance out of them unless the focus is bang on infinity - even stopped down. The focusing screen is rarley good enough to judge this so various tests looking at 100% crops on screen are the only way. I've adjusted the infinity stops on CZ 28mm F2.8, 50mm1.7 OL 35mm shift's ( and a few others) so I can get an exact match with each adaptor. Then the adaptor stays on that lens. WIth my new Elmarit 28mm the lens focused a bit past infinity (no suprise as both my other leica R's do with Roxen adaptors). If you want to DIY yours - here's how; Remove the front ring with the lettering on it using a friction cone. Then with a key wrench remove the locking ring that holds the front lens shroud on. Under this there is a larger lock ring that locks the focusing ring to the inner focusing helical - simply loosen this and manipulate the focus stop until perfect infinity is at the limit. The whole lens group moves as one unit so there is no upsetting the optical balance. Simple - but please use the right tools ( available from microtools). With this fixed I can now do a proper comparison between this and my CZ 28mm 2.8 - well I could have done if the sun had not gone in.

Gutsy move, shirozina, and not for the faint of heart for sure. Could you explain how you did it for the Zeiss 28/2.8?

Edited by StevenPA on Dec 04, 2007 at 12:01 AM GMT

Grab the front of the lens forward of the focusing ring and simply unscrew the shroud - it may be a bit stiff. Looking down the side you will see 3 screws - these clamp the focus ring to the inner focus helical. Loosen these and manipulate the focus point - this involves a bit of practice but the principal becomes evident. Getting the focus spot on with this lens means that in the central area there is no sharpness to be gained from stopping down - it realy is razor!

So the lens will unscrew into two pieces then, or will the inner section holding the lens elements just slide out only so far and expose the adjustment screws?

The lens elements stay put - this picture shows what should happen and I've arrowed one of the screws.

Thx for the photo. I don't own any Contax mount lens but it is interesting to see that it looks identical to my Flektogon 20mm 2.8 lens from the 60s.

They are also very similar to my Hassleblad lenses externaly - but quite different internaly.

Aha, I think I would have needed the pic to understand. Thanks, it's something to keep as a reference for the future.

Great thread! Thanks!

I have just recently been delving this deep into some of my alternative lenses. This weekend I had my Rokkor 45/2 completely disassembled to move the inner portion of the helicoid further back in the barrel, so the element assembly moves back further at the infinity setting. Quite a bit more involved than what you describe here. Glad to know they aren't all as complicated as the Rokkor.

I've not described resetting the Leica's multi start helical thread on another start point to eliminate a flat spot near infinity before I got round to adjusting the infinity stop. These lenses are a joy to work on as they are so precise and well engineered.

I can't wait to see the results

cogitech wrote:
Great thread! Thanks!

I have just recently been delving this deep into some of my alternative lenses. This weekend I had my Rokkor 45/2 completely disassembled to move the inner portion of the helicoid further back in the barrel, so the element assembly moves back further at the infinity setting. Quite a bit more involved than what you describe here. Glad to know they aren't all as complicated as the Rokkor.

Setting the focus on Contax lenses we discussed a lot a year or so ago. The small primes have two ways to adjust infinity, some use one, some use th other.

The first is one shirozina discussed, removing the front.

The other is removing the rubber focus grip and there are three small screws, loosen slightly and rotate as needed.

The lenses I have that work with one of these methods are:
- 28/2.8
- 35/2.8
- 50/1.4
- 50/1.7
- 60/2.8 S Planar
- 85/1.4

There may be others - but only lenses where all the elements move as a group.

Rodney

The olympus lenses seem to favour the grub screws under the focusing grip - it's the easiest type to adjust as you don't have to dismantle anything.