180mm Sekor KL infinity focus problem with RB67 Pro SD

mdanie789 · Dec 26, 2014

Hello everyone - first post.

I have an infinity focus problem with a 180mm Sekor KL with RB67 Pro SD. The lens seems to be set to a maximum focus distance of ~10m (30ft) with bellows racked all the way back. I have checked: the same issue on a separate RB67 SD body and at the film plane (excluding focussing screen issues), and also verified that another photographer sees the same problem. Other lenses in my collection are fine, and the 180mm is probably the least-used lens I own - suggesting it has not suffered any abuse before I bought it (secondhand from Japan). It focusses fine at short distances.

I'm wondering whether there is any possibility of adjusting the lens (older lenses used internal shims to set infinity with a collimator) ........ and how (preferably without much expense)? Also, is there any precedent for such lenses to be set to closer focus deliberately eg. portrait photographers wanting to start with a 10m focussed distance/zero bellows?

Many thanks if anyone can shed light on this or has experienced the same problem.

Kirks518 · Dec 26, 2014

Well, you made me look.

I have the same camera, and a 90mm, 180mm, and 250mm, and all focus just fine at infinity (or at least the moon). Using my 2x TC though, I am just this side of focused at infinity.

As far as correcting it - I'm of no help to you.

Trail Images · Dec 26, 2014

180mm Sekor KL with RB67 Pro SD

Are the other lenses all KL too?....just thinking out loud about the collar or spacer used on earlier lenses when using the SD body. Not sure that would have a bit of issue here. I have the SD and 180 non KL and use the collar. Seems to work fine at infinity on my rig.

shutterfinger · Dec 26, 2014

Its been a long time since I worked on a RB lens and they weren't KL. The lens elements/groups should screw in and snug against a stop. Start with the rear element and verify it is screwed in against the stop. It should have slots for standard lens spanner wrench. The front is a different story, it has a retaining ring at the front edge and the center element position affects the front position.
If the focus is good from 30 feet down to the closest the camera bellows will allow then the front and center are probably correct. If the rear is snug against its stop then loosen it in steps and check the effect on focusing. 1 minute on a clock face is 6°. Also remove the rear element and look for debris in the threads that may be causing it not to seat properly. If there are shims between the rear element and the mount remove them 1 at a time and evaluate the focus change if backing the lens element out does not solve the problem.

Kirks518, check the cells of your TC, if one or the other is off 1° of a turn it will result in the focus error you have. 1 turn = 360°.

tkamiya · Dec 26, 2014

I have an RB-SD and 180mm/KL right here.

One thing to note is that some lenses in RB series does NOT infinity focus at belows racked all the way back. Some has to extend the belows just a little. Put it other words, belows movement goes beyond infinity (sort of speak....) In fact, mine is that way.

So try that first.

Looking at similar setup, focused at infinity, the closest I find sharply in focus is about 10 meters away. (I didn't actually measure.... guessing here) But, infinity object is also sharply in focus. You are saying yours is not?

mdanie789 · Dec 27, 2014

Thank you everyone for your comments and suggestions (just read them). Last night I took the plunge and began dismantling from the rear. The lens had definitely been tampered with as the rear element was the wrong way round! (http://rb67.helluin.org/lenses/kl-180mm-f4-5l-a/ for figure). Having re-seated the shims on the rear of the shutter (I don't believe these affect element spacing) and reassembled as carefully as possible, I'm delighted to report correct infinity focus at minimum bellows extension now . Once again, thanks to all.

Kirks518 · Dec 27, 2014

Awesome you got it corrected!

Sanju Mathew · Jul 18, 2020

shutterfinger said:
Its been a long time since I worked on a RB lens and they weren't KL. The lens elements/groups should screw in and snug against a stop. Start with the rear element and verify it is screwed in against the stop. It should have slots for standard lens spanner wrench. The front is a different story, it has a retaining ring at the front edge and the center element position affects the front position.
If the focus is good from 30 feet down to the closest the camera bellows will allow then the front and center are probably correct. If the rear is snug against its stop then loosen it in steps and check the effect on focusing. 1 minute on a clock face is 6°. Also remove the rear element and look for debris in the threads that may be causing it not to seat properly. If there are shims between the rear element and the mount remove them 1 at a time and evaluate the focus change if backing the lens element out does not solve the problem.

Kirks518, check the cells of your TC, if one or the other is off 1° of a turn it will result in the focus error you have. 1 turn = 360°.

Hello there
I saw your suggestions regarding the 180mm infinity focus issue, I would like to know your thoughts on replacing the elements from a donar lens to the new one, recently I was having an issue with one of the Mamiya Rb 67 127mm 3.5 KL lens, it had the front element damaged, i managed to find a donar lens and replaced both front and the back groups all looks fine so far but I was wondering when I dismantled the donar lens assembly I noticed there was 4 adjusting shims (the shims in between the shutter and the rear assembly) but the receiving lens only had 2, do you think there will be any issues with infinity focus?
Very much looking forward to hearing back from you.
Many thanks
S Mathew

180mm Sekor KL infinity focus problem with RB67 Pro SD

Privacy & Transparency

Privacy & Transparency