M-Rokkor 40mm f2 (version 2) disassembly help

[happy]

Hi all,

I am experiencing some minor front-focusing with my M-Rokkor 40mm (CLE version). About one inch or so at minimum focus, but visible at all close and medium distances. Infinity focus seems okay, but DOF might be covering it. Otherwise, this lens is absolutely incredible.

There is a little bit of 'wiggle' in the focus ring. I was hoping to take the lens apart to tighten everything down and see if it fixed the issue. Otherwise, I don't mind shaving down the shim (or abrading) by just a hair to fix it.

I have tested another lens, a 50 summicron rigid, and it was spot on. I'm fairly sure it's the lens. At any rate I'd like to get things cleaned and tightened down.

Anyone with experience taking this lens apart? Any tips? I imagine the first step is to remove the retaining ring (the one with circular holes) on the back of the lens with spanners to detach the optical assembly from the helicoid assembly. Please correct me if I'm wrong.

Thanks!

 

[ferider]

I wouldn't fix it. 1 inch front focus in the center at min. focus is perfect for a 40/2 to compensate for the cosine effect. Try to focus and recompose, and read this, for instance:

http://www.rangefinderforum.com/forums/showthread.php?t=148485

Regarding the wiggle: the CLE Rokkor has the mount integrated with the focusing helix. Take the mount off (remember when/where the helix pops out), clean and re-grease, and put the mount back on. That should eliminate the wiggle (it did in my case).

Roland.

 

[happy]

I wouldn't fix it. 1 inch front focus in the center at min. focus is perfect for a 40/2 to compensate for the cosine effect. Try to focus and recompose, and read this, for instance:

http://www.rangefinderforum.com/forums/showthread.php?t=148485

Roland.

This is some interesting food for thought 🙂

Thanks for the tip on fixing the wiggle!

Eventually I'd still like to crack this open. Part due to my curiosity but I'm also interested in changing the focus tab to a custom concave indented tab like on the Summicron 35.

 

[f16sunshine]

Hi all,

I am experiencing some minor front-focusing with my M-Rokkor 40mm (CLE version). About one inch or so at minimum focus, but visible at all close and medium distances. Infinity focus seems okay, but DOF might be covering it. Otherwise, this lens is absolutely incredible.

There is a little bit of 'wiggle' in the focus ring. I was hoping to take the lens apart to tighten everything down and see if it fixed the issue. Otherwise, I don't mind shaving down the shim (or abrading) by just a hair to fix it.

I have tested another lens, a 50 summicron rigid, and it was spot on. I'm fairly sure it's the lens. At any rate I'd like to get things cleaned and tightened down.

Anyone with experience taking this lens apart? Any tips? I imagine the first step is to remove the retaining ring (the one with circular holes) on the back of the lens with spanners to detach the optical assembly from the helicoid assembly. Please correct me if I'm wrong.

Thanks!

I have taken a CLE version apart. My recomendation is you don't do it. Send it to DAG if you feel it needs a tune up.

The actual M mount of this lens is one half of the Helicoid thread. If you mess it or miss alaign it, you will have a very difficult time getting it back in order.


The lens is an absolute gem. It's easily worth a $100 spa visit to Don. He'll send it back better than new 🙂

 

[ferider]

Eventually I'd still like to crack this open. Part due to my curiosity but I'm also interested in changing the focus tab to a custom concave indented tab like on the Summicron 35.

Makes sense. Start from the rear.

Note that - once off - the mount is difficult to align and put back on - you have to be patient (and don't blame me 🙂 ).

This is one of the best Leica mount lenses ever ! (google "Water Lens", for instance - color rendering, resolution, bokeh are all quite special)

 

[happy]

I have taken a CLE version apart. My recomendation is you don't do it. Send it to DAG if you feel it needs a tune up.

The actual M mount of this lens is one half of the Helicoid thread. If you mess it or miss alaign it, you will have a very difficult time getting it back in order.


The lens is an absolute gem. It's easily worth a $100 spa visit to Don. He'll send it back better than new 🙂

Hey, a fellow Seattleite!

So did you manage to get it back together?

I've taken apart rangefinder lenses before and they're fairly simple... Generally everything is locked in and secured so it's just a matter of reassembling things in the right order, at least for the older lenses with simpler designs. I figure if I can spend an afternoon getting acquainted with this lens I can at least figure out how to solve the issue and whether or not it's worth it.

I've heard nothing but good things about Don and I've spoken to him over the phone before. However, I enjoy tinkering and I don't want to be without my lens for four weeks (it's my only M lens right now)... I agree $100 bucks is next to nothing in the camera world 😀

 

[f16sunshine]

Hi Happy.. nice to see you too.

I actually did get it back together but could not get the helicoid aligned (even though I matched my marks.
I sent it firt to Youxin. He could not get it. I then sent it to Don. He got it!
Now it's perfect. One of my all time fav lenses!

One of my favorite images taken with it.

 

[happy]

Hi Happy.. nice to see you too.

I actually did get it back together but could not get the helicoid aligned (even though I matched my marks.
I sent it firt to Youxin. He could not get it. I then sent it to Don. He got it!
Now it's perfect. One of my all time fav lenses!

One of my favorite images taken with it.

question: When you say you couldn't get the helicoid aligned, do you mean that you were off by a thread in one direction or the other? I imagine that once you get the helicoid threaded into the proper slot, the alignment should be fine, no?

 

[happy]

Opened her up, was no problem at all. I'll document it with some pictures because I haven't found anything online referencing disassembly of this lens.

I did some testing with the tangential 'focus recompose' shift and the 1 inch front focus is a little bit too much unless I recompose my subject to near the edge of the frame. I think 1/2 inch or 1/4 inch front focus is more appropriate for this focal length on my M8.

Nothing really seems adjustable inside the lens so I will be shaving the shim. What's the math on how to figure out how much of the shim to remove? I have access to a machine shop but if it's small enough of an adjustment it may be safer to use an abrasive. Otherwise I will have to do by trial and error.

First, I will test a couple other lenses just to be extra sure this is a lens issue. Will update.

 

[ferider]

I did some testing with the tangential 'focus recompose' shift and the 1 inch front focus is a little bit too much unless I recompose my subject to near the edge of the frame. I think 1/2 inch or 1/4 inch front focus is more appropriate for this focal length on my M8.

Makes sense, I didn't know you were using an M8. Then again, before you modify the lens, check out f2.8 and f4 as well (shift), and think about it.

....What's the math on how to figure out how much of the shim to remove? I have access to a machine shop but if it's small enough of an adjustment it may be safer to use an abrasive. Otherwise I will have to do by trial and error.

First, I will test a couple other lenses just to be extra sure this is a lens issue. Will update.

You can see the math applied here, happy: http://www.rangefinderforum.com/forums/showthread.php?t=151300

Basically you follow 1/f = 1/o + 1/i, where f is the focal length (40mm), o is the object distance (for example 800mm min. focus for the Rokkor), and i is the image distance, which is, for example, 40mm for o = infinity.

You will have to remove very little, so a grinding stone or fine sandpaper should be the right tool.

Roland.

 

[Brian Legge]

Funny timing. I just cleaned a M-Rokkor 40/2 a few weeks ago. There is still a little haze between front elements but its much, much better than it was previously.

The construction of the lens is very similar to Canon LTM lenses for anyone who has worked on them. There is a rear retaining ring in the back which separates the mount/helical from the front element assembly. The helical itself is fairly simple. Over all, anyone who has worked on a Canon LTM lens has a good shot at lubrication and cleaning between the elements.

That said, I think I spent about an hour on the helical, getting it back in to the mount and all. 🙂

 

[f16sunshine]

Funny... That said, I think I spent about an hour on the helical, getting it back in to the mount and all. 🙂

See me too !
I got scared and quit... Then more scared when YY sent it back 😛
Good thing DAG is there for clean up crew!

Nice work sorting it out Happy.
I hope you did a little tutorial 🙂

 

[k__43]

Hi - have you actually checked the lens on another camera?
Or maybe another 40/2 on that camera. (I remember you said it was ok on other cameras, right?)
As I tried to explain in your other threat, the cam of that particular lens is more prone to a maladjusted focusing arm length.

I would definitely double or triple check before taking apart a lens further than dividing it in lens and focusing part.
Please excuse me if you already did that - good luck with your fix then!

 

[happy]

Hi - have you actually checked the lens on another camera?
Or maybe another 40/2 on that camera. (I remember you said it was ok on other cameras, right?)
As I tried to explain in your other threat, the cam of that particular lens is more prone to a maladjusted focusing arm length.

I would definitely double or triple check before taking apart a lens further than dividing it in lens and focusing part.
Please excuse me if you already did that - good luck with your fix then!

Hi there.... I will definitely do further testing to make double sure it's the lens. However this is a different lens than what we discussed a few weeks ago... I was referring to a Summicron-C in the past thread and this new lens is a Minolta CLE version with the flat cam... no sloped cam on this lens! So the rangefinder arm length should not be an issue.

 

[k__43]

Hi there.... I will definitely do further testing to make double sure it's the lens. However this is a different lens than what we discussed a few weeks ago... I was referring to a Summicron-C in the past thread and this new lens is a Minolta CLE version with the flat cam... no sloped cam on this lens! So the rangefinder arm length should not be an issue.

oh, I did not know that (the CAM fact)!
just interesting tho how two 40/2 lenses fail on your M8. Maybe it's the universe's way of telling you to use another focal length 😛

 

[k__43]

now I have been thinking for the last 15 minutes hwo the f&%k they manage to translate the focus movement of the 40 into a 51.3ish RF coupling when it's not a sloped cam and the lens didn't grow much either. can someone enlighten me here please?

 

[happy]

There are two versions of the rokkor: one has the same sloped cam mechanism as the summicron-c and the newer CLE version has a double helicoid. they managed to keep it the same size!

 

[happy]

My LORD you guys weren't kidding about the helicoid. The first one wasn't so much of an issue but as I was trying to clean/grease the outer helicoid, the INNER helicoid fell out! With no markings to help me. Getting it all back together lined up with the right threads was a harrowing experience.

I should make a "I survived the helicoid experience" T-shirt

Now the lens is back together and lined up (and still front focusing by an inch). But with all I've done the focusing ring has gotten noticeably stiffer/less smooth. I'll have to open her back up and properly clean/lube/reassemble the helicoids when I have a free afternoon.

Any suggestions on grease? Looks like there was a petrolium grease on the outer helicoid and a graphite grease on the inner? I'd appreciate some input.

Working on a mini repair guide for this lens in the meantime.