Cosina Voigtlander Lens Adjustment

[jdos2]

So.

I returned a lens and it was "sent to Japan" for adjustment.

I finally (> 2 months!) got a "replacement" lens back, and it's just as bad as the lens I sent in. I have some suspicions...

The upshot: I want to have my 40mm f/1.4 adjusted. It backfocuses. I can make it work with electrical tape on the focusing tab of the lens (really, a focusing ring) but of course, that's not optimal, and a lens that's .2mm out (the thickness of electrical tape) is WAY out. I don't want to wait "6-8" weeks, only to have to call to remind 'em to return the lens to me.

I'm certain that the lens is the problem. My 90mm Summicron focuses fine. My 50mm Summicron focuses fine. This lens doesn't work on the M8 at the local camera store either: backfocusing.

So? Anyone out there with a set of lens wrenches and an itch to look inside this beast? I had similar problems with my 28mm, but managed to fiddle with it (with a friend's help) and get it "close enough." I can't do that with this lens.

I sent a note to Sherry, but she didn't answer back (and I've yet to call).

 

[ferider]

How does it look at infinity, how far is it off at f1.4 and 0.7m,
and on which camera ?

Roland.

 

[jdos2]

How does it look at infinity, how far is it off at f1.4 and 0.7m,
and on which camera ?

Roland.

The lens has a linear error.

At infinity, the rangefinder lines up, but the images are slightly soft- brought into focus by turning the focus ring closer. Easily demonstrable. The lens is focusing past infinity.

At close focus, off by perhaps 3cm. Focus on the close eye at a few feet, and the far eye is in focus (and that's the problem: focus on the eyes, and the front of the ears are in)

Again, it's linear, so the tape does a pretty good job of reigning in the error. Lens now reaches focus on the rangefinder before it hits the stop. I'll not talk about letting the lens sit in the same position for too long- as the tape slowly thins... It's non optimal!

Finally, (and another edit to answer the question) this is on my, and the local photo shop's M8.

 

[ferider]

Hmm, that's not a lot.

3cm at close focus is pretty close to the lens' DOF. Note how very
short the Nokton's focus throw is (which is why there is no
1.4 mark on its DOF scale).

I have two Noktons and several M bodies. What you observe
happens to me, too, depending on which lens I use on which
(M3) body.

Also, similar for my 1965 90/2. Note that the 90/2 at 1m has very similar
DOF as the 42/1.4 at .7m (around 1-2cm on 35mm film, less on the M8).
All my M bodies have been CLA'ed in the last 3 years and so has been
the 90/2.

The way Don explained it to me, it can happen that camera and lens
are within spec, but the combo causes what you observe.
If I were you I would adjust the camera's RF roller a tenny bit, adjust
infinity to minimize the error for both 90/2 and 40/1.4 together.
Then leave it at that.

BTW, you might observe a similar difference for
some CV LTM adapters when compared to Leitz adapters.

Sorry, I don't have a better answer.

Roland.

 

[jdos2]

But it's not within the lens' DoF- and it's not only obvious, but correctable by moving the focusing flange .2 MM, that's 200 mills, closer to the camera- on this particular lens, that's something like .16 too far away from the sensor. 3CM is a VERY FULL 3CM- aft of where I put the focus. It's obviously out, and I'd like it adjusted, or I'd like to do the work myself.

That's why I'm asking around for an adjustment. If the lens could be used at infinity, I'd have figured I got a bad helical, a lens that wasn't really 40mm, or a combination of the two, but again, it's soft at infinity, focusing past that point.

I'd just like to know what I have to do to adjust the durned thing.

Can anyone suggest someone to adjust it? Sherry, as I said, doesn't seem interested.

Otherwise, the electrical tape will stay on it, and it focuses "well enough" with that. It's a very sharp lens with very nice drawing when in focus!


Thanks for the replies!

J

 

[clintock]

The lens has a linear error.

At infinity, the rangefinder lines up, but the images are slightly soft- brought into focus by turning the focus ring closer. Easily demonstrable. The lens is focusing past infinity.

At close focus, off by perhaps 3cm. Focus on the close eye at a few feet, and the far eye is in focus (and that's the problem: focus on the eyes, and the front of the ears are in)

Again, it's linear, so the tape does a pretty good job of reigning in the error. Lens now reaches focus on the rangefinder before it hits the stop. I'll not talk about letting the lens sit in the same position for too long- as the tape slowly thins... It's non optimal!

Finally, (and another edit to answer the question) this is on my, and the local photo shop's M8.

If the lens focuses past infinity, try taking the back most part of the mount off and shimming between the mount and the body of the lens.. that will bring the lens out slightly. The shim thickness between the mount and the lens body will have the effect of turning the focus ring to a closer setting..
Brass shiim stock from a machine shop supply would serve more permanently, or perhaps some other household materials.
The confusing thing is how you put tape on the part of the lens that presses against the RF arm, I think that would make the dissagreement worse between the RF and the focal plane. Good thing you have the digital body to use to check.
Maybe once you have the mount off you can find some kind of adjustment in there...
I wish I could help more, but that's one of the few CV lenses I don't have..

 

[Stu W]

Here is an old thread where Peter figured out how to adjust ltm mount VC lenses. There were shims under the mount. Could there also be shims under the mount of the 1.4? Stu
http://www.rangefinderforum.com/forums/showthread.php?t=14413

 

[jdos2]

My thinking went:

The lens has to reach infinity before the lens stops turning. The tape will force the rangefinder to indicate infinity BEFORE the lens reaches the stop, hence I'll stop turning it, and it'll stop retracting.

A shim will indeed affect the lens, but this isn't as good a solution because the rangefinder cam on the lens will also move out, meaning that the lens will stop turning before it reaches infinity on the rangefinder, bearing in mind that the rangefinder does reach infinity with this sample: the optics themselves focus beyond infinity at that point (without the tape, of course!)

If I could move the optics farther from the film plane by 40/50x.2mm (the ratio of a 40mm lens over the 50mm "uncammed" leica standard times the correction factor- the thickness of the electrical tape) without moving the cam on the lens, it'd fix it.

Now I just have to figure out how to do that.

Spoke with Sherry. She recommended I try the lens on a film camera, as well as another tech. Thank you Sherry! She suggested that the M8 is different enough from film that she's not going to play with digital.

And again, thanks for the responses folks!

 

[jdos2]

DAG'll take a look at it.

🙂

 

[davidzapr]

I just re-read Sean Reids review on this lens and in it it seems to be in focus at 1.4...then progressively gets more back focused as you stop down. Could this be an optical issue of the design?

 

[jdos2]

That's not surprising to me: that the lens suffers from a stop-down focus shift.

I spent some time after posting this string last night with the M8 on the tripod. I practiced getting the 90mm to focus exactly where I put focus, and did the same for the 50mm Summicron. I got the camera to focus precisely with the 90mm, and 50mm lenses, and then...

I tried the 40mm Nokton. I'm certain of the back focus wide open, and more like 5cm, or two inches worth at close focus. At "two head" distances, it backfocuses to ears. Infinity, it's most certainly beyond. The electrical tape I have at home is slightly different than the brand we have a the bicycle store, and slightly thicker, and offers too much correction, so I'm either going to have to work with that (thin it out a bit) or just let the focus cam do the work for me. Right now the lens (corrected with electrical tape) focuses slightly in front.

DAG'll take a look at it, eventually. I really wish I personally could as well.

 

[alex.wheatley]

I know this is an old thread but maybe someone will see it/reply?! I am having the same problems and wondering if you found any solution, because I think I have found one but am unsure whether it was the right thing to do or not. Basically after trying adjusting the mount and painting the rangefinder cam on the lens to make the lens move out to focus at infinity on the stop while also correcting the back-focus, I discovered that my front element was loose at first i tightening it the normal way (clockwise) but it came loose again, so this time i turned it anticlockwise this i noticed affected focus, so I restored the lens to its original state (in-terms of my adjustments) and found that with the front element screwed in this way the back-focus was gone and the distance scale/rangefinder/ and infinity stop were all correct. I don't know if this is of any help to anyone anymore, or wether someone can provide me with any feedback on my adjustments from any information they have gathered, seems to have fixed it but don't know if I have changed something I shouldn't have?!
Alex

 

[jdos2]

I can say that I did find a solution, but it brought its own problems.

I got rid of the M8 and associated lenses in trade for a D3 and a number of lenses.

I finally got an M9 and discovered what many have suspected all along, that almost all Leica lenses, almost all lenses at all have a focus shift- which isn't obvious on film for the combination of resolution and depth of focus at the film plane.

Then again, I never did replace the CV 40mm f/1.4- it was just too much trouble. The 35mm Lux ASPH has a focus shift, but all lenses focus accurately enough and consistently enough that I don't have issues.

This was a particularly bad lens that I had. I still doubt that the vendor ever returned it to anyone for adjustment.