Help! Back focus in Nokton 50/1.5?!

[Tveljus]

Howdy!

I tried searching the forums for info on this, but I find noone describing the kind of problem I'm having with my recently procured Voigtländer Nokton 50mm f1.5 for the Prominent cameras.

I've shot a roll with the lens on the Prominent body I got with it, and it displayed obvious back focusing on almost every shot. I thought it might be the Prominent body's fault, but now that I've shot through the lens on my Bessa R2S (the Bessa for Nikon rangefinder lenses) with the adapter for the Nokton, the same back focusing appears.

Have anyone ever experienced a classic Nokton lens back focusing?
And does anyone know if there's a way to fix the lens, or will I have to get hold of another one?

I certainly hope the latter is not the case, as I've put in a lot of effort and money in to getting the discontinued adapter and the hard to get lens... 🙁

Here's a sample picture: http://www.flickr.com/photos/tveljus/6070875725/in/photostream

 

[ampguy]

With the Bessa, you might be able to try different width adapters. How is infinity @ infinity on the bessa?

 

[Tveljus]

Different width adapters?
And if you mean how the rangefinder patch is aligned at infinity focus - it's perfect. All my other lenses also focus perfectly at infinity. If you mean how infinity works with the Nokton and the adapter, I'm not sure. It might be off actually.

 

[ampguy]

infinity setting and image quality

infinity setting and image quality

If your images at infinity (with RF and lens set at infinity) are very good, then your adapter is likely OK and you might have a lens issue.

If your images at infinity, with lens set at infinity, are off, then it might be a good thing to try a different LTM/M adapter.

The above is for use with the Bessa. I have no idea about the other mount/adapter setup you use.

Different width adapters?
And if you mean how the rangefinder patch is aligned at infinity focus - it's perfect. All my other lenses also focus perfectly at infinity. If you mean how infinity works with the Nokton and the adapter, I'm not sure. It might be off actually.

 

[Tveljus]

Ah, I see.

I use the Bessa R2S, so it's with Nikon rangefinder mount. But as the lens seems to malfunction about as much on the original camera as on my Bessa I guess it's more likely it's in the lens the problem lies.

What I want to know is: what kind of repairs or fixes are there for a back focus in the lens?

 

[ampguy]

OK, I see, I somehow thought your Bessa was an M mount camera, and the lens was an LTM.

I have no idea how those Nikon RF mount lens adapters work.

Sorry.

 

[Tveljus]

No problem, it was nice of you to try to help! : )

 

[elmer3.5]

Hi, nikon type miount has another focal length than leica type, it won´t in a test and will show shifts.

If the rnagefinder is not the problem then:

In order to know what´s going on i sugest you try once more with a ruler and focus at about 1 metre away or 3.5 feet. shoot at 1.5 and 4.
If you see consistent backfocus probably the lens needs shiming, if both shots show diverse focus , (for instance f4 nails focus but 1.5 doesn´t, or viceversa) then you have the known shifting due to difference tween broad open and stopped down (Sonnar), optimization needed.

Guess that lens is aspherical and therefore the difference tween 1.5 and 4 shouldn´t be the problem.
I think it needs reshimming.
that happened a lot to me, almost the half of the lenses i had or have needed reshimming, even right out of the factory.

Bye!

 

[Tveljus]

Hi elmer3.5!

I will try the ruler-test, thanks for the advice!

As you say though, I don't think it can be focus shift due to aperture, because I've never heard of the Prominent Nokton suffering from that.

And if it really needs "reshimming" I hope it is performable, considering the lens looks rather delicate...

Thanks again for the advice though!

 

[Tveljus]

I'd just like to report that I most likely have found the problem of the lens!

It seems that the rearmost lens element is loose, and therefore moves around when I angle and/or shake the camera lightly.

That would probably explain the very random results I got when shooting a test roll on a tripod: shots taken at the same aperture and focusing distance could display entirely different quality.

I will get my local repairmen to check the lens out, and hopefully the repair won't cost me more than 100$.

Thanks to you guys who dropped in to help! I hope this thread can be of help to anyone with similar problems in the future.