CV21mm problems?

[AgentX]

Hi-

Just unwrapped a new CV21mm in screw mount and used it on my M with a CV28-90mm LTM adapter.

Finder's great and the lens seemed to be really high-quality. However, it focuses pretty far past infinity on the rangefinder. (no such problem with other lenses...) Didn't notice any out-of-focus issues on the roll of film I shot, but I was wondering if this was normal or my lens had a problem. I'm guessing the DoF covers most focusing errors except perhaps the closest-and-widest-open shooting you could do with this lens.

Also, it seems that some of the images, especially those of large, high-key scenes, are darker (in the positive) on the left side than they are on the right. I was expecting some vignetting, but this doesn't seem very even.

Anyone else had similar issues?

 

[notturtle]

this lens can have issues. sounds like you need to shoot some more under controlled conditions to see if there is an issue or not

 

[Mablo]

I have a LTM CV 21mm. It doesn't - and it shouldn't - focus past infinity. It doesn't vignette eather and my negs are always even as they should be. Something is not right on your lens I'm afraid.

 

[AgentX]

Hm. The overfocus is definitely there, although not as bad as I originally thought. If that's the only problem I probably won't bother returning it, as it's pretty slight.

What I thought was darkening on the left side in some pics only seems to be, in some others, fairly even light falloff towards the edges. Attached find a scan showing this, both original and with Lightroom vignette compensation (+23) applied. (Yeah, it's not a great shot and it's not spotted, but shows the issue, or lack thereof.)

What say you? Suddenly I think there's not such a big deal.

 

[notturtle]

differences can be down to where the sun is. Much more noticeable effect in very wide lenses...

 

[Larry Manuel]

>differences can be down to where the sun is. Much more noticeable effect in very wide lenses...

Very good point. The sky polarizes the sunlight.

 

[AgentX]

Thanks all for the input--the sun was low in the sky and that seems to account for the changes in brightness. I'll use it some more before taking any kind of action...

 

[akalai]

Just something else to consider...

I found that critical focusing was dependant on what LTM -> M mount adapter is used, especially with wide angle lenses.

I started using my Avenon 21mm (Mk.III) on a Bessa T with a Leitz 50mm LTM adapter but found it was front focusing. The easiest solution to the problem was finding and using an original later version of the Leitz 21 - 35mm LTM -> M adapter with the cutout section at the bottom of the mount.

The problem lies not only in the thickness of the LTM adapter, especially critical for wide angle lenses, but also how the lens sits once mounted.

There is a better description with some images showing the variation of how a lens can sit with different adapaters here;

http://www.rangefinderforum.com/forums/showthread.php?t=5732

If you have another LTM->M adpater, especially an older Leitz one, handy just try remounting your lens on it and see if you get a different lens position and focus. Worth a shot!

Good luck!