Vignetting on some C-mounts as you stop down

[DanielT74]

This is my first post here, folks, and I must apologize for my ignorance and if I am spouting absolute nonsense (but I do learn!)

Anyway to cut to the chase, I have a couple of lovely C-mounts, namely Schneider Kreuznach 50/0.95 and Kern-Paillard Macro-Switar 50/1.4 which almost cover the APS-sensor wide open with only a touch of vignetting but vignette more as I stop them down.

I have heard people adapting the Schneider to Leica M8 which is a larger sensor, which got me thinking that perhaps it is the mount opening (which is of course very small in the c-mounts) that gets in the way and whether a change of mount will remove that problem.

I am currently using them on a NEX-5n but if I ever start selling pics I will upgrade to a Leica M14 or whatever it will be in 12 years!

Any insights will be appreciated, in the meantime here are some images I've shot with them recently (only had them for a short time). I hope they showcase what the lenses are capable of to some extent though I know my skill still leave much to be desired.

Schneider:

https://lh4.googleusercontent.com/-YGckCqRN50Y/T3mDZAQSeUI/AAAAAAAAS4o/hY34q-1UGTo/s800/DSC08970.JPGhttps://lh5.googleusercontent.com/-eE6FPPqh2_o/T3aDw1CfhrI/AAAAAAAASsY/fFgI_YErg_A/s800/DSC09059.JPGhttps://lh6.googleusercontent.com/-f-DavFPMNA0/T3aEe_Cg6XI/AAAAAAAAStY/8nKikRIC8IY/s800/DSC09081.JPGhttps://lh6.googleusercontent.com/-U_1zKbEy0Gc/T-CQCJstNmI/AAAAAAAAXdM/hC5rwxM77KM/s800/DSC05282_2.jpghttps://lh3.googleusercontent.com/-oGkUuMfhs-U/T8RIlk6ER9I/AAAAAAAAVsI/pM1Yq1CFTvk/s800/DSC03608-3.jpghttps://lh5.googleusercontent.com/-Xg-Rn1VpKbo/T3WodpShIvI/AAAAAAAASrg/1-wccgp5eF4/s800/DSC09003.JPG

Macro-Switar:

https://lh5.googleusercontent.com/-lgpZubGFw74/T-CGxm-uQsI/AAAAAAAAXcA/iPr2AMIfDQ8/s800/DSC06292.JPGhttps://lh5.googleusercontent.com/--b3jyJ4Elew/T-CTRNO4UfI/AAAAAAAAXdY/V3ivyqgbF4c/s800/DSC07042.jpg

[raid]

The images look great, Daniel. The second one in particular. I use a TV lens 25mm/4 which is OK when used wide open on the M4/3 format.

[JHutchins]

I don't see changing mounts helping -- the vignetting is caused by the iris itself, not the lens mount. It's just a matter of what brand of sensor you want that particular image circle falling on. They are fun lenses, though and these are some lovely photos.

[thegman]

If they just about cover APS-C, they should cover micro four thirds easily, maybe that's worth a try.

[DanielT74]

Thank you for the response, guys, for the kind word about the pics and for throwing some light on this issue.

Yes, they will definitely work on the MFT but since they vignette only very slightly basically covering the whole frame on the NEX I am mostly OK with that.

Someone over at the MF forum said that they always vignette significantly it's just that the circle of confusion becomes more and more defined as I stop down, but this doesn't seem to accord with experience as the Schneider is reasonable in the corners wide open and by f1.4 sharp whereas by f8 those corners are black. Hmmm....

[DanielT74]

One thing I just realized is that the supplied hood for the macro-switar causes vignetting on the APS-C sensor.

D'oh!