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Archive 2017 · Contax 35-70mm decentered?

  
 
perselio
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p.1 #1 · p.1 #1 · Contax 35-70mm decentered?


I recently bought a used Contax C/Y 35-70mm f/3.4 in Exc+ condition for my Sony A7II but upon testing it both at infinity and on a flat target at close range it turned out to be misaligned throughout the whole focal range. The right side of the image is softer than the left, with the upper right quadrant being especially problematic. Also, the upper section of the image is significantly darker than the lower section, almost as if there was an ND grad on the lens. The test was done in both landscape and portrait orientation, with the camera held first normally and then upside down (so 4 frames in total), at f/3.4 and f/5.6.

As an example, below is a 100% crop of the lower left of the image. When the camera is inverted, the portion of the lens that would normally be upper right is now depicting the lower left. You can see that in the second crop the image is both softer and darker.

I tried two different adapters (Fotodiox Pro and Novoflex) and got identical results. One thing I noticed was that with both adapters infinity is reached way before the hard stop. (I don’t have any other C/Y lenses to compare).

Would you return this lens for a refund? Or is this something that can be fixed for a reasonable fee?

Contax 35-70mm f/3.4 decentering test

For a larger image click
here



Apr 27, 2017 at 04:57 PM
jcolwell
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p.1 #2 · p.1 #2 · Contax 35-70mm decentered?


Long story short, I'd return it.

I've used many adapted Contax lenses on Canon EOS cameras, and infinity focus has been accurate at the focus ring hard stop, with decent adapters. OTOH, I've had the infinity stop adjusted on four or five Pentax and Mamiya 645 lenses, not to mention Samyang/Rokinon.

Asymmetric sharpness is often a sign of adapter problems, but Fotodiox Pro should be OK (I have many) and Novoflex is about as good as it gets. I prefer using Leitax mounts when available (including on a CZ 35-70/3.4), but Novoflex has a sterling reputation for making precision adapters (which are also very expensive).

In your sample images, the lower left foreground is certainly less sharp, but the details on the more-distant roof of the building seem sharper in the lower left image (compare short horizontal structures on either side of what appears to be solar panels). Something's not right.



Apr 27, 2017 at 05:23 PM
perselio
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p.1 #3 · p.1 #3 · Contax 35-70mm decentered?


jcolwell wrote:
In your sample images, the lower left foreground is certainly less sharp, but the details on the more-distant roof of the building seem sharper in the lower left image (compare short horizontal structures on either side of what appears to be solar panels). Something's not right.


You're right, that's quite odd. With the camera held normally, foreground sharpness in the lower left corner is ok but the mid-field is blurred. Conversely, with the camera inverted, the left corner is blurred but the mid-field improves.

So I guess it will have to go back, which is a shame as the mechanics are perfectly smooth and the optics are nice and clear.



Apr 28, 2017 at 03:00 AM





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