Nokton 50/1.5 v2 and Zeiss C-Sonnar

Some tests of focus shift.

F1.5:



F2:



F2.8:



F4:



I had to do these over 3 times, use a heavy tripod, and the self-timer to catch the shift. It is smaller than my ability to focus using a 1.25x magnifier on the M9. I shim my lenses to 0.01mm of where I want them with the M9.

There was a discussion on focus shift on another forum about this lens. It is negligible for rangefinder use, and makes me glad to not have liveview on a camera.
 
Still learning the C-Sonnar's focus shift tendencies but I'm generally pleased with how it does people shots.

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I did a bit of informal testing just now and close 0.9m (about 1-1.m). This is what I noticed, generally:

At f/1.5
No focus shift but image isn't at its sharpest; sharp enough to see details (similar to Nokton 35 1.4 wide open)

At f/2.8
There is focus shift. What is in focus is behind the intended focus point. But when adjusting for it, turning the barrel slightly clockwise, sharpness improves and is crisper than at 1.5.

Is this the usual behavior of the lens? Does this mean that my sample is calibrated for f/1.5?

Thanks!


Sent from my iPhone using Tapatalk
 
You Sonnar is most likely optimized for F1.5. The image you get is the in-focus image of F1.5 convolved with the shifted image at F2.8. What that means- the focal length of a lens is not constant across all apertures. That is due to spherical aberration.
 
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