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Reader Question: Considering Focus Breathing Performance for Focus Stacking When Choosing a Lens

Glenn K writes:

You frequently comment on the way in which distortion correction (moving and stretching pixels) destroys fine detail and micro contrast.

But what about stacking software. In order to deal with focus breathing, Zerene Stacker must be scaling images in a stack, presumably without any sharpening. I don't know whether it selects the smallest of the stack and scales the other images down, the largest and scales the other images up, or some combination. Couldn't find this discussed in the Zerene Stacker (or Helicon) documentation. If this is what is being done, doesn't it now make focus breathing a more important aspect of choosing a lens than the last ounce of micro-contrast?

As an example, consider your comparison review of the Zeiss Loxia 35mm f/2 and the Nikon Nikkor Z 35mm f/1.8 S. The Loxia edged out the Nikkor on fine detail, micro-contrast, field flatness and lack of distortion. But given low focus breathing, low CA and focus stacking ("shift") of the Z7, does this mean one might make better overall images with the "loser" of the sharpness comparison?

DIGLLOYD: first, distortion correction degrades (not destroys) micro contrast though for lenses with barrel distortion, it can actually improve micro contrast in central areas (pixels compressed together) and degrade it in outer zones (pixels stretched apart). For pincushion distortion, it’s much worse—pixels are stretched apart in much of the central areas of the frame, which is generally the most important area. That is why MTF charts are not truthful for lenses that flag distortion correction as required—Zeiss is guilty of this and other vendors too.

Focus breathing is a worthwhile consideration for choosing a lens. It is never desirable for the photographer, and definitely a downside for focus stacking, as quite a lot of stretching must occur to match near images to far ones.

Zerene Stacker: key the focus stack of near or far frame

Zerene Stacker has awesome support and is very well thought out in many ways; it is what I use exclusively at this point. One of its many great features is the ability to reverse the order of the stack so that the first frame can be the near shot or the far shot, which means the other frames are stretched or shrunk to match, which is critical in some situations—I don’t want the summit of a peak chopped off!

Going forward, focus breathing will bubble up to considerations I test for. I forgot to look into this to compare to Zeiss Loxia 21mm f/2.8 to the Voigtlander FE Nokton 21mm f/1.4 ... I will rectify that soon when the Sony A7R IV arrives.


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