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Zeiss Batis 85mm f/1.8 Sonnar: MTF Series from f/1.8 - f/16 + Distortion

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Zeiss Batis 85mm f/1.8 Sonnar

The Batis line is a new lens line for Sony mirrorless cameras (Sony A7 series). See the general discussion of the Zeiss Batis lenses.

I expect to have the Zeiss Batis 25/2 Distagon and Zeiss Batis 85/1.8 Sonnar in for extensive field testing sometime in June. Coverage will go into Guide to Mirrorless.

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MTF

The MTF chart shows excellent micro contrast wide open at f/1.8 with highly uniform sharpness corner to corner at all apertures. Overall contrast is superb wide open, even into the corners.

Peak performance is reached at center by f/2.8, but the variation (wave inflection) across the field looks to be a mild field curvature; stopping down a bit more delivers outstanding micro contrast at f/5.6, far exceeding most lenses and no less good than the very best Leica M lens. Minor astigmatism is present.

Diffraction drops contrast overall and for fine detail at f/8 (in effect what one hopes to see, indicating an excellent performer). By f/11 its effects are quite dulling. At f/16, the performance becomes much inferior to f/16. See Mitigating Micro Contrast Losses from Diffraction Blur in MSI. These behaviors are all expected and good in this sense: a lens that shows little effect from diffraction is not very good to begin with! In other words, the better the lens, the more diffraction throws a wet blanket onto performance.

 
MTF for Zeiss Batis 85mm f/1.8 Sonnar from f/1.8 through f/16
Graphs courtesy of Carl Zeiss

Distortion

Some pincushion distortion is typical for medium telephoto lenses, buy this level of distortion when uncorrected will be very noticeable. By comparison, the Zeiss 85mm f/1.4 APO-Planar has distortion so close to zero it can be called distortion-free, and the Zeiss 85mm f/1.4 Planar has about 0.2% distortion—about 15X less than the Batis 85/1.8. All lens designs are compromises, so it seems that distortion was traded off for uniformly high sharpness and a smaller/lighter design, knowing that the camera can correct for it automatically (or the raw converter).

To my eye, pincushion distortion is visually troublesome compared to barrel distortion, and this 3% pincushion distortion is unacceptable for many purposes if not corrected: skylines, buildings, etc would bow upwards, and filling the frame with a face is not going to look flattering—so plan on enabling distortion correction for the 85/1.8 Sonnar.

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Distortion for Zeiss Batis 85mm f/1.8 Sonnar
Graphs courtesy of Carl Zeiss

Vignetting

Vignetting to the extreme corner area is 2+ stops at f/1.8 without correction, and about 1.25 stops with correction. I’m generally not a fan of vignetting corrections, since vignetting is also a creative tool. It is potentially worrisome for gradient transitions, but if the camera does the correction in 14-bits internally (before the Sony 11+7 lossy compression file is saved), then it should nearly always be just fine.

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Vignetting for Zeiss Batis 85mm f/1.8 Sonnar
Graphs courtesy of Carl Zeiss
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