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Sigma FE 85mm f/1.4 DG DN Art: Hideous Pincushion Distortion and Its Effects on Micro Contrast

This page looks at the hideous pincushion distortion of the Sigma FE 85mm f/1.4 DG DN Art. The distortion is so strong that it really makes distortion correction all but mandatory.

Pincushion distortion is far more unnatural looking than barrel distortion, particularly for human faces, but it is also a Big Deal for horizons, architecture, etc. The world tends to bow-out or round-out, not pinch in as with pincushion distortion—it feels unnatural to me.

The de-facto requirement to correct this level of distortion guarantees sub-optimal micro contrast and sharpness in a substantial portion of the central areas of the frame. That makes the sharpness and Sigma FE 85/1.4 MTF chart highly misleading.

Sigma 85mm f/1.4 DG DN Art: Distortion and Distortion Correction

Sigma 85mm f/1.4 DG DN Art: Distortion Correction Impact on Micro Contrast and Sharpness

Includes discussion and uncorrected vs corrected images.

As a measure of detail, JPEG output file size is a solid indicator: the uncorrected image compresses at very high quality to 60.2MB versus 52.3MB for the corrected image. In other words, JPEG is saying that there is more than a 10% loss in pixel detail. Simply put, the Sigma FE 85mm f/1.4 DG DN Art is a very fine lens, but it is not what is cracked up to be by Sigma in terms of sharpness.

Misleading advertising

Like Nikon, Sigma engages in misleading advertising, which I deem borderline fraudulent because the very same paragraph refers to pure optical characteristics with software correction for distortion:

The angle of view for 85mm focal length helps to focus on the essential elements. In landscape and snap photography, it vividly expresses the very impression of the scene by only showing the element that appeared impressive. The edge-to-edge resolution and beautiful bokeh bring the special atmosphere that a zoom lens cannot produce. Distortion is perfectly controlled as well.

...Improving image quality and compactization were made possible by optically correcting axial color aberration which can only be corrected optically, while utilizing in-camera correction to deal with vignetting and distortion...

Below, this is a picture of my framed tulips image hanging on my wall.

f1.4 @ 1/100 sec handheld, ISO 800; 2020-09-11 08:15:38
Sony A7R IV + Sigma FE 85mm f/1.4 DG DN Art
RAW: +40 Whites, +15 Clarity, USM {15,50,0}

[low-res image for bot]
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