Here is interesting comparison test of HD Pentax-D FA* 50/1.4 and Zeiss Milvus 50/1.4 and Sigma 50/1.4 Art. More about first two lenses.
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The test is written in russian, but can be esasily translated to english using Google translator. There are Imatest graphics of resolution as well as ISO 12233 test chart pictures.
Main notes from the author of the test:
1. The resolution of the optics (Pentax 50) exceeds the resolution of the sensor. Considering that we see the moire effect in the test chart pictures on the diaphragm 1.4, we can conclude that the lens is excellent and a higher resolution camera would not hurt it in order to realize the full potential.
2. Imatest: If the results of the ZEISS Milvus were impressive (50.1 lp/mm), then the HD PENTAX-D FA ★ 50mm F1.4 SDM AW they are generally stunning today (2018). The maximum result on the open aperture is 69.4 lp / mm!
3. Imatest CA's: The ZEISS Milvus 50 / 1.4 lens has very good blue and green channels, but in red we see a sharp drop in resolution, these are the redest “smeared” CAs, which are visible to the naked eye.
In HD PENTAX-D FA ★ 50mm F1.4 SDM AW, we see very decent red and blue channels and a very “vigorous” green channel, which has a characteristic “hump” at the top and bottom.
4. The field resolution tests showed us that the results of both lenses are visually not very different. For some moments, a very experienced eye can see that the resolution of ZEISS Milvus is slightly higher (lens tested on 50 Mpix Canon 5DSr). Tests in the studio give more accurate and controlled results. Here, visually, we were able to confirm a slight superiority in resolution with ZEISS Milvus. And an additional mathematical analysis showed that HD PENTAX-D FA ★ 50mm F1.4 SDM AW on a camera with a higher resolution could even surpass the ZEISS Milvus, 36 megapixels limit it.
5. Of the entire set of 50 mm lenses, the most similar is SIGMA DG 50MM F1.4 HSM ART. It is also a very good autofocus lens, but its optical quality is concentrated in the center of the frame and suffers at the edges, the HD PENTAX-D FA ★ 50mm F1.4 SDM AW turns out to be better at the edges.