HD Pentax-D FA* 50mm F1.4 SDM AW
Cat's Eyes
One question some advanced users may ask when looking for new fast glass is what the bokeh disks look like near the frame edges.
This is called "cat's eyes" effect (it has nothing to do with "coma", which is something which is more relevant to astrophotography) and is driven by mechanical vignetting. If you want to know more about it, please read here.
Once we found a reproducible setup to test this, we were surprised by the results simply because the actual shape of the disks seems very similar across the lenses tested.
The size of the disk is a result of the lens design combined with how we shot the images; the results are not to be compared to others' tests. The discussion that follows is limited to the outer form of the disks.
First is the result from the HD Pentax-D FA* 50mm F1.4 SDM AW:
For reference, below are results from comparable lenses:
Pentax smc FA 77mm F1.8 Limited
If you are interested in another reference you can have a look at the Zeiss Otus 55mm F1.4 cat-eye bokeh here. Larger mount diameters and short flange distances don't help, either, as can be seen for the new Canon R-mount or Nikon Z-mount. It just seems a very typical aspect of fast FF glass.
The visual result here is that the shape is very similar on all the lenses tested, with the two Sigmas having a tad more compressed cat's eye in the outer regions, but nothing really worth worrying about. We are not aware of any autofocus 50mm lens that behaves better in this regard.
Verdict: 5/5
