HD Pentax-D FA* 50mm F1.4 SDM AW
Aberrations are imperfections and in the way a lens renders parts of a scene. On this page, we will take a look at both chromatic aberrations and purple fringing.
Lateral Chromatic Aberrations
Lateral Chromatic Aberrations are color errors which show up around the edges and corners of a frame. They are more pronounced the farther you get from the image center and are best seen at harsh contrast edges.
Here is an 100% crop of the corner:
You can see, there are none. The lens is perfectly corrected for LatCAs.
Longitudinal Chromatic Aberrations
These color errors grow with distance from the focal plane along the optical axis. So you do get different colors before and behind the subject. Typically the color cast are magenta and green and go away when stopping down the lens.
The HD Pentax-D FA* 50mm F1.4 SDM AW also shows some LoCA, but actually for a lens of this class it a very well controlled.
Here some 100% crop images from the torture test against the white sky:
As you can see, they are pretty much gone when stopped down to F2.8 or farther.
In this case the lens actually behaves quite well and it's easy to correct.
For comparison, the Sigma 50mm F1.4 Art
Most lenses can show additional color errors when really pushed into extreme contrast situations. Glaring glass and metal subject edges in the bright sunshine are the worst possible test. It is also a typical thing for black branches against the sky. Fringing mostly is purple, blue or reddish.
Here is a 100% crop of the worst case image part of trees against the sky when shot wide open.
Again for reference the Sigma 50mm Art:
For a direct comparison have a look at a number of shots from fast lenses, beginning with the HD Pentax-D FA* 50mm F1.4 SDM AW:
While it is at least on par in this discipline with its direct competition like the Sigma 50mm Art and certainly significantly better than the Sigma 85mm F1.4 EX DG HSM or SMC Pentax-FA 77mm F1.8 Limited (see above), it is not perfect here. But, for a F1.4 lens of this type, it still does pretty well.
Comatic Aberrations and Astigmatism
Not for normal daylight use relevant, but maybe someone wants to know for night sky photography: Comatic aberrations and astigmatism.
Ideally point light sources like stars should stay points even on the edges and in the image corners.
Please consider both the following images are enlarged to more than 200%. The first one is from the lower left corner.
So the HD PENTAX-D FA* 50mm F1.4 SDM AW doesn't show any relevant coma or tangential astigmatism and shows only mild sagittal astigmatism in the extreme corner when shot wide open.
Stopping down the lenses reduces / removes this type of aberration.
For reference here the Sigma 50 Art, which on the right side image edge shows both mild sagittal astigmatism (the wings of the "bird") and mild coma (the tail of the "bird"):