Tokina AT-X PRO FX SD 24-70 mm f/2.8 (IF) review - Coma, astigmatism and bokeh

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Tokina AT-X PRO FX SD 24-70 mm f/2.8 (IF)

8 April 2016

Arkadiusz Olech

7. Coma, astigmatism and bokeh

As long as you limit yourself to the APS-C/DX sized detector you won’t see any coma problems at all. In the corners of full frame, however, that aberration starts to be distinct and it is the easiest to notice it at the shortest focal length. A similar performance in this category we saw while testing the Tamron SP 24–70 mm f/2.8 Di VC USD but the new lenses produced by Canon and Nikon managed distinctively better in this category.

Center, 24 mm, f/2.8	Corner APS-C, 24 mm, f/2.8	Corner FF, 24 mm, f/2.8

Center, 45 mm, f/2.8	Corner APS-C, 45 mm, f/2.8	Corner FF, 45 mm, f/2.8

Center, 70 mm, f/2.8	Corner APS-C, 70 mm, f/2.8	Corner FF, 70 mm, f/2.8

The astigmatism influences the image quality in a significant way, especially at longer focal lengths. The average difference between vertical and horizontal MTF50 function values amounted to 11.7%. That result doesn’t look so bad in itself but might be misleading up to some point because it contains all focal lengths. If you look closer at particular values at 24 mm there are almost no astigmatism at all and in the 45-70 mm range, especially near the maximum relative aperture, its level is significant. If you remove the 24 mm focal length from the average the astigmatism actually increases to 17% and can be called noticeable.

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The blur provided by the Tokina 24-70 mm is pleasing to the eye for a zoom lens. Looking at out-of-focus circles of light you still can notice a trace of onion ring bokeh. That result is not huge but perceivable. What’s important, the truncation of circles connected to the mechanical vignetting is less pronounced than in the case of much more expensive rivals produced by Canon and Nikon.

Center, 70 mm, f/2.8	Corner APS-C, 70 mm, f/2.8	Corner FF, 70 mm, f/2.8

Center, 70 mm, f/4.0	Corner APS-C, 70 mm, f/4.0	Corner FF, 70 mm, f/4.0

Center, 70 mm, f/5.6	Corner APS-C, 70 mm, f/5.6	Corner FF, 70 mm, f/5.6