Nikon Nikkor AF-S 24-85 mm f/3.5-4.5G ED VR review - Coma, astigmatism and bokeh

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Nikon Nikkor AF-S 24-85 mm f/3.5-4.5G ED VR

27 August 2012

Arkadiusz Olech

7. Coma, astigmatism and bokeh

Attach the Nikkor 24-85 mm VR to an APS-C/DX sensor body and you won’t have any coma-related problems. The image of a diode in the corner of that type of detector is just slightly deformed so the correction of this off-axis aberration can be assessed positively.

On full frame the situation is different – the coma is visible at all focal lengths. You can observe some decreasing trend along with the increase of the focal length. At 24 mm the coma is really pronounced but at 85 mm it is reduced to a medium level.

Nikon Nikkor AF-S 24-85 mm f/3.5-4.5G ED VR - Coma, astigmatism and bokeh

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Astigmatism is hardly corrected in a perfect way as well. The average difference between horizontal and vertical MTF50 function values amounted to 11% which is a medium result. You should remember one more thing – a high level of chromatic aberration in this lens can influence the difference between horizontal and vertical resolution values. That aberration level is so significant and bothersome that it is visible already on the horizontal measurement area of resolution, positioned near the frame centre (it can be seen in the crop below: one side of the border is reddish , the other side – yellow).

The chromatic aberration doesn’t influence this vertical crop, positioned along the radius coordinate. If that aberration decreases the resolution of just one coordinate it acts like astigmatism itself and our result concerning the other aberration might be a bit overstated.

Let’s glance at defocused images of a diode which was put in different places of the frame.

The light spread in the circles is not perfectly even. On stopping down a distinct, lighter ring near the very edge of the circle becomes visible. Fortunately it is the only significant exception to the uniformity of the light spread so the bokeh, provided by this lens, should be satisfying for most of users.