Leica APO-Summicron-SL 75 mm f/2 ASPH. review - Coma, astigmatism and bokeh

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Leica APO-Summicron-SL 75 mm f/2 ASPH.

18 August 2025

Maciej Latałło

7. Coma, astigmatism and bokeh

Dealing with a lens with such parameters and price we didn't expect any problems with coma correction and indeed there are no problems – as long as you stay within the APS-C sensor area. When you look into the very corner of full frame, the point-like image of a diode turns into a slight triangle. Deformations are very slight here so, even if they are perceptible, they don't provide you any serious reasons to complain.

Center, f/2.0	Corner APS-C, f/2.0	Corner FF, f/2.0

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

In order to make the performance in this category comprehensive, we decided to present crops of photos of the sky taken from the right-hand upper corner of full frame. This time these are shots taken by f/2.0, f/2.8, and f/4.0. It is clear that even on stopping down the aperture by 2 EV coma is not corrected completely and effects of its influence remain visible in a shape of a small 'comma'.

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Corner FF, f/2.0	Corner FF, f/2.8	Corner FF, f/4.0

Astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounted to just 3.7%. It is a result we consider to be very low so the tested lens deserves to be praised.

The appearance of out-of-focus images produced by the tested Leica is untypical. I expected here perfect circles with a very even light spread, of course not excluding a delicate onion-ring bokeh effect because this construction does feature one aspherical element. There's no onion-ring bokeh but you see a bandlike structure instead, an effect I haven't seen in any telephoto lens with good aperture fastness before. As a kind of consolation you can add that the light rim is not especially accented. Mechanical vignetting gives you a lot of reasons to complain for a change. The lens is big and heavy and yet this effect remains perfectly visible and it doesn't disappear even on stopping down the aperture by 2 EV. If the lens was wider, not only long, the circles wouldn't be so truncated in frame corners.

Center, f/2.0	Corner APS-C, f/2.0	Corner FF, f/2.0

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

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