LensTip.com

Lens review

Sony FE 14 mm f/1.8 GM

20 April 2021
Maciej Latałło

7. Coma, astigmatism and bokeh

The coma aspect is quite interesting. During the online press conference that took place right before the official launch of the Sony FE 14 mm f/1.8 GM we were informed that landscape astrophotography would be one of the main application of the new lens. Its optics was supposed to be optimized when it comes to coma correction and, generally, the correction of higher degree off-axis aberrations that deform point-like images of stars. We were shown appropriate comparisons between the Sony and its direct rivals and it seemed the new Sony lens would simply outclass them hands down in this area.

I don't know what lens was used to take the photos presented during that Sony press conference but I am sure I got a completely different specimen for testing. First symptoms of classic coma are visible already on the edge of the APS-C sensor - by f/1.8 and also by f/2.5, point-like images of the diode change into small commas. In the corners of full frame apart from coma you see wings and it means a higher degree aberration makes itself felt (it can be e.g. a component of sagittal plane diagonal spherical aberration).

As you see, something that was announced as a strong point of the Sony in reality proved to be its slip-up.


Please Support Us

The coronavirus crisis has been adversely affecting many businesses and, sad but true, ours is not an exception. Despite that difficult situation we would like to preserve continuity and high quality of publications available on all our websites. Still, we are now aware it might be impossible without additional financial help. That's why we would like to ask all those who visit, read, and care about Optyczne.pl, LensTip.com i Allbinos.com for support - it's enough you send us a small sum of money via PayPal. If a lot people decide to support our websites we think we'll stand a chance and survive next months without any lasting harm. We count on your support and understanding, stay safe and be healthy.

- - - - - - - - - - - - - - - - - advertisement - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Center, f/1.8 Corner APS-C, f/1.8 Corner FF, f/1.8
Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh
Center, f/2.5 Corner APS-C, f/2.5 Corner FF, f/2.5
Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh


Astigmatism, understood as an average difference between horizontal and vertical MTF50 function values, amounted to as much as 25.7%. It is, unfortunately, a high value. Combination of that aberration and significant depth of field, provided by this lens, produces very interesting effects which we are going to mention also in the autofocus chapter. Here we would like to add only that astigmatism, as every off-axis aberration, increases as you go further from the frame centre and really interesting things might happen on its very edge. Even if you set the focus in the centre in such a way so you can minimize differences between horizontal and vertical MTF50 function values, these differences might reach as much as 100% on the very edge. You might observe more interesting performance when you set the focus in such a way that image quality in the centre (as a median of horizontal and vertical values) is at its highest; in such a situation huge differences stemming from the presence of astigmatism can be observed. Even if the overall image quality and sharpness in the frame centre is very good, its horizontal and vertical components on the very edge (depending on the setting of the autofocus) can feature significant blur.

Perhaps in the case of a 14 mm lens out-of-focus areas are not exactly a feature you pay the most attention to but still, they are worth a closer look because, once again, you can notice several interesting things. First, circles of light in the corners are deformed mainly because of mapping of such a wide angle of view on the flat surface of the detector but not because of mechanical vignetting. Second, aspherical elements, used in the optical construction of the lens, make themselves felt as onion-ring bokeh. Third, you can notice a brighter rim in circles we got in the frame centre without any problems. All these effects were present also in the test of the Sigma A 1.8/14 but to a lower degree; in this category the rival lens undoubtedly prevails.

Center, f/1.8 Corner APS-C, f/1.8 Corner FF, f/1.8
Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh
Center, f/2.5 Corner APS-C, f/2.5 Corner FF, f/2.5
Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh
Center, f/3.5 Corner APS-C, f/3.5 Corner FF, f/3.5
Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh Sony FE 14 mm f/1.8 GM - Coma, astigmatism and bokeh