Sony has just launched its newest fast aperture wide-angle prime for its full-frame Alpha lineup: the FE 20mm F1.8G lens. With two advanced aspheric and three ED elements, Sony promises outstanding corner-to-corner image quality, as well as fast autofocus thanks to XD (extreme dynamic) linear focus actuators. Have a look at our sample gallery above, and read our initial impressions about the lens below.
Spoiler alert: it’s a near perfect optic.
The FE 20mm F1.8 is sharp. Sharp and contrasty. One day we hope to have the MTF90, MTF50, and MTF20 graphs to quantitatively show you just how sharp or contrasty a lens is, but for now have a look below at the whiskers and hair on Allison’s feline (slide left to view a 100% crop):
The strand of hair at top, center, emanating from the eye is literally 2 pixels wide, yet perfectly resolved. That suggests this lens, even wide open, is capable of resolving detail for sensors far higher in resolution than the 60MP a7R IV. And the lack of any haziness to detail indicates that contrast is very high, even at this aperture and close focus distance. Animal eye AF also made this shot a breeze to capture.
(Lack of) chromatic aberrations
One of the biggest headaches when it comes to fast prime lenses is longitudinal (axial) chromatic aberration (LoCA), which rears its ugly head as purple and green fringing typically in front of, and behind, the focal plane. It’s not an aberration that you can simply click a checkbox to get rid of, and professional photographers spend hours manually cloning it out. It’s particularly a problem when it comes to wide-angle fast primes.
This lens has almost no detectable LoCA or fringing to speak of. This is pretty remarkable. Have a look above, sliding left to view feline hairs at 100%. Typically, backlit hairs will have magenta fringing and green fringing on hairs in front of, and behind, the plane of focus, respectively. But we see nothing of the sort. And the window in the background shows no color fringing around its edges, also indicating the lack of any detectable LoCA. This is truly impressive for a fast wide prime. View the full-resolution image and judge for yourself here.
Lateral chromatic aberration
If you’re worried about lateral chromatic aberration (LaCA), the one that is easy to fix in post-processing software, well, don’t be. There’s not much of it, and Raw converters automatically correct for it (also corrected in JPEG) so as to not leave any trace of it in your final output. Thankfully, lateral CA is well enough controlled that even corrected images don’t show much softening when viewed at 100% in the corners, as you can see below (slide left for the 100% view):
Distortion and vignetting
Distortion is extremely well-controlled, and can be easily remedied by leaving distortion correction enabled in the camera settings. Hover over (or click, on mobile) the ‘corrected’ and ‘uncorrected’ states below to see the extent of distortion and vignetting corrections when it comes to this lens, when shot wide open:
|Uncorrected (F1.8)||Distortion & Vignetting corrected (F1.8)|
While distortion correction does impact a large portion of the frame, the correction itself is extremely subtle, meaning that much of the distortion has itself been corrected for optically. When it comes to vignetting, a large portion of the frame displays vignetting-induced darkening at the widest aperture, but the magnitude is fairly modest. While it’s easily corrected in post-processing or in in-camera JPEGs, do note that you might have up to 1.7 EV darkening in corners of the image when you shoot wide open.
Although many of our readers won’t think much about ‘bokeh’ when it comes to such a wide optic, it’s actually very important. The entire reason for the existence of a 20mm F1.8 lens is to – aside from astrophotography and nightscape applications – isolate subjects against their backgrounds in a wide field-of-view composition. This allows a photographer to emphasize the subject against its – at least somewhat blurred – environmental background. And in such instances, the quality of the background (and foreground) blur certainly matters. Thankfully, due to improvements in grinding and polishing processes, particularly of aspheric element molds, Sony has managed to deliver pleasing bokeh. Have a look below at the rendition of out-of-focus highlights behind, and in front of, the focal plane:
There is very little onion ring patterning to out-of-focus highlights. Furthermore, there aren’t any high-brightness rings to the out-of-focus highlights, indicating that out-of-focus areas should be rendered relatively smoothly without distracting bokeh. We should note that there are slightly brighter rings to foreground vs. background out-of-focus highlights that might indicate the presence of some spherical aberration, but it’s so slight as to not be a photographically relevant consideration. Furthermore, we do see some bright-edged highlights as you approach outer edges of the frame, so we’d expect slightly busier bokeh at extremes of the frame, much like the Sony FE 35/1.8 lens.
Finally, the lack of any discernible green – and only a very slight presence of magenta – rings around out-of-focus highlights corroborates our earlier finding that longitudinal chromatic aberration is nearly nonexistent, which is an impressive achievement for a lens of this type. Nine aperture blades help to retain circular out-of-focus highlights as you stop the lens down.
Fast aperture wide-angle primes in particular are hard to produce without common optical aberrations like longitudinal chromatic aberration and a drop-off in sharpness across the frame, not to mention lateral chromatic aberration, distortion and vignetting. The Sony FE 20mm F1.8 exhibits extremely high sharpness and contrast wide open, even at close focus distances, and a lack of longitudinal chromatic aberration, seen as purple and green fringing in front of, and behind, the focus plane. Those attributes in and of themselves would have made this lens quite desirable, but the lack of lateral chromatic aberration (or, more accurately, the lack of a major decrease in sharpness after correction of any lateral CA), and only mild distortion make this a prime optic.
While there’s significant vignetting, performance is better than many other fast wide-angle primes of its type, and vignetting in general is less of a concern given modern sensors. Couple all the optical positives with class-leading autofocus speeds thank to the ‘XD’ (extreme dynamic) linear motors and you have, in our opinion, an industry-leading 20mm F1.8 lens.