Sony FE 20mm F/1.8G Review

The Sony FE 20mm F/1.8G is an ultra-wide-angle lens with a bright maximum aperture for Sony Full-Frame Mirrorless Digital Cameras. This high-end G-series optics is the widest prime lens Sony makes and the only bright ultra-wide prime on the market with a weatherproof construction. Even with its high-grade construction, the FE 20mm F/1.8G is the lightest lens in its class.

As one of the newest E-mount lenses, the Sony FE 20mm F/1.8G incorporates numerous features. A rarity shared only by a handful of Sony lenses is a dedicated fly-by-wire aperture-ring. The aperture is continuously variable with optional clicks on 1/3-stops. This lens offers a customizable button and focus control-switch typical of Sony lenses.

This exceptionally light and compact ultra-wide-angle lens captures 94° field-of-view with a bright F/1.8 maximum aperture. Its angle-of-view is particularly well-suited for capturing huge architecture and dramatic landscape. With the added bonus of a truly bright aperture, this extends to dimly light buildings, interiors, moonlit landscapes and astrophotography. The optical design of a prime lens allows the FE 20mm F/1.8G to render better bright spots and light points common in nightscapes than a zoom lens.

The Sony FE 20mm F/1.8 offers a minimum focus-distance of 19cm which translates into a 0.2X magnification. Another significant advantage for night photography over most ultra-wide zoom lenses is that the FE 20mm F/1.8G has a nearly flat front that can accommodate 67mm screw-on filters. An removable petal-type lens hood is included with the lens to minimize flare.

Construction

There is a uniformity to most recent Sony FE lenses, including the 20mm F/1.8G. Its barrel is make of a single tube of high-grade plastic. This largely cylindrical lens narrows slightly to the width of the lens mount for about 1cm. Most of its body is 7cm wide with the a slightly wider 74mm edge to make the filter-thread sufficiently wide to avoid blocking the field-of-view.

At only 373g, the FE 20mm F/1.8 is the lightest bright ultra-wide prime with Full-Frame coverage and measures a compact 85mm long. This makes the lens feel quite dense and very sturdy. Professional grade weather-sealing is present at the mount and inside the barrel to withstand the elements.

Near the front of the lens barrel there is a 2cm-wide fly-by-wire focus-ring. Since this is a fly-by-wire ring, the camera is free to decide when to react. A switch near the base of the lens barrel selects between AF and MF mode. Sony cameras currently allow manual-focus when the switch is set to MF or when the camera is set to DMF and only right after autofocus is achieved. This means that when the camera is unable to focus, the switch must be set to MF to allow manual focusing.

A round customizable button is found right above the AF/MF switch. Similarly to most other G and GM series lenses, the function of this button is assigned by the camera to which it is mounted. Right above this function button, a silver G badge indicates this is a high-end lens. Diametrically opposite of the badge is a vertical slider that switch the aperture-ring from click to declick mode. Regardless of its state, there is a strong detent at the A position of the aperture-ring.

A fly-by-wire aperture-ring like this one is uncommon yet allows aperture-control to be switched between the camera and lens. The ring itself is about 1cm wide with half covered by hard plastic ribs to provide purchase. The detent at the A position is very stiff but those between each 1/3-stop are quite soft. It is pretty much impossible to switch between A and F/22 without shaking the lens. Similarly to the focus-ring, selecting an aperture via the aperture-ring is only possible when the camera expects it which is the case in A and M exposure-modes exclusively. One cannot use the ring to perform Program-Shift.

Sony FE 20mm F/1.8G Sharpness

Ultra-wide lenses are challenging to design optically and so they frequently show more optical defects than other lens types. Their expansive field-of-view makes it extremely difficult to render details consistently across the entire imaging circle. Sharpness is critical for lens performance.

Optically, the Sony FE 20mm F/1.8G is truly impressive. This lens renders the central portion of images with absolute peak sharpness even wide open at F/1.8. Stopping down maintains this incredible level of details until the diffraction limit around F/13 when mounted on the Sony Alpha A7R IV
Sony Alpha A7R IV.

Corners are visibly soft at F/1.8 which is completely expected. F/2 obviously is nearly identical but sharpness gradually improves by stopping down from there. By F/4, corners are much less soft and appear reasonably sharp in medium-size prints. Narrower apertures produce sharper results with peak corner sharpness at F/8.

Shown below are 5 crops taken from a photograph, repeatedly captured for each combination of focal-length and aperture. Smaller pieces are cropped from extreme corners of the images, while the middle wide crop is taken from the center of images. Select an aperture in a row for a desired focal-length to see the crops from the corresponding image. When judging image quality, understand that these are crops from a 61 MP image which is normally used to print images up to 45x30". On a computer display, these may appear much larger which magnifies image defects.

Performance

Optically this lens delivers a nearly impecable performance. Distortion, which is often significant when it comes to wide-angle lenses, is virtually zero. Measurements show straight lines deviating under ½% deviation across the frame. This performance makes distortion invisible in images. Most recent Sony mirrorless digital cameras can apply distortion correction in-camera yet this is not recommended as the process damages image-quality and also impact frame, which is to a lesser extend relevant with mirrorless cameras but unwanted elements may show up in RAW files that do not have distortion compensation applied.

The single area that Sony consistently sacrifices in their lenses is vignetting. It is a sensible choice when making a compromise since software correction of vignetting is effective and has minimal impact on image-quality. Indeed, the FE 20mm F/1.8G shows some substantial vingetting when left uncorrected. There is 3 EV of corner-shading wide-open. Stopping down to F/2.8 improves results by a full stop. Closing the aperture further down though has little impact on vignetting, so expect over 1½ EV of darkening on all uncorrected images.

With Vignetting Compensation enabled on the Sony Alpha A7R IV, noticeable vignetting remains at wide apertures, over a full-stop from F/1.8 to F/2.4. That quickly clears up by closing down the aperture. F/2.8 leaves ¾ EVs which is noticeable, particularly against the sky. F/4 lowers it to ½ EVs which is certainly more subtle. Most image processing software such as Adobe Lightroom Classic can completely remove this level of vignetting.

The Sony FE 20mm F/1.8G focuses light very precisely across wave-lengths which produces very sharp edges without any purple-fringing. Even along edges of extreme contrast, chromatic aberrations are very rare. Plus, the few that may appear can be automatically corrected by in-camera image processing. Sony Nano AR coatings on lens elements very effectively supress flare..

Autofocus powered by dual linear motors allow this lens to focus rapidly. It locks focus in under 1/4s in good to moderately low-light, slowing down slightly as level levels drop. This is not quite as fast as the FE 35mm F/1.8 reviewed in the next page yet sufficient for most uses. Note that Sony camera autofocus at the chosen aperture by default which diminishes the amount of light reaching the sensor. With a completely internal focusing system, autofocus of the FE 20mm F/1.8G is completely silent.

Conclusion

The widest Sony prime lens for Full-Frame E-mount mirrorless digital cameras is absolutely worth its price. This G-series lens delivers an excellent performance on all fronts in a relatively compact and surprisingly light weatherproof body. Even though there are other bright ultra-wide primes from third-party manufacturers, none is weather sealed and all are heavier.

Optically, the Sony FE 20mm F/1.8G renders details with perfect sharpness even wide-open in the center of the frame. Extreme corners show definite softness at bright apertures but improve steadily, reaching peak sharpness at F/8 which is a very common aperture to capture ideal subjects for an ultra-wide lens. Its bright maximum aperture allows for a moderately shallow depth-of-field where corner sharpness is not crucial.

Distortion is absent from the FE 20mm F/1.8. This lens is highly resistant to chromatic aberrations and flare too. Its only performance issue is unusually high vignetting which thankfully becomes manageable by stopping down and is completely correctable via software without detriment to image-quality. This is a logical compromise to make this lens so light. The autofocus mechanism of this lens is impressive with its fast speed and ultra-quiet performance.