Sony FE 20-70mm F/4G Review

The Sony FE 20-70mm F/4G is now the most versatile FE lens on the market. Its extremely wide field-of-view is well-suited for photographing architecture, sweeping vistas, monuments and interior photos in tight places. The middle of its range is excellent for casual photography of daily life, environmental or group portraits and events. The narrow end can capture good portraits and closeups, more so due to its high 0.39X maximum magnification. Its field-of-view works really well for street photography and can even handle astrophotography.

With a constant maximum aperture of F/4 across the zoom range, this lens captures a decent amount of light at any focal-length. This is certainly not considered bright yet very few zoom lenses have more than a stop of advantage. Modern mirrorless digital cameras have extremely effective image-stabilization systems, much better than any lens-based mechanism, which allows this lens to be easily used in low-light for relatively still subjects.

Wide lenses nearly always capture an expansive depth-of-field. Using the FE 20-70mm F/4G, it is possible to isolate a subject from the background by shooting at a close distance towards the long end of the zoom. A 9-blade iris makes bokeh look smooth. The front of the lens is equipped with a 72mm thread to accept standard screw-in filters and a bayonet to attach the included lens hood.

Construction

Sony built the FE 20-70mm F/4G from sturdy high-grade plastic. Its barrel is mostly cylindrical with a diameter of 8cm. Near the back, a 45° angle slant leads to a narrower 6cm segment which lines up to the width of the Sony E-mount. The 10cm length of this lens make it feel very dense and solid. Although it is slightly heavier than the Version-Tessar T* 24-70mm F/4 ZA OSS, it is lighter than the FE 24-105mm F/4G OSS by over 35%!

An inner barrel extends 4½cm when the lens is zoomed to 70mm. It fits the outer barrel with a tight tolerance and remains completely steady. There is no zoom creep when carrying this lens. Focusing is completely internal and does not affect the length of the barrel, nor does it cause the front element to rotate. In Autofocus mode, turning the focus-ring has no effect.

A 1½cm space separates the focus-ring from a wider zoom ring. This ring operates smoothly with a moderate amount of resistance and takes the lens from one extreme of the focal-range to the other with a 90° rotation. Markings for standard focal-lengths turn with the ring. A slim gap separates the Zoom Ring from the aperture-ring. The aperture-ring has an automatic detent plus one for every third-stop from F/4 to F/22. Detents give a moderate amount of resistance and is more pronounced between A and F/22. A small lock at the base of the aperture-ring locks it in Automatic position. Note that this A position signifies the aperture is under control of the camera, it will only be automatically set when the camera is set to Auto, Program or Shutter-Priority mode. On the opposite side of the lens barrel, another switch toggle aperture detents.

Back to the space separating the Focus-Ring from the Zoom-Ring. This section holds a standard AF/MF sliding switch, plus two custom buttons configured by the camera. Only one feature gets assigned to these buttons. There are two to make it easy to access in both landscape and portrait orientation. Both buttons have the same nice springy feel. This lens offers every essential feature of a premium lens.

The front of the FE 20-70mm F/4G features a bayonet mount to attach the included petal-type lens hood and is threaded to accept standard 72mm filters. The external zoom mechanism carries along the hood. The majority of zoom lenses operate this way. The hood itself is made of rigid plastic, similar to the lens barrel.

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Sony FE 20-70mm F/4G Sharpness

Optics for zoom lenses are challenging to design, particularly considering that extremely-wide lenses typically use completely different optical formulas from normal ones. Sony engineers had to come up with a set of optical elements that can handle both extremes while remaining sharp throughout a 20-70mm zoom range.

Central sharpness of the Sony FE 20-70mm F/4G is exemplary. Fine details are captured with great accuracy in the central portion of images. From wide-angle to the long end, images are sharp even wide-open. At its widest focal-length, the FE 20-70mm F/4G shows maximum sharpness from F/4 which is extremely impressive From the middle of the zoom range onward, the center stays sharp wide open with just a hint of softness that goes away stopped-down by a ½-stop to F/4.5.

Sharpness is completely consistent from F/4.5 to F/11. When mounted on a 61 Megapixels Sony Alpha A7R V, diffraction hits at F/13, causing generalized softness. Nothing can be done about this since diffraction is caused by physical properties of light.

Image corners are rarely as sharp as the center on most lenses, yet the Sony FE 20-70mm F/4G manages an exceptional performance. Extreme corners show visible softness wide-open at wide-angle. Stopping down very gradually increases sharpness from F/4 to F/9.5. Large prints show sharp corners at F/5.6 but poster-size photos require F/6.7 or F/8 to look completely sharp.

The middle of the zoom range follows shows similar sharpness. Extreme corners look soft at F/4 They become really sharp at F/5.6 and improve even further all the way to F/8. The widest stop should be avoided when making poster-sized prints. At 70mm, observed sharpness exhibits the same properties. This time, F/5.6 is sharp enough for enormous prints, F/6.7 is better and F/8 is razor-sharp.

Upper Left

Upper Right

Center

Lower Left

Lower Right

Performance

Geometry is captured perfectly by the Sony FE 20-70mm F/4G. Lines are rendered completely straight and there is no measurable distortion at any combination of focal-length and aperture. This is too-good-to-be-true and Sony may be forcing hidden distortion correction. On a Alpha A7R IV
Sony Alpha A7R IV, there is no control over distortion correction when this lens is mounted. While this can reduce critical sharpness, on a mirrorless at least it does not affect framing, as it would on a DSLR.

Chromatic aberrations are absent from images captured by the FE 20-70mm F/4G. In cases where edge contrast is absolutely extreme, some slight color-fringing may appear, yet it is absolutely minimal. Color and contrast are rendered remarkably well by this lens. Sony lens coatings show excellent quality and, in this case, cameras do not force automatic software removal of chromatic aberrations.

The Sony FE 20-70mm F/4G manages flare extremely well. Even when a bright light source appears within the frame, there flares rarely appear and overall contrast is maintained. The included lens hood provides some protection at wider focal-lengths. Bokeh is rendered really smoothly by the 9-blade aperture in this zoom lens.

Vignetting is clearly an issue for this lens. There is a severe brightness falloff towards corners which the camera is unable to correct at this time. This result in corners that appear a full-stop darker than the center of images. It is easy to correct for vignetting using software with minimal impact to image-quality, so a future firmware could produce better results. Currently, most optic-aware image-processing software can remove this vignetting.

Similarly to the majority of wide lenses, stopping down the aperture improves vignetting. While we see over a stop of shading at F/4, closing down the aperture to F/5.6 brings it to a reasonable 1/3-stop. Another stop further down virtually does away with vignetting. Towards the second-half of the zoom, vignetting is definitively less pronounced yet still requires at least F/5.6 for it not to be easily noticeable.

Autofocus performance is impeccable. This lens focuses on any subject nearly instantly, even when contrast is low. When light levels drop, the lens naturally takes a little longer to focus yet it locks focus accurately with great consistency. The internal focus motor, which only moves internal elements to focus, of the FE 20-70mm F/4G is completely silent. There are very few moments of focus hesitation. Minimal back-and-forth movements are only noticeable at close focusing distances in moderately low light.

Autofocus is virtually silent thanks to the internal structure of the focus drive. Even manual focus is completely quiet since it is driven by the same mechanism. The fly-by-wire focus-ring is extremely responsive and feels continuous throughout the focusing-range. Custom lens buttons respond quickly too.