The Sony 20mm f/2.8 is a prime wideangle lens that offers full-frame coverage
This is a cleanly-designed lens with a super-sleek appearance. The manual-focus ring is tucked away on the flared flange at the front of the lens but can be easily located when required. This is important because the manual-focus ring rotates in AF mode so needs to be kept unobstructed when it is not being deliberately deployed.
A generous focused-distance window fills the main part of the lens barrel and is accompanied by full-frame depth-of-field markings. And that’s it: there are no switches, sliders or push-buttons. Changing between AF and MF modes is carried out using a switch on the host camera body, not on the lens itself.
A petal-type lens hood is included and can be reversed for storage. A soft drawstring pouch is also provided: this is slightly on the large side but it protects the lens from dust and knocks when it is being carried in a jacket pocket rather than a bespoke camera bag.
In use, the 20mm lens gives the equivalent of a 30mm field-of-view when fitted to an APS-C camera body (as used for this review). The AF mechanism drives the rear of the lens and works very quickly. There were some inconsistencies in the MTF figures obtained when photographing the test chart and that suggests the lens may not always have focused on exactly the same plane. However, real-world images displayed perfect focusing on all occasions.
Switching to manual-focusing disengages the AF motor and releases the manual-focus ring, which has a light touch and a generous throw that is just short of 90°. As usual, the camera’s AF sensor acts as an electronic rangefinder to confirm when perfect focus has been achieved.
MTF (Modular Transfer Function) testing generated good results (at or above the crucial 0.25 cycles-per-pixel level) from f/4 through to f/11, which ought to cover the majority of picture-taking situations. Clear colour fringing (chromatic aberration) could be seen in all of the test-chart images at the boundaries between stark black and white regions but this problem was not replicated in real-world images that lack these artificial boundaries.