Tamron 20mm F/2.8 Di III OSD M1:2 Review
The Tamron 20mm F/2.8 Di III OSD M1:2 is a fairly fast, ultra-wide-angle prime lens for Sony's extensive range of full-frame and APS-C sensor mirrorless cameras.
It features a maximum aperture of f/2.8, an Optimized Silent Drive focus motor for quiet AF operation, and a moisture-proof construction.
The optical formula comprises 10 elements in 9 groups, including one moulded glass aspherical element and three low-dispersion elements.
It has an iris diaphragm with seven rounded aperture blades.
This lens is ideal for close-up shooting, offering a minimum focus distance of 0.11m and a maximum reproduction ratio of 1:5.
The Tamron 20mm F/2.8 Di III OSD M1:2 lens is priced at £399 / $349.
Ease of Use
The Tamron 20mm F/2.8 Di III OSD M1:2 is a compact, lightweight wide-angle prime lens, measuring just under 6.5cms in length and weighing in at 220g.
You can also use it on a smaller Sony APS-C body, where the effective focal length changes to 30mm due to the 1.5x crop factor.
Build quality is very good, despite the all-plastic construction and the attractively low price-tag. The Tamron 20mm F/2.8 Di III OSD M1:2 feels solid enough in your hand, and it has a metal mount.
Note that the bayonet fit is very firm, so much so that it requires quite a strong twist to mount/unmount the lens. Whether or not it will loosen up with prolonged use remains to be seen.
The focusing ring is generously wide given the overall size of the the lens and it has a ridged, rubberised grip band.
There are very few features though - no distance scale, no depth of field scale, not even an An AF/MF switch on the side of the lens to make it easier to switch between the two focusing systems.
The lens also doesn't offer built-in Vibration Compensation, instead relying on the Sony camera body to provide image stabilisation (if indeed it supports it).
The Tamron 20mm F/2.8 Di III OSD M1:2 features an OSD (Optimized Silent Drive) motor that claims to allow near silent auto-focusing. Importantly, this solution also allows full-time manual focus override, even when the focus mode is set to AF.
In use, we found the auto-focusing to be fairly sluggish - and certainly nowhere near instantaneous - with the lens mounted on a Sony Alpha A7 III camera. It's also pretty audible, despite Tamron's assertion that its silent, making this lens less well-suited for video use.
The lens is supplied with lens caps and a removable slim, petal-shaped lens hood - there's no bag included. Filter size is 67mm.
The Tamron 20mm F/2.8 Di III OSD M1:2 offers an angle of view of 94°30'.
Chromatic aberrations, typically seen as purple or blue fringes along contrasty edges, are not really a problem with this lens.
Vignetting and Distortion
With the Tamron 20mm F/2.8 Di III OSD M1:2 wide open at f/2.8, you can see some very noticeable light fall-off in the corners. Stopping down helps, although to completely get rid of this phenomenon, you will need to use an f-stop of f/8 or smaller.
There's also some very obvious barrel distortion apparent which you'll need to correct in post-processing or avoid by turning on the in-camera correction.
With a maximum reproduction ratio of 1:2 and the ability to focus very closely at 11cm from the film/sensor plane, the Tamron 20mm F/2.8 Di III OSD M1:2 doubles up as a very useful macro lens. The following example illustrates just how close you can get to your subject.
The Tamron 20mm F/2.8 Di III OSD M1:2 produces nice sunstars when stopped-down to f/16 and f/22, although unwanted flare effects are apparent when shooting directly into the sun, even with the lens hood fitted.
Bokeh is a word used for the out-of-focus areas of a photograph, and is usually described in qualitative terms, such as smooth / creamy / harsh etc.
Isolating the subject from the background is normally hard to do with an ultra-wide-angle lens such as the Tamron 20mm F/2.8 Di III OSD M1:2.
Tamron have employed an iris diaphragm with 7 rounded blades, which coupled with the ability to get really close to your subject makes for a fairly pleasing rendering of the out-of-focus highlights when shooting wide open at f/2.8.
Below you'll find some examples, but you are also encouraged to check out our full-size sample images.
In order to show you how sharp this lens is, we are providing 100% crops on the following page.