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Tamron 20mm f/2.8 Di III OSD M1:2 Lens Review

John Riley reviews the wide-angle Tamron 20mm f/2.8 Di III OSD M1:2 FE mount lens, for full-frame Sony mirrorless cameras. Find out how it performs in this test.

|  Tamron 20mm f/2.8 Di III OSD M1:2 in Interchangeable Lenses
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Tamron has a trio of Sony E fit, full-frame prime wide-angle lenses that are small, light and very reasonably priced. A matching set comprising 20mm f/2.8 Di III OSD, 24mm f/2.8 Di III OSD and 35mm f/2.8 Di III OSD has to be an exciting proposition. Add to this a macro close focus magnification of half life-size and things start to look very interesting indeed. First off, let's look at the 20mm f/2.8 lens, coupled with the 42MP Sony A7R III camera body, and see what it can do.


Tamron 20mm f/2.8 Di III OSD M1:2 Handling and Features

Clearly, weighing in at a very modest 220g, there is an extensive use of plastics in the lens construction. This is not a negative point as the right sort of plastics can be effective and durable. In this case, the standard of manufacturing is excellent and the lens operates very smoothly. The front element is fluorine-coated to repel dust, moisture and grease and there is built-in moisture resistance to enable use in less than ideal weather conditions.

Starting at the front of the lens we have a dedicated petal lens hood that bayonets securely into position. There is no locking catch, but the hood shows no tendency to work loose anyway. The bayonet fit surrounds a standard 67mm filter thread. This size is common to all three lenses, offering a useful economy as only 67mm filters are needed for the set.

The only control on the lens is the manual focus ring and the function of this is, as usual, set on the camera body. The options are AF-S (AF Single Shot), AF-A (AF Auto), AF-C (AF Continuous), DMF (Direst Manual Focus – MF can be used while AF operational) and MF (Manual Focus). It is electronic in operation and utterly smooth in its action. The amount of resistance is just right. Focusing is down to 11cm, or 4.3 inches, a maximum magnification of 1:2, or half life-size. This is incredibly useful, allowing focusing as close as many macro lenses once did. Couple that with the ultra-wide 20mm focal length and many new possibilities arise for new perspectives on macro subjects. The only caution is that at the minimum focusing distance to 11cm (from the film plane) the front of the lens is only 2cm or so from the subject. This leaves little room for lighting so we do need to be careful that a shadow is not being cast on the subject. For the closest focusing, it may be useful to remove the lens hood to ensure there is some room to work.

Optical construction is 10 elements in 9 groups, including LD (Low Dispersion) and glass moulded aspherical elements. The diaphragm comprises 7 blades.

The term OSD means Optimised Silent Drive and refers to the AF motor. The AF is almost silent as we would expect, all but for the occasional slight sound if the focus point isn't grasped immediately. However, this is rare and most of the time AF locks on silently, quickly and accurately.

Finally, the metal mount is solid, but quite tight on this sample and it does not have the same silky feel as many lenses.

There are no particular vices when using the lens and it really is a pleasure to have such a compact, light optic at a time when many lenses are becoming ever faster in terms of maximum aperture, but ever larger and heavier as a consequence.


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Thanks for this review. I've got the 17-28/2.8 Tamron and the comparison of performance with this lens at 20mm shows a significant difference in sharpness and maybe, just maybe, justifying its addition.
30 Jan 2020 5:04PM
First you right "There is color fringing at the edges..." and looking at the samples I can indeed see very strong CA. But than you conclude "Well-controlled CA" ???
30 Jan 2020 5:15PM

Quote:Thanks for this review. I've got the 17-28/2.8 Tamron and the comparison of performance with this lens at 20mm shows a significant difference in sharpness and maybe, just maybe, justifying its addition.

The Tamron 20mm 2.8 was tested on the A7R III with 42 MP and the Tamron 17-28mm 2.8 on the A7 III with only 24 MP. Therefore the results are not comparable. With more MP the results can be much higher, but maybe with worse corner sharpness.

To the reviewers: Why do you review lenses on different cameras and making the results incomparable?
30 Jan 2020 6:01PM
In an ideal world there would be a universal camera body to test all lenses on, but sadly it depends upon availability of a suitable body and also when a lens is released. New, higher pixel counts are used now, but it would be impractical to re-test lenses reviewed on other lower pixel cameras. So, they are equated as far as possible by describing results as "excellent", "very good" or whatever, but it's not perfect for sure.
3 Mar 2020 8:36PM
I don't know how you can review a lens that has quite hefty CA and likely worst in class distortion (which has to affect the resolution numbers significantly when applied) and then rate performance as 5/5 stars. For the price it seems like it has reasonable performance, and sharpness seems good, but the distortion is so huge that even for landscape use, you're going to need to apply the distortion profile, which is going to impact that sharpness figure...if the sharpness wasn't evaluated with distortion corrected then it needs to be. a small amount of distortion can be fine, but huge distortion that basically requires correction on every shot should be a fairly major knock against the lens.

But despite these quite large flaws, you rate the lens not just good, but perfect with regards to performance. If this is a 5/5, where do all the wide-angles that are better fit?

That's not to say it isn't a good value...but have some objectivity here.
3 Mar 2020 11:08PM
Thanks for the question, which raises valid points. As regards the 5 stars for performance, this does not imply 100%, but implies it is within the top band of results. Within this band, there will still be variation, but we don't have a system that differentiates between, say, 88% and 96%. No lens is ever perfect.

The question of distortion is discussed in the section on performance, and it's an interesting one. By making the correction for distortion in-camera as opposed to in-lens no doubt there are advantages in the design and manufacture of the lens. This doesn't seem to affect the sharpness in this case and the figures provided are with the correction switched in. Without that, the testing becomes impractical. There are now many cases with many manufacturers where such corrections are built in and we can't switch them off. This does beg the question as to how the lens might behave in the future with cameras not designed with it in mind, but this too is mentioned in the text.

I hope that helps in explaining some of the thinking behind the evaluation of the lens for this review.
4 Mar 2020 2:18AM
Thanks for the update, and good to hear the resolution figures were with the distortion profile applied

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