Tamron 20-40 mm f/2.8 Di III VXD review - Autofocus and focus breathing

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Tamron 20-40 mm f/2.8 Di III VXD

19 July 2023

Maciej Latałło

10. Autofocus and focus breathing

Autofocus

The autofocus of the Tamron 20-40 mm joined ith the Sony A7R III is completely noiseless. When it comes to its speed we don't have any reasons to complain either. At the shortest focal length everything is very quick and running through the whole distance range with confirming the focus takes typically 0.4-0.5 of a second. In case of the maximum focal length focusing takes a bit longer but in the majority of cases it fits the range of 0.5-0.7 of a second.

When it comes to accuracy, we didn't experience any problems either. The lens performed properly well both outside and during our shooting session in the studio.

What's interesting, in case of the longest focal length we managed to notice a slight front focus tendency when we shot from closer distances.

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A7R III, 40 mm, f/2.8

Focus breathing

Focus breathing tests show reframing images as you oversharp them. We conduct the test by manually passing from the minimum focusing distance to infinity with the aperture stopped down; then we check how the field of view of the lens changed as a result. The test video of the tested Tamron lens is presented below:

Focus breathing, measured in this case at the maximum focal length, changes about 5% of the size of the frame. It is a more or less sensible value, noticeable in practice only when you change the whole distance scale very quickly. Unfortunately, when you deal with third-party lenses you don't get a possibility of focus breathing correction, available in the menus of newer Sony cameras and camcorders.