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Lens review

Tamron 20-40 mm f/2.8 Di III VXD

19 July 2023
Maciej Lata││o

7. Coma, astigmatism and bokeh

Coma is practically not a problem on the smaller APS-C sensor but in the corners of full frame it makes itself felt. In case of 20 and 30 mm focal length you deal with its classic variant, as it turns the point-like diode images into a comma. Most of problems you can encounter at the maximum focal length – the comma is the biggest and it gets 'wings' that are a result of activating higher order aberrations.

As you see coma correction is hardly one of the Tamron's 20-40 mm finest features but it would be also difficult to call its performance abysmally bad. You deal here with levels that are on the borderline between medium and high.

Center, 20ámm, f/2.8 Corner APS-C, 20ámm, f/2.8 Corner FF, 20ámm, f/2.8
Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh
Center, 30ámm, f/2.8 Corner APS-C, 30ámm, f/2.8 Corner FF, 30ámm, f/2.8
Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh
Center, 40ámm, f/2.8 Corner APS-C, 40ámm, f/2.8 Corner FF, 40ámm, f/2.8
Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh


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Astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounted to 7.3% and it's a level considered by us as low. You can also notice some small differences between particular focal lengths. Astigmatism reaches its minimum at 30 mm and increases on both ends of the focal range.

Defocused circles of light don't look perfect but, taking into account the fact that you deal here with a zoom lens with ultra wide angles of view, it would be difficult to complain. The only feature that sticks out is a brighter rim. The areas inside the circles aren't perfectly smooth and even but also they come without many heterogeneities that could be called conspicuous. There are also no visible problems with mechanical vignetting because it disappears completely on stopping down the lens by 1 EV.

Center, 40ámm, f/2.8 Corner APS-C, 40ámm, f/2.8 Corner FF, 40ámm, f/2.8
Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh
Center, 40ámm, f/4.0 Corner APS-C, 40ámm, f/4.0 Corner FF, 40ámm, f/4.0
Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh
Center, 40ámm, f/5.6 Corner APS-C, 40ámm, f/5.6 Corner FF, 40ámm, f/5.6
Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh Tamron 20-40 mm f/2.8 Di III VXD - Coma, astigmatism and bokeh