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Lens review

Tamron 20 mm f/2.8 Di III OSD M 1:2

27 March 2020
Maciej Latao

8. Vignetting

First let's check the Tamron's vignetting on the smaller APS-C sensor – appropriate thumbnails you can find below.

A7RII, APS-C, f/2.8 A7RII, APS-C, f/4.0
Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting


The aberration is completely visible at the maximum relative aperture, where it reaches 32% (−1.12 EV). It's a lot, after all we are speaking about the smaller APS-C sensor. Vignetting makes itself felt also by f/4.0, where it amounts to 21% (−0.70 EV), and it becomes practically imperceptible by f/5.6, where we got a result of 14% (−0.45 EV).


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Now let's check the situation on full frame by glancing at thumbnails below.

A7RII, FF, f/2.8 A7RII, FF, f/4.0
Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting
A7RII, FF, f/5.6 A7RII, FF, f/8.0
Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting


In this case the results are simply bad. By f/2.8 brightness loss in frame corners amounts to as much as 63% (−2.89 EV). What's more, stopping down helps a bit but not as much as we wish it would. By f/4.0 the aberration still reaches a very high level of 53% (−2.20 EV), by f/5.6 it decreases to 47% (−1.87 EV), and by f/8.0 it drops to 41% (−1.53 EV). Also by f/11.0 and f/16 you can notice a slight decrease, with the following results: 36% (−1.28 EV) and 35% (−1.25 EV).

Sony A7RII, JPEG, f/2.8
Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting
Below we present averaged out values of brightness loss shown in concentric circles as you move further away from the frame centre. The numerical value of every image, expressed in percents, shows an area limited from the top and right by 100% and from the bottom by the presented curve. The area indicates how much light overall is lost due to the vignetting effect. Please, don’t mix these percentages with the values given at the beginning of the chapter because they aren’t directly connected.

Tamron 20 mm f/2.8 Di III OSD M 1:2 - Vignetting

f/2.8 f/4 f/5.6 f/8