Tamron 28-75 mm f/2.8 Di III VXD G2
7. Coma, astigmatism and bokeh
The situation changes a bit at the longer end of the focal spectrum where the influence of coma becomes noticeable as a slight lengthening of point-like sources of light. Fortunately this effect is not high as the level of this aberration belongs to the borderline between low and medium values.
| Center, 28 mm, f/2.8 | Corner APS-C, 28 mm, f/2.8 | Corner FF, 28 mm, f/2.8 |
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| Center, 50 mm, f/2.8 | Corner APS-C, 50 mm, f/2.8 | Corner FF, 50 mm, f/2.8 |
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| Center, 75 mm, f/2.8 | Corner APS-C, 75 mm, f/2.8 | Corner FF, 75 mm, f/2.8 |
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Astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounted to 5.2% and it is a value positioned on the borderline between very low and low levels. Still, the differences between particular focal lengths are conspicuous. At 28 mm you deal with a value of 4.7%, at 50 mm it is barely 1.6% , but at the 75 mm focal length astigmatism increases to 9.2%.
Defocused circles of light are a very nice surprise. There are as many as two aspherical elements inside this lens but you don't notice any distinct onion-ring bokeh, quite the opposite is true, this phenomenon is here reduced to mere traces, definitely lower than in the case of the predecessor. The fact that mechanical vignetting disappears on stopping down the aperture by 1 EV, a noticeable improvement compared to the previous version which showed truncated circles of light even after stopping down by 2 EV, also should be praised. It is a significant progress.
| Center, 75 mm, f/2.8 | Corner APS-C, 75 mm, f/2.8 | Corner FF, 75 mm, f/2.8 |
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| Center, 75 mm, f/4.0 | Corner APS-C, 75 mm, f/4.0 | Corner FF, 75 mm, f/4.0 |
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Center, 75 mm, f/5.6 | Corner APS-C, 75 mm, f/5.6 | Corner FF, 75 mm, f/5.6 |
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