Tamron 17-50 mm f/4 Di III VXD
8. Vignetting
| A7R IIIa, APS-C, 17 mm, f/4.0 | A7R IIIa, APS-C, 17 mm, f/5.6 |
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| A7R IIIa, APS-C, 33 mm, f/4.0 | A7R IIIa, APS-C, 33 mm, f/5.6 |
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| A7R IIIa, APS-C, 50 mm, f/4.0 | A7R IIIa, APS-C, 50 mm, f/5.6 |
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In this case there are no serious problems at any focal length. Applying the ultra wide angle of view and f/4.0 aperture you have to take into account a loss of 17% (−0.53 EV) of light in the frame corners. Stopping down the aperture doesn't make any significant difference because by f/5.6 and f/8.0 we got the same result of 15% (−0.48 EV).
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In the middle of the focal range the situation is even better because already at the maximum relative aperture vignetting is practically imperceptible, reaching only 9% (−0.28 EV).
At the maximum focal length and f/4.0 aperture vignetting is just 13% (−0.40 EV) and it drops to an imperceptible level of 6% (−0.17 EV) on stopping down the lens to f/5.6.
Now let's see how the tested lens deals on full frame – appropriate images you can find below.
| A7R IIIa, FF, 17 mm, f/4.0 | A7R IIIa, FF, 17 mm, f/5.6 |
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| A7R IIIa, FF, 33 mm, f/4.0 | A7R IIIa, FF, 33 mm, f/5.6 |
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| A7R IIIa, FF, 50 mm, f/4.0 | A7R IIIa, FF, 50 mm, f/5.6 |
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At the most difficult combination of ultra wide angle and f/4.0 aperture the problems are enormous, with vignetting reaching as high as 75% (-4.03 EV). Still, the performance is worth analysing in more detail with the help of a graph below.
It's clear that, as you move away from the centre of the frame, brightness loss is quite slow up to a distance of about 70-75% from the centre. Then there is a change of inclination and the decrease becomes noticeably faster. Still you have to remember the fact that the lens provides you almost 8 deg of field to spare and it can be used in distortion correction. After the correction you reach the declared value of the field but, at the same time, you cut out the corners of the frame with the highest level of vignetting. As a result, it shouldn't exceed 60%.
By f/5.6 aperture vignetting decreases to 66% (−3.08 EV), by f/8.0 it drops further to 55% (−2.33 EV), and by f/11.0 to 47% (−1.84 EV). Further stopping down doesn't produce any measureable effects.
In the middle of the focal range the performance improves distinctly. By f/4.0 light fall-off in the frame corners amounts to 27% (−0.91 EV) and it decreases to 24% (−0.78 EV) on stopping down the aperture to f/5.6. By f/8.0 and f/11.0 apertures we got the same result of 22% (−0.72 EV).
At 50 mm focal length you still deal with a moderate level because at the maximum relative aperture it amounts to 25% (−0.83 EV), by f/5.6 it drops to 15% (−0.46 EV), and by f/8.0 it decreases slightly even more, to 14% (−0.44 EV).
| Sony A7R IIIa, 17 mm, f/4.0 |
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| Sony A7R IIIa, 33 mm, f/4.0 |
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| Sony A7R IIIa, 50 mm, f/4.0 |
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