Tamron 17-70 sharpness / field curvature issues

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Canon2018 Forum Member • Posts: 90
Tamron 17-70 sharpness / field curvature issues

I have tested many different lenses over the years and was often surprised by their performance in different situations. I really tried to like the Tamron 17-70 for its useful focal range. When testing this lens against Sony's 16-55 I found it to struggle more with field curvature. Using the same settings, focusing on a distant object @F/8, everything was in focus with the Sony while the pictures taken with the Tamron were equally sharp in the middle but not necessarily in the foreground of the frame or on the edges where distant objects did not present a flat surface. When I took a picture of a flat object, e.g. a building, the Tamron was perfectly sharp all across the frame, which means there was nothing broken or decentered. With distant objects edge sharpness was inconsistent. I never experienced this issue with the 16-55, which is tack sharp in all situations. Do you know how to overcome this problem? Would it help to focus on a different spot? For landscape shots, I generally focus on a distant object in the middle of the frame.

Below you will find a corner crop to illustrate the problem I experienced with Tamron's 17-70. The same picture appears perfectly sharp when taken with the 16-55

 Canon2018's gear list:Canon2018's gear list
Sony a6400 Sony E 10-18mm F4 OSS Sigma 56mm F1.4 DC DN | C (X-mount) Sony E 16-55mm F2.8 G Sony E 70-350mm F4.5-6.3 G OSS
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