How does the first third-party standard zoom for Sony full frame mirrorless cameras shape up? Michael Topham had the privilege to test the first working sample in the UK
Tamron 28-75mm f/2.8 Di III RXD review: Resolution, shading and curvilinear distortion
Our Image Engineering Tests reveals that the lens resolves its best sharpness in the centre towards the middle and far end of its zoom range. Inspect the solid red (28mm), green (50mm) and blue (75mm) coloured lines closely and you’ll notice that centre sharpness peaks at f/4 across the zoom range. The corners take a little while longer to sharpen up fully, with best results achieved from f/5.6-f/11, peaking at f/8. Sharpness starts to drop off beyond f/11 and users will want to take note that diffraction has the affect of softening images quite noticeably at f/16 and f/22.
Use the lens at any point in the zoom range at its maximum aperture and you’ll notice the corners appear darker than the centre of the image. Corner shading is less of a concern at around 50mm, but gets more obvious again as you push towards 75mm. Vignetting equates to a 1.2EV fall off in illumination at the wide end and 1.4EV at full telephoto. The good news is that this vignetting improves considerably by stopping the lens down to f/4 and becomes altogether less of a concern at f/5.6. Vignetting in shots taken at wide aperture settings can be alleviated by making sure in-camera lens corrections are activated.
It’s not unusual for standard zoom lenses to exhibit barrel distortion at their widest setting. This zoom is no exception and our tests reveals prominent barrel distortion, whereby straight lines bow outwards towards the edge of the frame. By the time you reach 50mm barrel distortion turns to pincushion distortion. This becomes obvious in shots taken of straight lines and is accentuated slightly more at the furthest point in the zoom range.