Studio Tests (APS-C)

The Tamron SP 24-70mm F/2.8 Di VC USD performs exceptionally well on APS-C in the studio, coming remarkably close to the much more expensive, and unstabilized, Canon EF 24-70mm f/2.8L II USM tested on the same body. It also matches or surpasses the older designs from Nikon, Sony and Sigma. The only blips are slightly soft edges wide open at 35mm, and rather strong barrel distortion at wideangle.

Sharpness Sharpness is very impressive indeed - in fact the Tamron is one of the best performers in its class. It's very sharp in the centre wide open at all focal lengths, although there's a slight drop-off towards the edges at intermediate focal lengths. In general the best results are obtained around a stop either side of F5.6, with diffraction starting to soften the output from F11 onwards. As usual on APS-C, F22 is best avoided unless extreme depth of field is essential.
Chromatic Aberration Chromatic aberration is overall pretty well controlled, and unlikely to be a problem in normal use. As expected it's most visible at the extremes of the zoom range, with a little green/magenta fringing at wideangle and red/cyan at telephoto.
Vignetting Vignetting is negligible, as usual for a full frame lens used on APS-C.
Distortion Distortion relatively high at 24mm, with visible barrel distortion even on APS-C cameras - other lenses in this class tend to do a bit better. But it reduces on zooming in, and from 35mm onwards is essentially a non-issue.

Macro Focus

Macro (APS-C) - 102x68mm coverage
Measured magnification: 0.22x
Distortion: Very slight barrel

Minimum focus distance*: 34.8 cm
Working distance**: 16.2 cm
Focal length: 70mm (112mm equiv)
* Minimum focus is defined as the distance from the camera's sensor to the subject
** Working distance is measured from the front of the lens to the subject

The Tamron 24-70mm continues to perform pretty well on APS-C cameras towards its minimum focus distance. It's quite obviously soft at F2.8, but improves dramatically on stopping down to F4, giving decent cross-frame sharpness. The best results in terms of sharpness are obtained from F8 to F16; F22 gives noticeable diffraction softening. There's a little lateral chromatic aberration, but not much, and just a hint of barrel distortion. Overall this means the Tamron gives better results close to its minimum focus distance than we found from the more expensive Canon EF 24-70mm f/2.8L II USM.

Specific image quality issues

As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. Here we're looking at issues specific to APS-C users; for a fuller picture, be sure to read the next two pages too.

Chromatic Aberration

Chromatic aberration is generally very low on APS-C bodies, and only really visible at the wide end of the zoom. The example below shows what you can typically expect - it's clearly visible, but not too objectionable even without any correction. It can, as usual, be eliminated more-or-less completely using appropriate RAW processing.

Lateral Chromatic Aberration - Canon EOS 650D, 24mm F8
Camera JPEG RAW file converted in Adobe Camera Raw
100% crop, lower right 100% crop, lower right, CA corrected