Today I have a couple of shots for you in the form of animated GIF to highlight the levels of distortion and vignetting present in the Tamron SP 24-70mm f/2.8 Di VC USD.
In each sequence I’ve used the lens wide open, since this is where vignetting is at its strongest. These were taken with a full frame camera, which means it’s more apparent than it would be when using the lens in conjunction with a cropped sensor (click on each image and count to five…)
For the corrected images, I’ve used Adobe Camera RAW lens correction profiles, which is a one-click solution to both issues. DXO Optics does a similar job, and is every bit as easy. These days I don’t see vignetting as a major issue because of the ease of correcting it in software, but it is worth pointing out that vignetting is particularly strong in this lens compared to models by other manufacturers.(probably due to the larger-than-average size of the front element). Of course, there will always be those who like to see a bit of corner shading, so if you like to add vignettes (perhaps to portraits) then this may be an advantage to you.
Both vignetting and barrel distortion are more obvious at the wide end of the lens. In fact, due to the apparent enlarging of the 70mm image caused by the crop that automatically follows the corrections applied by the Adobe profile, it’s very hard to see how the distortion manifests at the wide end.
In practice, the vignetting improves very quickly when stopping down the aperture, which means that it is can be used as a creative choice if required.
For most landscapes, the distortion won’t be an issue either, but it is can be noticeable when shooting geometric shapes or buildings. It’s probably this that makes the distinction between marque lenses and the Tamron. If lack of distortion is the most important thing for your work (to a point that software is insufficient), then I’d imagine that the only thing that will really make you happy is a tilt-shift prime lens.
However, the Tamron is still an incredibly sharp lens capable of resolving a level of detail on a par with Nikon and Canon models, and as this one runs about £300-400 cheaper than its cousins and adds an excellent stabilisation feature not currently available in its counterparts, you will have to decide which is more important to you.