Tamron 28-75mm f2.8 DI v Sigma 24-70mm f2.8 EX
v Contax Zeiss 35mm f2.8
The motivation for this test was to establish whether a zoom could replace the 35mm Distagon f2.8 I commonly use for architectural shoots. Trolling about on location, the perfectly convenient lens for shooting exteriors would be a 35-70mm zoom that doesn't short change the 1Ds II optically, but unfortunately the world's best suffers from quite strong barrel distortion at the wide end - otherwise it is perfect.
I've had the Sigma 24-70mm f2.8 DG EX Macro for a while now, and really want to like it, despite its bulk and noisy autofocus. It seems sharp enough in everyday use, and it's a fraction of the cost of the Canon, but its strong and variable distortion also put it out of the picture for architectural use. Its natural competitor, then, is the Tamron 28-75mm f2.8 DI. Equally fast, much lighter and smaller and currently everyone's favourite lens.
But can it cut the mustard against the benchmark Distagon, only once outperformed thus far by its zoomier brethren - and only that for a gnat's hairsworth of resolution? With some trepidation, mindful of legion horror stories about Tamron's quality control, I opened the Tamron's box and went to work....
Test frames shot with a 1Ds II at ISO 100, RAW processed through C1 and saved for web with BoxTop Pro JPEG. Modest identical USM applied to each image. 100% crops shown.
Full frame / distortion test
Here's the full frame: familiar target. The Zeiss 35mm f2.8 is exemplary for controlling distortion with a little correctable barrelling, so it's the one to beat: mouse over each image to compare the rendering of the Tamron and Sigma zooms...