We’ve compared the Sony mount Sigma with the Sony Zeiss Vario-Sonnar T* 24-70mm f2.8 ZA SSM, a huge lens with an equally impressive optical construction and $1,599 price tag. We’ve also taken the opportunity to compare with it the Tamron SP AF 28-75mm f2.8 XR Di LD Aspherical [IF].
Although Tamron make a newer SP AF 24-70mm f2.8 Di USD (ultrasonic) model, the price is $1,299, yet the older lens is just a fraction of the cost at $499. Looking at the models it’s not an easy choice. The Sigma and Tamron perform quite similarly; although the former has higher central sharpness at the shorter focal lengths, the Tamron is the better performer of the two from 35mm to 75mm (at least up to f8).
The Sony Zeiss model on the other hand is without doubt the best, but wide open at 35mm and 40mm the Tamron isn’t so far behind. Stopping down just one stop to f4-5.6, however, soon shows the superior uniformity of Zeiss. Perhaps the biggest drawback with the Sigma is the high CA. At 24mm and to a slightly lesser degree at 28mm it’s noticeable in the corners at every aperture. The Tamron is untroubled by it but even the Zeiss has some at its widest.