whichlens.com - Lens Reviews

This is a test between the popular Tamron 28-75mm f/2.8 and the seemingly unnoticed Sigma 28-70mm f/2.8 that was recently released. The Tamron is popular favorite because of its excellent optics, low price and manageable size. The Sigma is clearly a wannabe usurper with an even lower price, even smaller size and hopefully better optics? Read on and find out.

BUILD
The two lenses are well built and nothing less than you’d expect in this price range. The Sigma has the trademark Sigma peach finish which makes it nice to grip but does wear over time. The Sigma is slightly shorter than the Tamron but has a similar diameter. Both use 67mm filters.

AUTOFOCUS
One of my main criticisms of the Tamron is that the autofocus can be a little too leisurely. It takes a full 1.6 seconds from shutter press for the Tamron to rack from infinity to closest focusing distance and bank to infinity again. The Sigma on the other hand, takes only 0.8 seconds. However, this dramatic difference is not the whole story. The real world focusing test of focusing on one object, then moving on to one further away, then another even further away and the back to the original object shows the Tamron is actually only very slightly slower than the Sigma. Furthermore, the Sigma hunts more than the Tamron which puts the Sigma slower in certain circumstances. Finally, the Sigma AF motor is louder and has a more pronounced grinding sound than the Tamron motor does. It is difficult to call a clear winner here, but I would have to give the edge to Tamron because it doesn’t hunt like the Sigma does. The motor is also more discreet than the Sigma, which is a bonus.

OPTICAL QUALITY
Samples
These two lenses are so close that the 50% crops I produced for the website are virtually useless. The usual compromises show themselves. Softness at f/2.8 and f/16. Best sharpness at either f/4 or f/8. I did my analysis at 200%. At 28mm, they are equals. At 35mm, 50mm and 70/75mm, the Tamron is very slightly sharper at all aperture values. However, the difference is very slight and I doubt it would be noticeable in real world conditions. The Sigma’s color balance is slightly warmer than the Tamron, a trait common to their lenses. I would rate both as very sharp lenses. I made comparisons to my 35mm f/2 and 50mm f/1.4 primes and while the two zooms aren’t as sharp as the two primes, the difference is slight and shows mostly at wide apertures.

CONCLUSION
This is both a case of “you get what you pay for” and the law of diminishing returns. At the time of writing, the Sigma can be had for as low as $270 and the Tamron is $360 with a $40 rebate available as well. The difference buys you less hunting on autofocus, a more discreet autofocus motor, an extra 5mm telephoto reach and very slightly greater sharpness. I think as far as great sub $300 lenses go, the Sigma is the way to go, but if you can stretch an extra $50 and don’t mind dealing with the hassles of rebates, the Tamron is still the king of the hill. Of course if you are all about quality and money and portability is no issue, you should just suck it up and get the Canon 24-70mm L at $1,200.