A 24-70mm lens is expected to have distortion – barrel at the wide end that transitions to pincushion at the long end. The Sony option, without the need for an adapter, would be expected to perform better from AF and frame rate perspectives. If you’re young and healthy and don’t mind an extra half pound of weight, the Sigma will pose no problem. If you’re doing what you can to lighten your camera bag, though, the Tamron may still be your best choice. Zoom Range

24-70mm F2.8 DG DN - SIGMA Corporation Support | 24-70mm F2.8 DG DN - SIGMA Corporation

The Sigma has a considerably more-modern overall design, though the Tokina has the rear-positioned zoom ring I prefer. Slight improvement is seen in the periphery at f/5.6, but across the frame image quality is very good at f/4.Results are much better at f/4, but the corners are still quite soft until f/5.6 where this lens is, again, sharp across the frame. Sealing: yes, a rubber grommet at the lens-mount plus further special weather-sealing throughout the construction. The other lenses in this comparison are similarly equipped except for the Tamron which only has a sealing at the lens-mount. [+] Full frame DSLR users will see some CA (Chromatic Aberration) affecting frame corners, especially at the extents of the focal length range. Exceptions to that description include 24mm where the Tamron is slightly better in the periphery and at 70mm where the Sigma perform slightly better over most of the image circle. In the end, I prefer the Sigma 24-70 f/2.8 over the Tamron in almost every aspect except for the size and weight where I prefer the Tamron to such a massive degree that it would really make this a difficult choice for me.

SIGMA 24-70mm 2.8 DG HSM OS | Art SIGMA 24-70mm 2.8 DG HSM OS | Art

At f/4, the center shows slight improvement, but the mid and periphery show noticeable improvement.

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Our results show that sharpness is slightly improved overall, especially when used wide-open at f/2.8 from corner to corner and at the mid- and longer focal lengths where large-aperture zooms tend to struggle (even high-grade models). The hood is strong molded plastic-constructed with only a slight amount of flex (which is good for absorbing impact). Autofocus was quite a pleasant experience with the Leica 24-70mm, and as a bit of a teaser to our comparison to the Sigma lens, I found that every aspect of Leica’s lens responded faster than Sigma’s on the SL2. Leica told us that it expected performance to be better with a Leica to Leica interaction, and while I admit I wasn’t quite sure I believed that then, I certainly believe it now. The acutance profile below shows the sharpness profile of the three lenses at their longest focal length and at f/2.8. Closing down the apertures increases sharpness to f/5.6-8, whereas after at f/11, all three begin to exhibit some diffraction and score below 70% acutance. At the same time, the Tamron uses the 67mm filter threads like all of the f/2.8 zoom lenses in their lineup, while the Sigma utilizes the same massive 82mm filter threads as the Sony GM.

Sigma 24-70Mm F/2.8 Dg Dn Full Frame Lens for Sony E Mount Sigma 24-70Mm F/2.8 Dg Dn Full Frame Lens for Sony E Mount

Sigma has provided just the right amount of resistance on the manual-focusing ring, but the zoom ring is a shade on the heavy side. The focused-distance window includes markings that indicate depth-of-field for the 24mm focal-length setting but there are no markings for other focal lengths. Although alternatives to the Sigma 24–70mm F2.8 DG DN Art lens differ depending upon whether you're an E-mount or L-mount shooter, it's a very solid offering for either mount. Its pricing simply blows manufacturer offerings from Sony and Panasonic out of the water, and despite its high-end build and performance, it's not a whole lot more expensive than consumer-grade offerings for either mount.The graph below shows the degree of corner shading visible in images from the three lenses at their longest focal length and widest aperture (when it will be most noticeable). The Tokina has about .5 stops less peripheral shading at f/2.8, though stopping down largely eliminates this difference. I'm just getting started into the list of uses for this lens and the range of video uses for this lens is as broad as for stills.