Lens review

Sigma A 24-70 mm f/2.8 DG OS HSM

28 July 2017
Arkadiusz Olech

3. Build quality and image stabilization

The following chart presents a comparison between the tested lens and other 24-70 mm f/2.8 devices. Only the Nikkor and the Tamron, like the Sigma, are stabilized. On the other hand the Sigma and the Nikkor are most optically complex and the heaviest of all – both weigh a bit over 1 kilo. Still the sensible dimensions of the new Sigma are worth noticing - it is notably shorter than the Nikkor, a bit smaller than the Tamron and also smaller than the non-stabilized Canon. The Sigma prevails in this group when it comes to the minimum focusing distance but still the Sony Zeiss remains unbeatable in this category and it also has the smaller filter diameter. The Tokina looks the poorest, with the lowest amount of elements, without any optical image stabilization unit or an ultrasonic autofocus motor.

In the photo below we positioned the Sigma A 24-70 mm between the Sigma A 35 mm f/1.4 DG HSM and the unstabilized Nikkor AF-S 24-70 mm f/2.8G ED.

Sigma A 24-70 mm f/2.8 DG OS HSM - Build quality and image stabilization

The tested lens starts with a metal mount and a rubber gasket; the mount surrounds contacts and a rear element which is less than 27 mm in diameter. The element is positioned on the same level as the mount at 24 mm and it hides inside the barrel about 2.5 mm deep when you pass to the 70 mm focal length. That movement creates quite a big slit in the rear tube through which you can glance some parts of the interior. Still it must be said that the inside of the barrel is blackened very well, matted and ribbed too.

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Sigma A 24-70 mm f/2.8 DG OS HSM - Build quality and image stabilization

The proper body of the lens starts with a smooth, black, metal ring on which you can find a white dot making an alignment with a camera easier, an inscription „017” indicating the year of the launch and another inscription, „MADE IN JAPAN”. Further on you see a distance scale behind a window, expressed in feet and meters and below there are given basic parameters of the lens. On the left side of the scale is an „A” letter meaning the lens belongs to the „Art” group. Then you see a series of switches. The first one, FOCUS, controls the focusing mechanism mode, with three possible positions, AF, MO and MF. Apart from standard options (the ring still works even if you choose the AF mode) you also get the MO (Manual Overdrive) one. If you employ it the ring still works even if the autofocus is in the full-time mode. Further on you see an OS switch responsible for the optical stabilization unit (OS ON/OFF).

Sigma A 24-70 mm f/2.8 DG OS HSM - Build quality and image stabilization

Then you see two rings on the barrel. The first one, for manual focusing, is 18 mm wide, its middle covered by rubber ribbing. It moves smoothly, without any slacks and is properly damped. Running through the whole distance scale takes a turn through an angle of 90 degrees. It is a typical value for autofocus lenses but it doesn't ensure precise manual settings. The second ring, 30 mm wide, controls the focal length; most of its surface cover rubber ribbing and above you see focal length marks at 24, 28, 35, 50 and 70 mm.

Sigma A 24-70 mm f/2.8 DG OS HSM - Build quality and image stabilization

When you change the focal length the front element system extends on a smooth, plastic tube, increasing the dimension of the lens by 33 mm. The front element itself is 70 mm in diameter, quite flat, surrounded by a non-rotating filter thread, 82 mm in diameter, and a hood mount.

Sigma A 24-70 mm f/2.8 DG OS HSM - Build quality and image stabilization

The optical construction of the tested Sigma consists of 19 elements positioned in 14 groups. Among them you can find three low disperions elements made of SLD glass and four aspherical ones. Inside you can also find a round aperture with nine diaphragm blades which can be closed down to a value of f/22 at the maximum. The front element is covered by water and oil-repellent coating to make its cleaning easier.

The lens cooperates with the USB DOCK personalizing device and with the Sigma MC-11 mount converter. Because of that users of Sony (E) cameras have a possibility to attach Canon EF mount lenses to their cameras preserving fully active AF system and EXIF-type information flow.

Buyers get both caps, a petal-type hood and a hard case for the lens in the box.

Sigma A 24-70 mm f/2.8 DG OS HSM - Build quality and image stabilization

Optical stabilization

Sigma declare that the compensation of their Vibration Reduction system of the new 24-70 mm model amounts to 4 EV. In order to check that claim we took several dozen photos at 70 mm focal length with times of exposure ranging from 1/80 to 1/2 of a second and the stabilization switched on and off. For every set of photos we determined a percentage of blurred shots and presented it as a function of exposition time expressed in EV (0 EV being the equivalent of 1/60 of a second). An appropriate graph you can find below.

Sigma A 24-70 mm f/2.8 DG OS HSM - Build quality and image stabilization

The maximum distance between two curves is the measure of the optical stabilization efficiency of the tested lens. In this case it is near 3.3 EV so a bit short of those declared 4 EV. Still the result we find sensible enough, similar to the performance of the rivals - in the case of the Nikkor we got 3.5 EV and in the case of the Tamron 3.0 EV.