Pentax 17-70mm Lens Comparison

The Sigma 17-70 F2.8-4.5 is a relatively large lens, at neatly 83 mm long and 79 mm wide at the front. Like many other Sigma lenses, it uses a surprisingly-large filter size of 72 mm. The front element does not rotate when focusing, facilitating the use of polarizers. It has seven aperture blades and it does not feature an aperture ring.

The Sigma lens does not bear the top-of-the-line EX branding, but is still very well-built. The mount is made of metal, and the lens body is all plastic. The finish is the standard Sigma “crinkle” texture, which looks more like a dark gray tone than a black one. The lens extends by a little over 4 cm when zooming to 70 mm, but focusing is internal, and the lens does not change its length when focusing. The lens shaft has double tubing, but no wobble was observed with our sample, even after four years of regular use.

The main part of the lens body (3.5 cm) is occupied by the zoom ring. This ring is well-textured, with a ribbed and rubberized surface and focal length markings. The ring is also very well damped.

The “Sigma DC” logo is placed on the focus ring, in gold letters, next to the lens name. The lens also has a zoom lock switch, preventing zoom creep. Again, after four years of use, the lens does not exhibit any zoom creep whatsoever, and the lock has almost never been used. This lock will only engage when the lens is at the 17mm position.

The front part of the lens is much larger than the rest of the body, a feature common on Sigma lenses. The area between the zoom ring and the front element is entirely taken up by the focus ring, which is approximately 2 cm wide.

The lens is provided with a petal shaped hood which reverses for storage. The inside of the hood is ribbed to prevent reflections. Using the focus ring with the hood reversed is all but impossible.

The maximum aperture varies with the focal length. The following table shows (approximately) how the aperture change with focal length.

The lens thus offers apertures wider than f/4 below 40 mm, and shifts to f/4.5 only at 70 mm.