Pentax 17-70mm Lens Comparison
Sigma 17-70 v2: Construction
The Sigma 17-70 v2 is larger than the previous iteration, at neatly 89 mm long and 79 mm wide at the front. Like many other Sigma lenses, it uses a surprisingly large filter size, at 72 mm. The front element does not rotate when focusing, facilitating the use of polarizers. It has seven aperture blades. It does not feature an aperture ring. It feels larger and heavier than the previous version.
The Sigma lens does not bear the top-of-the-line EX branding, but is still very well made. The mount is made of metal, and the lens body is all plastic. The finish is smoother than the previous version of the lens, and feels durable. 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.
The main part of the lens body (3.5 cm) is constituted by the zoom ring. This ring is well-textured, with a ribbed and rubberized surface and focal length markings. The ring is 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. This lock will only engage when the lens is at the 17 mm position.
Next to the lock are two new switches that weren’t present in the first version. The first activates the image stabilization system (which Sigma labels OS) and the second toggles between manual and auto focus.
The front part of the lens is the same size as the previous version, but the center part of the body is about as large as the front element, while it was narrower in the version 1. The area between the zoom ring and the front element is taken up by the focus ring, which is approximately 2 cm wide. The part between the camera body and the zoom ring is longer, and hosts the two new switches.
The lens ships 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 the aperture change with focal length.
| Focal length (mm) | Aperture |
| 17 | f/2.8 |
| 23 | f/3.2 |
| 34 | f/3.5 |
| 70 | f/4 |
The lens has different steps than the previous version, and is faster than the Pentax 17-70mm below 70mm.
The lens makes a soft sound when the camera is powered up and when it is turned off; presumably these are the OS and HSM gears engaging.
