Unless you’ve been hiding under a rock, you’ll have heard of the new Sigma 18-35mm F1.8 DC HSM A lens that’s now available. This is a really exciting lens as it’s the first to have a such a wide fixed aperture of f/1.8 across the whole zoom range.
We had an opportunity to do a few tests with Reikan FoCal and one of these lenses yesterday, and the results match up with the excellent reviews this lens has been having. This is by no means a full review, just the results of couple of quick tests we had a chance to run with this shiny new lens.
Aperture Sharpness and Focus Shift
First off, the Aperture Sharpness/Focus Shift test. Tthe copy of the lens we tested is sharpest at around f/3.2, but it’s still very sharp wide open without much drop off in image quality at all (you can see this by the fact that there isn’t much of a curve between the diffraction limited aperture (the red line), and the far left point which shows the quality at f/1.8).
Focus shift is shown on this graph by a difference in position between the diamond markers and the square markers, and on this chart they pretty much overlay, which means this lens exhibits no focus shift. So you can be sure you’re getting the sharpest shot even when shooting stopped down (for more information about Focus Shift take a look at this article, which includes examples of how it affects images).
The performance of this lens across the aperture range is excellent, reflecting what we’ve seen from the latest Canon lenses (e.g. the EF 24-70 f/2.8L) which are far more expensive.
(Note that this test is not available in the current version of Reikan FoCal, but will be coming soon…)
Focus consistency shows how well a camera and lens combination will focus on the same spot when multiple pictures are taken. The performance of the Sigma 18-35 f/1.8 lens on a Canon 7D body is very good to excellent, with a Consistency of Focus of 98.6% (anything over 98% is considered very good). The chart below shows the results for the test, with all points scoring within 3% of the best point. In real use, this equates to negligible difference between shots.
This is just 2 quick tests with FoCal, but the Sigma 18-35mm F1.8 DC HSM A lens has shown excellent relative sharpness across the aperture range and reliable autofocus consistency. We’ll be testing in more depth soon, but in our opinion this lens is certainly living up to the rave reviews that have been published!