On the Bench

This is the first review where we used Imatest software to analyze camera performance. Sorry to bombard you with so many figures and graphs, but I need to establish a baseline of data so that we will have a reference in future reviews.

Two of the Sigma lenses that were included for the review are considered to be wide angle at their shortest focal length, and one of the problems with wide angle lenses is falloff, or vignetting at the edges (the edges being darker than the center), so let's look at that first.

I photographed a blank white poster board for this test in the shade. All other bench test photos were taken in full sun, in the middle of the day.

For the 15mm-30mm lens, set to 15mm (wide angle), and at f/3.5 (the largest aperture for this lens), falloff was 1.6 f/stops at the edge. At f/8, this dropped to 0.6 f/stops.

At 30mm focal length, and f/3.5, falloff was reduced to 0.8 f/stops, and at f/8, it was reduced to 0.5 f/stops.

The 50mm lens had 0.7 f/stops falloff at f/2.8 (its largest aperture), and 0.25 f/stops at f/8.

For the 28mm-70mm lens, falloff was 0.9 f/stops at 28mm and f/2.8 (largest aperture), and 0.5 f/stops at f/8.

In telephoto (70mm), and f/2.8, falloff was 0.8 f/stops, and at f/8, it was 0.25 f/stops.

So, what you see here is that even with a telephoto lens (70mm), there is falloff. In fact, all lenses have falloff. It is just the matter of how much.

For comparison, here is an example from a Canon EOS-5D, with a 17mm-40mm lens (reasonably comparable to the 15mm-30mm Sigma lens). Falloff with the lens set to 17mm, and f/4.0 (largest aperture), was 3 f/stops. At f/8, it was 1.5 f/stops. The reason there is more apparent falloff than the Sigma 15mm-30mm lens is that the SD14 does not use all of the image field, while the Canon lens does.

At 40mm setting, f/4.0, falloff was 1.6 f/stops. At f/8, it was 0.6 f/stops.

For comparison with the snapshot camera market, using the Samsung NV10 which we reviewed some time ago, falloff in wide-angle mode, f/7.1, was 0.6 f/stops. In telephoto mode, falloff was 0.35 f/stops. This is better than either the Sigma or the Canon.

Go to Part VI.