Compared: Canon 28mm f/1.8 USM and Sigma 30mm f/1.4 EX DC HSM
by Jeremy Rosenberger
In February 2005, Sigma announced an intriguing lens--a 30mm f/1.4 "DC" format--"DC" referring to a reduced image circle suitable for digital cameras with APS-C-sized sensors. On such cameras, the lens offers a "normal" field of view approximating that of a 50mm lens on a "full frame" 35mm camera. SLR camera giants Canon and Nikon so far seem to have ignored the "50mm equivalent" for crop-factor cameras (although in their defense, 28mm and 35mm lenses are at
least in the ballpark).
As an owner of a Canon 28/1.8 and an addict of big apertures, I found myself wondering how the 30 would stack up, particularly in terms of sharpness. The 28 is the lens I reach for most often (it serves as a "normal" lens on my Digital Rebel XT), and while I'm quite fond of it, I was tempted by the extra 2/3 stop offered by the Sigma. There is of course Canon's 35mm f/1.4L, but its price is prohibitive for many of us hobbyists, and at a 56mm field of view when used with the XT, it's a little on the long side. So I set out to determine whether Sigma could dethrone my current favorite, and acquired a copy of the 30 to put the two to the test.
I'm not a professional tester of photographic equipment, nor am I the most demanding user. But I wanted to devise a meaningful test, so I was reasonably careful in the test methodology: I mounted the camera (the 8MP Digital Rebel XT) on a tripod, enabled mirror lock-up and used a remote shutter release. At each aperture setting, I took three shots with each lens and picked the best of the three to mitigate any camera shake that may have occurred. Also, rather than take pictures of a newspaper or some other subject that nobody photographs in real life, I tried to choose a photographically interesting subject.
All shots were taken at the camera's full 8MP resolution, ISO 100, "sunny" white balance, aperture priority, in RAW format, using light from a nearby window. (Because the light wasn't entirely controlled, there are minor exposure variations from shot to shot.) The apertures chosen were f/1.4 (the Sigma's maximum), f/1.8 (the Canon's maximum), f/2 through f/16 in one-stop increments (f/16 being the Sigma's minimum), and f/22 (the Canon's minimum).
I used the center autofocus point, letting the camera autofocus with each shot; incidentally, there were no focus misses with either lens. It has been argued that this methodology "tests" the AF system rather than absolute lens sharpness. While I completely agree, keep in mind that the purpose of this test is to ascertain the performance of these lenses in typical use--autofocus tolerances and all.
The shots were post-processed using Capture One LE using modest sharpening and noise suppression parameters:
- Method: Standard look
- Amount: 50
- Threshold: 3
- Noise suppression: 2 (Low=1, High=4)
- Color Noise suppression: 15
- Banding suppression: 2 (Low=1, High=4)
In addition, I dialed in a bit of negative exposure compensation to the Sigma frames "after the fact"--see the analysis for an explanation.