The Sigma 30mm F1.4 EX DC HSM ($690 list) is the APS-C version of the classic fast 50mm lens that, before the popularity of zoom lenses, was the standard lens paired with 35mm SLRs. This lens is a little shorter than 50mm on an APS-C camera?its field of view is more like that of a 45mm, which is closer to a true normal perspective. It is available for Sigma, Canon, Nikon, Sony/Minolta, Pentax, and Four Thirds cameras.
The lens itself is short and squad, measuring 2.3 by 3 inches (HD) and weighing 15.2 ounces. Its front element is rather large for a prime lens, requiring the use of 62mm filters.? It's a lot bigger and heavier than the Nikon AF-S DX Nikkor 35mm f/1.8G ($199.95) lens, which is 2.1 by 2.8 inches in size and weighs only 7 ounces?at the cost of only a half-stop of light gathering capability.
I used Imatest to measure the image quality produced by this lens when paired with the Sigma SD1 Merrill . The results were disappointing. At f/1.4 it netted only 1,220 lines per picture height, well shy of the 1,800 required for a sharp image. The center portion of the photo was sharp at 1,900 lines, but the sharpness quickly drops as you move away from the middle of the image. It improves to 1,550 lines at f/2, and finally hits 1,868 lines at f/4. The lens is sharpest at f/5.6, where it records 2,042 lines, but by that point you've lost the ability to create a really shallow depth of field. Distortion is also an issue with this lens?it produces 1.8 percent barrel distortion, which is really too much for a standard-angle prime lens.
The real appeal of the Sigma 30mm F1.4 EX DC HSM is its fast f/1.4 aperture. Unfortunately, shooting at this setting gives you images with very soft edges and corners, so you'll need to compose your images with that in mind. The lens is pretty usable, but not tack sharp, at f/2, but at that point you can consider an f/1.8 or f/2 lens of an equivalent focal length in the camera mount of your choosing. Generally speaking, these lenses are generally smaller, lighter, and less expensive.
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