DL Editor's choice
In April, Sigma stunned the realm of photography when it announced the world's first zoom lens with a constant f/1.8 maximum aperture across its 18 to 35mm zoom range.
On the other hand, imaging giants such as Canon and Nikon can only offer wide-angle zoom lens of the same range at a smaller constant f/2.8 aperture.
These original lenses also tend to be expensive. Canon's EF16-35mm f/2.8 II USM lens costs nearly $3,000. Sigma's wonder lens costs $1,188.
On the downside, the Sigma lens lacks a built-in image stabiliser. But you do not really need one when you can shoot at such a large aperture. I usually turn off the built-in stabilisers of my lenses, as I find they impede autofocusing (AF) speed.
For many, a far greater drawback will be the lack of support for a full-frame DSLR. The Sigma is meant for APS-C DSLRs, as its image coverage is the size of an APS-C image sensor.
For this review, I used my Canon EOS 7D with the Canon mount version of the Sigma lens. Because of the 7D's 1.6x crop factor, the range effectively becomes 28.8 to 56mm.
When you hold the lens, it gives you a confident feel with its solid blend of metal and Sigma's Thermally Stable Composite or TSC polycarbonate. This is supposed to be stronger and lighter than conventional polycarbonate.
However, the lens is no featherweight at 810. But for a lens with constant f/1.8, I would gladly accept this burden.
The Sigma lens balances well with the body of my 7D with vertical grip. But if it is used with a lighter DSLR body, such as the Canon EOS 100D, the set-up may end up front heavy.
The design is quite conventional, with a manual focusing ring right in front and a zoom ring closer to the lens mount.
The distance scale and focus mode switch are sandwiched between these two rings. Unlike in lenses that extend and retract during zooming, the zooming mechanism is internal so the lens stays the same length at all times.
AF is instantaneously spot-on in bright sunlight. Even in almost total darkness, it is able to lock on to a focus in less than a second with the aid of the AF assist light.
With other lenses, when one shoots at f2.8 or larger apertures (that is, lower f-stop numbers), the resulting images tend to be a bit soft at the edges.
Not so with the Sigma. At f/1.8, the edges look sharper than those shot with other lenses at a similar aperture size. Such sharpness improves further when you reduce the aperture to f/4.
There is slight distortion at 18mm but there is no visible distortion at 24mm and above. It also exhibits very little chromatic aberration and vignetting.
The Sigma 18-35mm f/1.8 DC HSM is an impressive fast lens with a bigger constant aperture than any original zoom lens you can find. For APS-C DSLR users, this is the lens to buy.
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