Sigma เปิดตัวเลนส์ 18-35mm-F1.8-DC-HSM

Preview based on a pre-production Sigma 18-35mm F1.8 DC HSM

Sigma has a long history as a lens maker, having been founded over 50 years ago. In the film era it was best known for relatively inexpensive lenses that undercut the camera makers’ own equivalents in terms of price. But this has changed over the part decade or so; while other companies have shifted manufacturing to cheaper locations such as China and Thailand, Sigma has stubbornly refused to move from its factory in Aizu, Japan. This means it can no longer compete in the same way on price alone, and it’s therefore switched its focus towards higher-value offerings.

Over the past few years we’ve seen increasingly ambitious concepts appear from the company’s design studios. The original (and recently-replaced) 30mm F1.4 EX DC HSM has long been one of our favourite lenses for APS-C SLRs, and the 50mm F1.4 EX DG HSM grabbed our attention back in 2008 due to its sharpness at large apertures. Most recently the 35mm F1.4 DG HSM impressed us with its exceptional optical quality at a very competitive price. This all bodes well for the company’s latest offering – the record-breaking 18-35mm F1.8 DC HSM, which is the first constant F1.8 SLR zoom lens to hit the market.

Sigma’s choice of F1.8 as maximum aperture isn’t a coincidence; it means that the lens will offer the same control over depth of field as an F2.8 zoom does on full frame. What’s more, it will also offer effectively the same light-gathering capability as an F2.8 lens on full frame. By this we mean that it will be able to project an image that’s just over twice as bright onto a sensor that’s slightly less than half the area, meaning the same total amount of light is used to capture the image. This is important as it’s a major determinant of image quality. Essentially it means that APS-C shooters will be able to use lower ISOs when shooting wide open in low light and get similar levels of image noise, substantially negating one of the key advantages of switching to full frame.

As we’d expect at this level, the lens uses an ultrasonic autofocus motor for fast, silent focusing. It’s compatible with Sigma’s new USB dock which allows you to fine-tune autofocus behaviour in much more detail than the AF microadjust corrections found on SLRs, which should help get the best possible focus accuracy and make the most of the large aperture. It also incorporates several of the thoughtful design touches that we were impressed by on the 35mm F1.4, including an improved AF switch, and a large grip area on the base of the barrel for better handling.

The lens’s 27-53mm equivalent focal length range is obviously a little limited, but should still be rather useful for such applications as wedding and events photography. So while it may not quite match the capabilities of a 24-70mm F2.8 on a full frame SLR, for existing APS-C users it should offer something very close. Sigma has said nothing yet about pricing, so while we expect the 18-35mm to be less expensive than buying a 24-70mm F2.8 and a full-frame body, the overall appeal of the lens is impossible to pin down precisely at this stage.

Overall though the 18-35mm F1.8 is certainly an intriguing product, and we applaud Sigma for pushing the boundaries of lens design ahead of the more conservative camera manufacturers. It’s a lens we think is worth investigating in more detail, and we’ll be reviewing it just a soon as we can lay our hands on a shootable copy. Until then you can read more about the lens’s design and operation on the next page of our preview.

Headline features

• 18-35mm focal length (27-53mm equivalent)
• Extremely fast F1.8 maximum aperture
• Ring-type ultrasonic focus motor with full-time manual override
• Initially available in Canon EF, Nikon F and Sigma SA mounts

Sigma 18-35mm F1.8 DC HSM specifications

ที่มา : dpreview.com