i just found out that this sigma lens does not allow AF-C with viltrox speedbooster EF-M2 II. It just stops at one shot and not even in focus. AF-S works fine and accurate.

Focus is silent, and you may grab the ring at any time for instant manual focus override. At least on the Nikon version I tried, Sigma finally has this figured out.The above image was captured at 18mm, f/1.8 using a Canon EOS 60D at a not-kind-for-faces close focus distance. Flare slowly increases as the aperture narrows until becoming noticeable at f/8 and by f/16, strong flaring is obvious. Since 1982, PCMag has tested and rated thousands of products to help you make better buying decisions. See how we test.

In the past, Sigma have carved a niche for themselves creating new, exciting optics that don't already exist in manufacturer's own lens line-ups, such as their 15-30mm& 12-24mm lenses for full frame cameras, that were the first of their kind. Featuring Sigma's HSM (Hypersonic Motor) driven AF, the Sigma 18-35mm f/1.8 DC HSM Art Lens focuses with very good speed. As an off-brand lens it has unproven (with me) service facilities, and unknown future parts availability. When the HSM motor dies, you're dead unless you can get a replacement part. Nikon 35mm f/1.8 DX for a fraction of the price. On Canon, the classic professional Canon 35mm f/1.4 L is a steal today, and a much better long-term investment than this consumer zoom. Finally, at 35mm there is a slight further reduction in overall sharpness, although clarity is still very good across the frame at maximum aperture. Peak sharpness across the frame is achieved between f/4 and f/5.6 for this focal length.

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What this means is that while the 18-35mm has truly superb glass, autofocus problems mean that it can be difficult to get the full benefit when shooting at large apertures, which somewhat negates the lens's key selling point. Not every wide-open shot will be misfocused by any means, and you'll still get prime-like image quality when shooting stopped-down. But unfortunately, the fact that you can't rely on always getting correct focus makes the lens a bit less easy to recommend over an F2.8 zoom in the 17-50mm class. Specifically for APS-C, I'd also buy the thoroughly professional Nikon 17-55mm f/2.8 or Canon 17-55mm f/2.8 IS long before I bought this Sigma lens - but that's just me. I'm the kind of guy who still takes my 12-year old used car to the original new-car dealer for service, because I like to keep everything original and authentic, not mixing off-brand parts on my nice car. On my Nikon D7100, AF was dead-on for every frame, especially shot at f/1.8 where this is critical. Additionally, the Sigma’s “35mm equivalent” focal length range of 27-53mm is standard and well-suited for most video work. Usually this APS-C to full-frame focal length conversion doesn’t work in your favor, but this one does. Cropped, high-quality 4K The Sigma 18-35mm f/1.8 is bulky, long, and weighs nearly two pounds (1 pound, 15 oz to be exact). This makes the lens somewhat cumbersome and heavy when shooting handheld on the R5. Requires an adapter

When asked if the limited focal length range design was necessary to keep the lens size manageable and the cost affordable, Sigma responded: Aspherical. Look at the reflections from the front element and you'll see just how wildly aspherical it is.

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This is an amazingly sharp lens, even wide open at ƒ/1.8, which is typically not the case with very wide-aperture lenses. At 18mm and ƒ/1.8, the Sigma shows very little corner softness and a good portion of the center and middle of the frame are very sharp indeed. As we've seen time and again, very wide-aperture lenses (> ƒ/2.8) can often show significant corner softness when used at their widest apertures, but the Sigma 18-35 not one of them. In this respect, it beats even many fast prime lenses in its focal length range. Our used products are subject to wear and tear in comparison to brand new products. This also applies to accessories that are supplied with the camera including batteries which may have a lower optimum performance level/life expectancy.

The perspective required for tight 18-35mm portraits make this lens a bad choice for such – unless you want to get "artistic".

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The Sigma 18-35 has an attractive, clean, slender, smooth design that, if I haven't made it clear already, I like a lot. and what does "Contemporary" mean for a lens designation? Will it still be contemporary in 10 years? Are the "A" and "S" lenses not just as contemporary?). The 18-35mm focal length is rather wide angle for most sports needs, but this lens certainly can be used for the narrow niche of athletic activities these focal length work for. While this lens is designed to cover only an APS-C-sized camera sensor, this lens mounts and functions on a full frame DSLR. The rear of this modestly-sized hood has a rubberized surface that makes it easy to grasp for bayonet installation/removal.