Click to Enlarge In testing the lens under good sunlit conditions and on scenes with good contrast, we found the focus to be surprisingly fast for such a big lens. But the AF was sluggish when encountering scenes lacking dramatic contrast. Thankfully, you can easily take control of focusing with the always-on manual focusing ring option.
Strangely, there is no focus limiter, which would help to speed AF when it searches if engaged. Such a limiter would be a nice touch on a lens that focuses from 20 feet to 200 feet before infinity. I was trying to track turkey vultures against a solid blue sky, and on more than a few occasions, the Sigmonster would search all the way through these 180 focusing feet before I disengaged AF and manual focused to very close to the subject distance before re-engaging AF.
It is a challenge to shoot with such a long lens. As the focal length increases, you'll want a faster shutter speed to minimize image blur due to camera and lens movement and vibration, which is amplified at longer focal lengths. With such a narrow field of view, tracking moving subjects can be tough. Fully zoomed to 800mm, on an APS-C sensor camera, such as the Canon EOS 20D, you're dealing with just under 2º angle of view at an effective focal length of 1280mm, so you've got very little wiggle room when tracking.
Due to the slow maximum aperture of f/5.6, this lens presents challenges in low-light. It is what I call a “mostly sunny” telephoto lens. You’d be over-lensed and under-f/stopped at many night sporting events, but for daylight sports, it could be useful to pull in distant action on a ski jump, racecourse, or to zoom in on a batter from over the center field wall.
Wildlife shooters will love the reach of the Sigmonster, too. It is not just about making a shot of a distant animal on the Serengeti. The short minimal focal distance also allows you to capture amazing detail of small animals, without invading their comfort zone. I would not have been able to make the tight photo of a juvenile rabbit blissfully unaware of the camera with a shorter lens from the same distance, given the same frame coverage and detail.
My overall impressions after a couple of days with the Sigmonster? It’s huge, heavy, and has its quirks, but the impressive optics and solid construction outweigh any negatives.
When I do take that trip to the Serengeti I’ve been dreaming of, I’d love to have the Sigmonster in my arsenal.
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