About 8 months ago I purchased a new Sigma 50-500mm f/4.5-6.3 DG OS HSM APO lens (that’s a mouthful). I bought it during the final heydays of Microsoft ‘s Bing Cash Back program, when they were giving away cash on pretty much anything you could find in a search engine. Ah, the good ‘ol days. I never actually opened the box because at the time I wasn’t sure whether I’d be using Canon or Nikon for my long focal length shooting and have since decided on Canon for the long stuff.
I finally got around to listing the lens for sale on fredmiranda.com and found a willing buyer who only asked that I test the lens out first to make sure it doesn’t suffer from any Sigma-esce focusing problems. Smart move. I mounted the lens on my D7000 and did some IQ tests first. Images looked great – sharp at 500mm @ f/6.3, sharper still at f/8.0. Not a light speed demon by any means but for the price and focal range I consider the Sigma a good deal. Then I did my focus tests and uh oh, the lens started bucking like a donkey at 200mm. Either it would refuse to focus, meaning nothing happened when I pressed the back-button focus on my D7000, or the lens would do a few jerks to humor me and then just sit there like a sad, graphite-colored puppy. For the few times it actually attempted to focus it would take about a second to shift through its non-focal-distance-limiter-support range (in other words, no focal length limiter switch like on Canon/Nikon telephotos) and then give me that comforting focus confirmation “beep” on my D7000, only to be greeted by great bokeh that covered the entire range of frame, including the subject I was attempting to focus on. In other words, it was completely out of focus. Same results at 300mm and 400mm, but better at 500mm.
Needless to say the sale is off, at least until I get the lens fixed. To Sigma’s credit I looked up my serial number and it does fall within the range of recalled copies for the 50-500mm OS line, a recall that was proactively announced by Sigma all the way back in July 2010. So Sigma knows about the issues and got in front of the problem so it’s up to me to do my part and send the lens in for an AF motor tuneup. I’ll reevaluate the AF when it arrives back and post my results. In the meantime here’s a video showing the AF problems I observed.