What you are describing sounds like the behaviour of a very accurate focusing system being provided acute data. I suspect that the lens has such excellent resolution and contrast wide open that the camera's AF system is able to tune into even subtle changes, hence the "jerky" zip-zip-zip that you describe. The fact that this occurred in good light and not in poor light supports this theory.
Maybe the 85L doesn't provide the AF system with as much visual data. That combined with the 85L's pedestrian AF speed and the "softer" functioning of Canon USM over Sigma HSM makes for a comparatively "jerky" experience with the Sigma.
Either way, I can't imagine seeing this as a huge drawback, especially since the lens costs less than half as much money as the 85L.
okafoja wrote:
Can someone please explain to me what lens jerking is? English is my second language. I never heard anyone use that word to describe a lens. Is this something to ask when buying a used lens.
If I'm not mistaken, I think there are several "shops" near B&H in NYC that provide services to correct that problem. Maybe that's why B&H sells so many lenses.
My 85mm 1.4 arrived last Tuesday. I did some tests at 1.4 of my daughter light by a 60w lamp and each time it focussed immediatly - better than my 85l. On Saturday I shot 12 Family portrait - over 800 pics and 50% with the 85 ( the rest with the Sig 50 f1.4) and evey one is spot on - not a single duff shot.
I the real world of taking photos, this lens is just superb
What you are describing sounds like the behaviour of a very accurate focusing system being provided acute data
For what it's worth, I've observed this behavior with my Sigma 85 on my Nikon D700. My gut feeling was that your explanation was indeed the case. It only happened when the subject was relatively close, and I think I could probably attribute it to the camera trying to decide which eyelash to focus on, or cycling between focusing on eyelashes or eyeballs.
