« on: November 07, 2014, 01:55:40 AM »
I’ve been lurking here for quite a while and have been learning a great deal from these discussions. I have a few questions about autofocus speed and the relative importance of the lens versus the camera body. I shoot a 7D and I’m primarily using one of two lenses – a Canon 300mm f/4 L with or without a Canon 1.4X TC III or a Sigma 150 mm f/2.8 macro with or without a Sigma 1.4X TC. I shoot mostly wildlife, primarily birds, and macro, especially butterflies, dragonflies, and other smallish nature subjects. I shoot about 50% hand-held, about 50% monopod mounted and I almost always use the central autofocus spot on static subjects. My vision is not very good so I rely almost exclusively on the camera’s ability to autofocus my subject quickly and accurately.
Nothing wrong with relying on camera's AF. That is what it is for! And when shooting 10fps there is no way to rely on the eye to judge focus.
1. I have a sense (but no real measurements) that the addition of the TC to either lens slightly slows autofocus compared to the “naked” lens. Under identical shot conditions and lens/camera settings, is there a reason to expect that addition of the TC would slow autofocus lock? Maybe it is just my imagination?
Yes it does, Neuro has given you the math.
2. I’m thinking about upgrading to a 7DII next year. Will the new and improved autofocus system in the 7DII make a difference in improving the speed of autofocus acquisition with my current lenses? In other words, given identical shot conditions and camera/lens setting, will the 7DII be faster to autofocus than the 7D or is speed going to be limited by the lens system I have in use?
Faster maybe. How much faster? Very little. But overall it will be much better focusing device: Tracking, spread out better focus points etc.
3. I have heard it said that the image stabilization (IS) system actually slows down autofocus lock. One suggestion I have heard (or read somewhere) is to turn off IS when shooting birds-in-flight to allow the camera to lock focus more quickly. Is there any truth to this?
Don't think so. But even if it was, it would be so little that it does not matter.
All are unscientific personal thoughts.
Thanks for your help.