jt354 wrote in post #16651124
I always thought focusing in AI servo then releasing would have the same effect as focusing in One-shot, with the added benefit of being able to keep the focus button held down to adjust focus if the subject starts moving. By using AI servo, I wouldn't have to re-press the button to change focus if the subject moves, but I also didn't think I lost anything by using servo on a stationary subject. Or is that what "AI Focus" is for?
Basically yes, using the Servo means you can AF, then let go of the AF button, to use it essentially as 1-shot AF. This is to avoid slight changes to focus if you see you have the focus you want, as opposed to keeping the button pressed, which means focus can keep changing slightly.
You can keep the button pressed, or re-press the button, to focus on the moving target.
If you got some back focused photos of a dog running or even walking towards you, that's completely normal. It is extremely rare to get 100% focused photos even for a walking dog and even with a much faster lens than this one. It's a relatively small aperture lens (more at the long end, which I assume you used?) and the AF, although not especially slow, is not very fast. This means a likely higher % of out of focus photos of moving targets than with a faster AF lens (e.g. the 300mm f/4 or f/2.8 primes).
In short a % (even a high %) of out of focus photos in this situation is normal.
I just thought of a couple of other possiblities.
If you used AF like you described before, with the back button and then letting go, then taking the photo...
Depending on camera, lens and maybe mode, the back button AF usually doesn't activate the VC. Maybe it's possible that by focusing, then activating VC ruins the focus? I have no idea and it's likely that ti doesn't, but maybe it's a possibility?
Another thing is (maybe more likely), the VC needs a (short) moment to work. If you AF using the shutter button then most of the time the VC is already working by the time the lens has focused, so no issue most of the time.
Maybe you are presing the shutter button to take the photo and the VC doesn't have enough time to work, causing the issue?
By the way I now see that I had to scroll and missed the squirl in the second photo. It is obvious that both focus and shutter/VC was good in that photo. The camera/lens can't automatically focus on the squirl through the more contrasty branches, so it chose them as the best contrast in the AF area and focused on them. If you used Servo it's possible that some of the time the focus was on the squirl.