... I think the purpose of servo is seriously misunderstood.
i am insteresting in your understanding about ai servo. as if you would like to share, i am your audiance...
note: i am using both (with dof button re-config), depending on cases
Ok, so let me start by saying that in my world of candids (i.e. weddings) unless the eye closest to the camera is critically sharp, the picture goes to the virtual trash can. Even a slight focus error (say I focused on the eyeglass frames) is completely unacceptable. In fact, nothing short of tack sharp eye(s) can be passed on to the client.
Second thing that needs mentioning is that I shoot wide open with fast primes. So f/1.4 is where I live.
With that being said, servo could never do for me what I do manually with single shot:
- Servo is reactive, not proactive. It doesn't know where your subject is GOING TO BE, it can only tell where the subject moved after it already happened. Once subject moves out of focus, servo is catching up. This is especially a problem when the subject is moving straight towards or away from you.
- Servo can't predict people's reactions. I can tell by the body language whether a person is going to lean forward or backwards once they start laughing at the incredibly hilarious joke they just heard from a person they were chatting with.
- Servo doesn't understand that focus needs to be on the eye of the subject or the picture is useless. To ensure that I get the eye in focus, I use single focus point only. I dont want the camera making a mistake. Unfortunately you can't use servo with a single focus point only :-)
- With candids, timing is everything. So I want to take a picture exactly when the time is right, not when servo catches up to the subject. So it is much faster for me to wait it out and focus in the split second when the moment is right, than to let servo chase the subject around and be completely in the wrong place when I need to take the picture.
But I'm not saying that servo is useless, don't get me wrong. In other types of photography where subjects that are moving really fast and failure rate is really high (flying birds, fast action sports etc) servo can be of tremendous value. I can't imagine shooing a soccer game without it (unless I'm shooting the goalie only :-)). Continuous fast action requires a completely different approach to photography, especially if you don't know what that "right moment" will be.