CarpeyBiggs
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 p.1 #19 · example of 40D focus drift in AI Servo. | |
Alan321 wrote:
firstly, the same thing happens with moving subjects too (people at walking pace at about 60m range).
Hi Alan, interesting post here, but I think your test is misleading you, and your camera is probably fine. It's kind of like driving a ferrari on the go-kart track. AI-Servo isn't designed for still, non-moving objects.
Alan321 wrote:
Secondly, what if we want to focus on something close-ish such as a wildflower without using a tripod ? Your own movement can upset the focus unless you use AI Servo mode.
Hmm... Solution? Use a tripod. If not possible, stop down and take a few images with your natural "sway," and hope one of them nails it. Again, this is not movement that AI-Servo is designed to predict. You natural body sway is somewhat random and difficult to predict, especially for the 40D's algorithms. The AI-Servo is designed to track subjects that are moving in predictable patterns. Once the pattern is disrupted, it has to regain it's focus points and predictions again.
Alan321 wrote:
Or, what if we want to shoot a bird that may take flight ? Are we supposed to change modes as it takes off and still get the action, or do we use AI Servo all along ? One Shot will trash the flight shots. AI Focus will take too long thinking about it and trash several before it switches over.
You use AI Servo here, but when the bird isn't moving, you stop using the focus. I use CF 4-3, where focus is moved to the * button. When the bird is still, I focus once, then stop focusing, otherwise the camera thinks I am telling it that the bird is moving, when in fact it isn't. The result will be focus hunting. If the bird takes off, engage the focus again as it starts moving, so the focus can track it.
Alan321 wrote:
What I am doing is not invalid or unreasonable, and so yes it is Canon's fault. My problem, but their fault.
I guess if you feel it is Canon's fault, you might want to try a different brand. But my feeling is that it is a technique issue, probably not a camera issue. Who knows though, I could be wrong.
Alan321 wrote:
The fact that AI Servo applies predictive focus does not preclude it from working with a stationary subject, and does not account for it taking several shots to get back on track. This is not first generation AI Servo, you know, and it should not behave like it is.
See above explanation.
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