AF with oncoming subjects

Started Jan 7, 2013 | Questions thread
Anker BergSonne
Regular MemberPosts: 314Gear list
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Re: AF with oncoming subjects
In reply to Duncan C, Jan 7, 2013

Duncan C wrote:

Anker BergSonne wrote:

I think your expectations are too high. The AF is good, but huge changes in relative distance requires massive amounts of processing power that the processor just can't deliver. Possible also faster changes in focus than the AF motor can handle.

Anker

I have a couple of issues with your post. First, viewfinder based AF uses phase detection and a small number of focus points. The camera is not evaluating thousands of points of data. Just a few dozen. That shouldn't be beyond the capabilities of a modern processor.

Second, predictive autofocus is supposed to calculate speed and direction, and match it. The camera should be able to figure out that there is a subject approaching at a given velocity, and set the focus to track its motion as it comes in, while fine-tuning the focus change as it goes.

I don't know about limitations on the AF motor. I would think an AF-S lens would be able to track focus pretty darn quick however. That's a major point of the "ultrasonic" focus motors in these lenses. There's a lot less parts to move, so the focus is FAST.

I just realized that the OP wasn't using 3D tracking, so no wonder. In 3D tracking the focus system also uses color information so the processing load increases dramatically. As someone doing sensing and control for a living I can assure you that keeping track of moving objects isn't easy.

Anker

 Anker BergSonne's gear list:Anker BergSonne's gear list
Nikon D800 Nikon AF-S DX Nikkor 10-24mm f/3-5-4.5G ED Nikon AF-S Nikkor 70-200mm f/2.8G ED VR II Nikon AF Nikkor 50mm f/1.8D Nikon AF-S Micro-Nikkor 105mm f/2.8G IF-ED VR +3 more
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