Thread: Scanner Mode
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Old 21st August 2019
TonyR TonyR is offline
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Re: Scanner Mode

Scanner set to mode 3 can be a problem. It all depends what you want to happen if you can't keep the subject under the chosen focus points and if there is any other detail in picture to grab focus.

The scanner only comes into play if there is not enough detail in the image for the normal pdaf method to work. This can happen if the lens is completely out of focus or if the subject under the focus points has no detail, such as a blue sky. When the scanner runs, it racks the focus back and forth to try to get some detail to focus on.

So, in the case of tracking a bird against a clear sky, if I move the focus off the bird, the focus points can see no detail and the scanner may (probably depending on C-AF sensitivity) be invoked. This is the last thing that I want because racking the focus will make the bird go completely out of focus which means that I cannot recover tracking it.

So, I have my Scanner set to mode2, the idea being that it will invoke the scanner for the initial AF acquisition but not again if tracking is momentarily lost. However, this raises the question of what happens when the scanner is not run on the initial focus acquisition. WIll it run when I first lose track of the subject? I am not entirely sure.

Setting the scanner to mode 1 will ensure that the scanner will never be invoked. That will guarantee that the camera will not rack the focus when you lose the subject but it also means that you have to pre-focus, at least approximately, before every shot otherwise the camera may not be able to focus at all.

It is quite educational to set the scanner to mode 1 and see what the camera will and won't focus on. With my 300mm lens, it will really only fail to focus when shifting from a very close subject to a very distant one, or vice versa.

I think I may experiment again with Scanner set to mode 1 because I haven't tried it since firmware 3.0 came out. It may be with this firmware's increased preference for the closest subject, that mode 1 could work quite well.
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