SAF Front Focus and CAF/SAF Focus Comparisons with the 300mm f4 – E-M1s.

Started 3 months ago | Discussions thread
OP drj3 Forum Pro • Posts: 10,939
Re: SAF Front Focus and CAF/SAF Focus Comparisons with the 300mm f4 – E-M1s.

Gary from Seattle wrote:

I have noticed that with 840mm on the EM-1X that with distant birds there is a tendency to front focus; though not uniformly so. This on water birds, so with texture in the water it is fairly easy to see where exactly the camera focused. The error is large enough to render some images useless. However, I also need to factor in the fact that I am probably moving the camera some in a burst sequence. Also, I may at times be shooting when the green box is no longer green - on focus.

With CAF, the cameras first focus and then confirm focus. The delay is significant only when the target is moving.

With stationary targets I wait for the focus confirmation, with moving targets, I ignore the green box.

It is important to wait on the focus confirmation if you have AF Focus Adjusted the lens. The correction will not be applied until focus is confirmed.

At least 80% of my flying swallow images will not have focus confirmation, even with a fairly long sequence of images which are in focus.

When the eye of a bird is large enough for AI to lock in on the eye, the camera tends to do much better.

With the numbers you have here and a telephoto lens, the indication is that a slightly greater aperture is likely to keep the focus within DOF. Also the DOF may well be such that it is very narrow anyways, and for instance it makes a difference whether or not the bird turns it's head.

The front focus will generally be noticed by the area in focus, more than the sharpness at the focus point.  It is important when you are trying to get the best feather detail for closer targets or want to balance focus on your target.  With more distant targets with a greater DOF and less detail, it would be far less important.

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