The AFMA myth.

Started 5 months ago | Discussions thread
ThrillaMozilla Veteran Member • Posts: 4,322
Re: The AFMA myth.
1

poppyjk wrote:

Do you believe the OP is correct that AFMA changes only move the focus by a few millimeters rather than a few feet at 175 feet and 400mm?

I don't believe the OP made that point, although perhaps he could have stated it more clearly.

You are correct that large microfocus adjustments can easily exceed the depth of field, and one might even get the opposite impression from the original post.  I'll give you that, but I don't think that's the point of the discussion. You did, however, provide a good example of what he was talking about.

In your examples it's not clear whether the camera focused on the wall or the branch. Although it's likely that it's focused on the branch, you don't know that for sure. To make microadjustments, it's crucial to know exactly what the camera is focused on. Although you may have worked out a satisfactory procedure that works for you, I would still call this a procedural error.

The example the OP was commenting on showed an even larger ambiguity about the focusing procedure. In that example, if you look at the bubbles near the bottom of the frame, toward the left side, it appears that the focus is far in front of the whales. This points to a probable procedural error rather than an error that requires microfocus adjustments. His point is that in cases like that where there is confusion or there is probably a procedural error in focusing, which is very often the case, it doesn't make sense to start automatically with microfocus adjustments.

Incidentally, of your three examples the best focus was achieved with zero correction. This doesn't exactly make a compelling case for large adjustments.

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