X100 AF sometimes needs multiple tries

I should have explained further, what I meant is, there is nothing difficult about this shot, so you're quite right, it should have taken one attempt.

Jeff Charles said:

JonathanJK said:

Weird you're having this problem. It would seem something quite normal.

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I do not understand your post. Are you saying that needing multiple attempts to acquire focus is normal AF behavior? I've used a number of AF cameras, including several with contrast detection AF. All of them miss on occasion, but I haven't experienced the particular problem that I've described in this thread.
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Jeff

My cat, who likes to sprawl on my keyboard, is responsible for all typos, misspellings, factual errors, and faulty logic in my posts.

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http://jonathanjk.com/

Jeff,

Jeff, You seem to be saying that when DR is set to auto, the camera can change the ISO. I don't see any indication of this in my camera.
Jay

gava said:

Who knows what it will be trying to do there, the AF box is probably not all that accurate, and the algorithms may be working on too large an area and sometimes hitting the wrong exit point after a certain amount of time has expired, or too small an area not accurately reflected in the viewfinder and in this case have been trying to focus on the wall.

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I hadn't thought of that, but I've seen a number of reports about other cameras' focus boxes not corresponding exactly to the focus area displayed in the viewfinder.

The only pattern that I believe I've seen is that once the camera has focused successfully one time, it will continue to do so on subsequent tries. Since contrast detection AF works by "bracketing", i.e., overshooting and then undershooting focus until it gets it right, having the focus already at roughly the right distance would save time and prevent the AF from timing out.

gava said:

I expect that Fuji would be able to fix or improve this kind of performance issue in firmware if they were so inclined. They may or may not be so inclined.

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There's no way to know what Fuji will include in its firmware updates, but there are signs that they are taking the need for firmware fixes seriously. They have acknowledged dpreview's criticisms and they have requested suggestions from at least one other reviewer.

I'd guess that Fuji's engineers have a better understanding of the X100's AF performance than we do, and that they may already have improvements in the works that they were unable to complete in time for the initial release. We will find out soon enough.

gava said:

For myself I developed habits in the very early days (when AF was brand new to SLR cameras and not nearly as good as even the X100 is today) to automatically seek out good line contrast at a close distance to my AF point.

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I have that habit too. Actually, I thought I was doing that when I placed the focus rectangle on the meters, but I guess not.

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Jeff

My cat, who likes to sprawl on my keyboard, is responsible for all typos, misspellings, factual errors, and faulty logic in my posts.

jay Goldman said:

Jeff, You seem to be saying that when DR is set to auto, the camera can change the ISO. I don't see any indication of this in my camera.

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only if you set the ISO to Auto as well - it seems to put it a weird kind of "Dynamic Range Priority" mode ..

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A Problem is only the pessimistic way of looking at a challenge

Something which I forgot to mention in my earlier post is that Contrast Focusing relies on the camera being held steady as any movement will readily confuse any assessment of contrast as the contrast edges are blurred with movement. This applies particularly if any contrast detail is on the small side as would be the case in the given example.
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Keith-C

jay Goldman said:

Jeff, You seem to be saying that when DR is set to auto, the camera can change the ISO. I don't see any indication of this in my camera.

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Here is my understanding of how it works.

When DR is set to auto, the camera decides whether to use DR 100, 200, or 400, depending on how it analyses the scene. If it chooses DR 200, it sets ISO to 400. If it chooses DR 400, it sets ISO to 800. Of course, that only works with auto ISO. Even with auto ISO, if you set max ISO to 400, for example, DR 400 will be disabled, and cannot be chosen by auto DR.

What's interesting about this is that when DR 200 or 400 are selected, the X100 does not actually apply the gain implied by ISO 400 or 800 to the raw file. It exposes (aperture and shutter speed) as if the ISO is 400 or 800, but applies only ISO 200 gain. That preserves highlights, but leaves shadow areas too dark. The JPEG engine than boosts the shadows, presumably with an ISO 400 or 800 amount of gain.

This produces a surprising result with raw files. Brought into Lightroom, a DR 400 image will be two stops darker than one taken at DR 100 with the same aperture and shutter speed, and also at ISO 800.
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Jeff

My cat, who likes to sprawl on my keyboard, is responsible for all typos, misspellings, factual errors, and faulty logic in my posts.

KEITH-C said:

Something which I forgot to mention in my earlier post is that Contrast Focusing relies on the camera being held steady as any movement will readily confuse any assessment of contrast as the contrast edges are blurred with movement. This applies particularly if any contrast detail is on the small side as would be the case in the given example.

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Good point that I had not considered. Bracing is important, but with sufficient shutter speed, we can often get by with less than perfect technique. During focusing, of course, shutter speed does not come into play.
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Jeff

My cat, who likes to sprawl on my keyboard, is responsible for all typos, misspellings, factual errors, and faulty logic in my posts.