Thursday, April 7, 2011

F550EXR – Ultimate Low Light Video Focus Hunting Test — Review Part 18 ** Updated **

This is one seriously controversial topic. Does it hunt or doesn’t it? Can it focus well or not?

I had shot one video and it went very smoothly. At least, that’s how I felt about the result. No focus hunting, no serious misfocus, all in all it was decent. But then I tried to test 1080p and the results were totally different … blurry long end of the zoom, much more focus hunting … what was going on?

I thought about it and then realized that the resolution of individual details is much different between the two modes. And contrast detect is using differential contrast between these details to handle AF chores.

Hmmm … the F80 and F300 were both designed for 720p. We know that Fuji likes to reuse even their bad firmware ideas (e.g. selective noise reduction) ad nauseam … or at least until we force them to change it by complaining loud and long.

So it stands to reason, then, that the 720p algorithms were ported forward into the F550EXR … and the 1080p resolution suffers for it. What worked adequately in lower resolution does not in higher resolution.

Still with me? Well, I have proof.

I filmed a lamp in very low light and moved the zoom back and forth. The results were as follows:

  • At 1080p in center AF mode, focus at the long end always shifts off target, so it is never crisp unless you intervene by shooting an image at full zoom while filming; this causes the focus to be established in still mode and after that going back to full zoom reestablishes the correct focus – this is a serious bug in their firmware.
  • At 1080p in continuous AF mode, focus at full zoom hunts unmercifully. It is completely useless. This is a fatal bug in their firmware.
  • At 720p in center AF mode, there is a slight error at the long end again. It is less noticeable and some will tolerate it well. Shooting an image in still mode fixes things up as it did in 1808p.
  • At 720p in continuous AF mode, focus hunts with little flicks that are barely visible in a few pixels flickering, but it does not cause a lot of problems otherwise. It seems quite stable.
  • It appears that focus noise is  louder and more extended after focusing using a still image. So the trick comes with a penalty. I am not really surprised. Does anyone test these cameras before they leave the engineering department?

So the bottom line is that you can shoot videos using these methods:

  • 720p with continuous AF – seems pretty good and the video will follow the subject, keeping it in focus … there will be some hunting I’m sure.
  • 720p or 1080p with center AF – start the video, zoom to 360mm, snap an image … after that you will be able to zoom out and the subject will snap into crisp focus. If the subject moves and goes out of focus, you can flick the zoom lever to force a refocus. Or shoot an image at the cost of an interruption in the video.

So not perfect choices, but not bad. Most people are probably out there shooting in 1080p with continuous focus and not realizing that this feature is fatally wounded.

The following video demonstrates all of these features and the trick of preshooting an image. Enjoy.

More caveats:

  • EXR AUTO mode interacts with the video modes in that even center focus hunts. This because EXR AUTO sets continuous AF and that obvious overrides what you set in the video AF mode. Another firmware bug.
  • The HS20 guys say that advanced anti blur also interacts, causing problems for center focus getting focus in the first place. I found that it seems to go far out of focus even in 720p mode when using this setting.
  • The trick of establishing perfect focus by shooting a still also seems to eliminate focus hunting in 720p and continuous AF mode. Nothing visual anyway. Even rocking the cam back and forth does not stimulate it once it locks. 1080p still shunts though. *sigh*

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