Problem with Autofocus in the EX1

[Dave Morrison]

On a related note, does anybody know where the autofocus detects these changes? I'm assuming that it is detecting changes inside the small center square but I'm not sure.

[Tom Roper]

You can observe the behavior of the auto focus by leaving peaking on. Set the color to red, level mid or high.

It's pretty understandable what it keys on, tilt the camera up or down a few degrees on your subject and observe the change. If it's locked down and the subject doesn't move, neither does the focus.

It also helps immensely to have detail ON. You can adjust the parameters of the detail setting to eliminate most of the concerns with it, namely the ugly EE halos. For example, for 60i turn the detail level to +10, the frequency to +50, the black limit to +50, and the white limit to -50. You'll struggle to see any halo-ing at all. For 24/25p, that's way too much sharpening however, turn the level down to -13 or whatever suits your preference. The salient point, is that contrast within the details is what the auto focus keys on. If you want to use auto focus, your opportunities are reduced when you turn detail off.

[Martin Drew]

Originally Posted by Tom Roper

...If it's locked down and the subject doesn't move, neither does the focus.

Thats not what I get with mine. I get constant hunting once focus is achieved. Its as if the AF is constantly moving to focus slightly either side of the current focus point to assess the sharpest focus. I know I am not alone because there was a lot of discussion on the subject in the early days. Are you sure yours stays rock solid in focus if you leave the AF switched on Tom?

Originally Posted by Tom Roper

...The salient point, is that contrast within the details is what the auto focus keys on. If you want to use auto focus, your opportunities are reduced when you turn detail off.

Again. Are you sure Tom, I haven't got my camera here to check but it would seem crazy to make AF effectiveness dependent upon the detail setting. Detail does affect the display of peaking however so if detail is off peaking is reduced and you don't see so much peaking when things are in focus, doesn't mean they aren't just as in focus though.

M

[Tom Roper]

Originally Posted by Martin Drew

Again. Are you sure Tom, I haven't got my camera here to check but it would seem crazy to make AF effectiveness dependent upon the detail setting. Detail does affect the display of peaking however so if detail is off peaking is reduced and you don't see so much peaking when things are in focus, doesn't mean they aren't just as in focus though.

M

That's a good point Martin. It would seem crazy to make AF effectiveness dependent on the detail setting. But then why make peaking dependent on it?

What I am sure of, is that I see the focus hunting stops after 2-3 seconds, on clear targets in front, with non-confusing uncluttered backgrounds. I know this because the distance/depth of field display stops moving, and the distribution of the peaking dots.

When you get back to your camera, will you try turning the detail on for a test? Interested in your finding. Again, I'm getting decent auto-focus performance, with detail at the above settings, std3 gamma.

[Martin Drew]

Originally Posted by Tom Roper

That's a good point Martin. It would seem crazy to make AF effectiveness dependent on the detail setting. But then why make peaking dependent on it?

The video signal displayed on the LCD is post processing, which is a plus because it means you can see the effect when you change the level of detail or gamma etc, etc. Peaking, Zebra, and other operational information is applied to that processed video signal for the LCD so they are affected by the processing previously applied. So it isn't ideal if you are using peaking as a focus assist for manual focusing, but it is understandable why it is done in this way. In contrast, I can't see any advantage to using a post processed signal for AF feedback, it would seem to make more sense to take that pre-processing and add any function specifically appropriate to improving AF effectiveness. That doesn't mean I am right of course, just seems odd to me. I will have to check on my camera when I get a second.

Originally Posted by Tom Roper

What I am sure of, is that I see the focus hunting stops after 2-3 seconds, on clear targets in front, with non-confusing uncluttered backgrounds. I know this because the distance/depth of field display stops moving.

Not for me. locked off camera, siemens star filling the entire frame and it still hunts. Not dramatically but very noticable if you are looking for it. It could be that some cameras are better than others. I hope that is that case, if it is I will get mine fixed.

M

[Martin Drew]

Originally Posted by Tom Roper

...When you get back to your camera, will you try turning the detail on for a test? Interested in your finding. Again, I'm getting decent auto-focus performance, with detail at the above settings, std3 gamma.

Will do

M

[Tom Roper]

I do agree with your logic Martin, except I don't understand why peaking should be displayed post processing. I do understand why Detail ON would be displayed post processing, but not peaking.

Peaking is a very functional focus aid, doesn't have any other purpose, and could be made even more functional if you didn't have to enable the Detail ON circuit to obtain the full benefit of the peaking. Why wouldn't the same level of peaking be displayed preprocessing?

It's that specific peculiarity that makes me question whether Detail ON is contributing to improved Autofocus behavior, or as you would say...not.