Autofocus Behaviour

[Alex Leith]

Originally Posted by Greg Boston

Not being able to focus while zooming on the XL1, XL2, XLH1, and these new cameras is the result of having only a single motor that does double duty. You can't focus and zoom at the same time even if you're in manual mode. So that isn't actually a problem.

But the problem happens when the camera and target are both static. Zoom in, let the camera get focus, zoom out and in again, and the camera is out of focus. If it happened in MF as well I'd say it was a back focus problem, but in MF focus holds.

In AF the whole image pulses in and out of focus as you zoom in or out - especially on the long end of the lens.

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Edit: Oh wait, read the post, Alex!... Your comments were about the XL1, XL2 and H1... (not the A1)

[Brad Tyrrell]

Originally Posted by Greg Boston

You could send your XL1 lens in to Canon and they can set it. Don't know how much it will cost though.
-gb-

Actually, I've had it in a couple of times, first on warranty then for cash, - didn't help. Blown a pixel finally so I've got to replace it. Fixing blown pixels in post in addition to covering out-of-focus zooms gets to be a real drag.

Before the XL-1 I had an old Panasonic 2 chipper designed for svhs. Zoom was powered, but everything else was manual. Could do just what I wanted. (Of course looking at old svhs tapes, I can't believe how bad that resolution was, - good grief!)

[Alex Leith]

Here's a quick clip of the pulsing in action. It's fairly low light in this clip, but exactly the same happens in normal light too.

You can see as I zoom in the background pulses in and out of focus.

[Richard Hunter]

Hi Alex. I saw a demo of the A1 here in Singapore on Thursday evening, and noticed that the autofocus was hunting quite a bit when the sales guy was moving things around. The lighting was very dull so this wasn't really unexpected, but it does seem to mean that we'll still need to use manual focus when we need reliability. Looks to me like the new focus system is not enough of an improvement for shooting in low light conditions.

Om a more positive note, I thought the image from the camera was fabulous, the colours had a very nice richness to them, even though the lighting was poor.

Richard

[Holly Rognan]

That was hunting! I have had mine hunt a little, but not that bad. I like to use manual when possible, but the instant autofocus shouldn't be doing that.

I don't know what to tell you.

[Tom Roper]

That's wicked bad. What were your other settings, aperture, shutter etc.?

[Alex Leith]

It seems to "hunt" whenever you operate the zoom. It's like the zoom is somehow interfering with the IAF. At the start of the shot where I'm not zooming the focus is solid. But as the zoom creeps forward I can feel the AF shunting.

25F; 1/50th; Aperture as wide open as it will go. 6dB of gain in this case ('cause it was dark) but it did the same with 0dB and -3dB of gain during the day.

I'm going to speak to the dealer and get it changed on Monday.

[Poppe Johansson]

I'm able to reproduce exactly that kind of hunting (PAL A1), but only when there's very dim light and objects are dark colour. Even then it's quite hard to get focus to hunt, but I have seen this couple of times.
But it really shouldn't appear in normal light. So I quess this isn't normal.

[Tom Roper]

I did a slow zoom from a 5-6 feet of an object on the carpet in very dim light with IAF on starting at 1/60 F1.6 (the aperture opens up as I zoom), 12db gain and I could not get it to hunt.

It almost seemed like your cam couldn't decide whether to focus on the black bag or the angled floor slats behind, and dithered between them, a behavior consistent with two possibilities:

1.) IAF was not on or not working
2.) The minimum focusing distance increases as it zooms toward the telephoto end, making a lock more difficult.

Either way, it is severe and dithers much worse than I have observed under any condition. I would return the cam for replacement or service.

[Tony Tremble]

It's till not possible to develop an idiot proof camera then?

Read page 36 of the manual. That camera-focus clips has ALL the features required to throw the auto focus off.

I am amazed that you would expect better! A dark featureless blob on featureless background under poor lighting is probably something the Canon engineers hadn't planned for...

If you must record something like that first zoom in, focus up with either manual or temp AF, zoom out. Then record your zoom making sure that the camera is not in AF beforehand.

To rely on auto focus during a zoom in is an amateurish technique doomed to failure and does not reflect on the camera but the person using it.

Sorry to be blunt but the XH-A1 is a wonderful piece of kit in the right hands.

TT

[Tom Roper]

Sorry Tony but I think the issue is something wrong with his cam. The discussion of shooting style, subject matter is not germaine to the auto focus problem. Alex has stated the cam does this in quite a few situations, presumably even the ones not limited to page 36 of the manual.

But be glad, the Canon Zoom lens is a Parfocal (...if it is...), because if not, the focus plane will change with zoom length as it does on many DSLR lenses, in which case a technique of zooming in to lock manual focus before zooming back out will result in an out of focus image.

[Brad Tyrrell]

Originally Posted by Tom Roper

But be glad, the Canon Zoom lens is a Parafocal (...if it is...), because if not, the focus plane will change with zoom length as it does on many DSLR lenses, in which case a technique of zooming in to lock manual focus before zooming back out will result in an out of focus image.

IF IT IS ???? Could someone PLEASE say more about this? Please? Please?

[Chris Hurd]

Originally Posted by Tom Roper

The discussion of shooting style, subject matter is not germaine to the auto focus problem.

Completely disagree. Actually it has everything to do with it. As Tony pointed out above, there are certain situations in which AF cannot be expected to function properly. These include shooting toward reflective surfaces, subjects with low contrast or without vertical lines, fast moving subjects, shooting through dirty or wet windows, and night scenes. "Additionally, in 30F and 24F mode, autofocus takes longer than in the 60i mode. When recording under dark conditions, the focusing range narrows and the picture may appear blurred. Autofocus may not work well on the following subjects. In that case, focus manually." All of this is verbatim from the operator's manual.

This goes beyond just the simple understanding that AF needs contrast (and therefore light) in order to work properly. There are bright-light situations that can confuse AF as well.

As far as hunting during a zoom, that won't happen if critical focus is established first.

Yes I think Alex should absolutely go ahead and have his camera checked out by Canon UK's service department. I would be very interested to know the results. Nothing is going to be properly diagnosed on an internet message board. All we're capable of doing here is to give Alex the best possible advice, which is, get the camera checked by Canon service.

[Tony Tremble]

Originally Posted by Tom Roper

Sorry Tony but I think the issue is something wrong with his cam. The discussion of shooting style, subject matter is not germaine to the auto focus problem. Alex has stated the cam does this in quite a few situations, presumably even the ones not limited to page 36 of the manual.

But be glad, the Canon Zoom lens is a Parafocal (...if it is...), because if not, the focus plane will change with zoom length as it does on many DSLR lenses, in which case a technique of zooming in to lock manual focus before zooming back out will result in an out of focus image.

I think you mean Parfocal. ;) If it's not parfocal then it's useless.

Having seen the clip I don't think it is symptomatic of a camera problem. If there are well lit situations where a subject should be AFed without a problem then let's see it. I don't think the clip shows anything that wouldn't be expected of many cameras.

[Tom Roper]

Originally Posted by Chris Hurd

As Tony pointed out above, there are certain situations in which AF cannot be expected to function properly.

Chris, I'm just saying I shot that same thing to test and didn't remotely get that herky jerky jumping jack autofocus hunting problem. Try duplicating it and see if you do.