Autofocus Behaviour at DVinfo.net

Alex Leith · December 2nd, 2006, 07:01 AM

Can I just check how the autofocus is for other people?

I get a lot of pulsing even with a static camera aiming at a fairly easy target (without any obstructions). And when shifting the camera onto a different object the focus often shunts ALL the way to the near-focus(?) end before focusing back out to where it should be.

When it does operate normally the IAF usually throws it too far, and the AF has to back it up a bit (which looks fairly ugly and makes it unusable in-vision). And then sometimes it it just sits there doing nothing for a few seconds and takes up to 8 seconds to get focus.

Now I normally work with AF off (of course) but pressing the AF button can take up to 8 seconds to get a lock makes it fairly useless.

I'm guessing this isn't usual behaviour...?

Greg Boston · December 2nd, 2006, 07:17 AM

What frame rate are you shooting in? I can't say for sure on the new XH cameras because they have the hybrid AF system. However, on the XL2 and the XLH1, the image on the CCD block is what AF uses and is not very good when the camera is at 30P or 24P because the CCD block gets clocked at slower rates and doesn't get enough motion sampling updates to autofocus reliably.

Also, the CCD based autofocus wants good light and scenes which have some vertical objects with decent contrast (which goes back to the ample light thing).

Just some food for thought, maybe it will help.

-gb-

Brad Tyrrell · December 2nd, 2006, 07:23 AM

Somebody say it ain't so.

I'm just about to FINALLY upgrade from my old XL1 with its built-in focus problems. In the posts I've read so far, folks seem to like the focus so I thought the A1 was for me, but ....

John Huling · December 2nd, 2006, 07:33 AM

My Auto focus worked on a hand held studio shot with only 2 25 watt lamps on. I don't know if that's good but it worked for me
John

Alex Leith · December 2nd, 2006, 07:35 AM

Quote:

Originally Posted by Greg Boston

What frame rate are you shooting in? I can't say for sure on the new XH cameras because they have the hybrid AF system. However, on the XL2 and the XLH1, the image on the CCD block is what AF uses and is not very good when the camera is at 30P or 24P because the CCD block gets clocked at slower rates and doesn't get enough motion sampling updates to autofocus reliably.

Thanks Greg, I'm shooting 25F, but as I understood it the point of the IAF was to get into the right ball-park with the focus so you weren't waiting for the CCD.

The thing that worries me is the fact that sometimes the focus shunts all the way to one end and then back again, and other times the IAF just sits there doing nothing. 8 seconds is a hell of a long time for ANY autofocus system to wait to get a lock.

I was testing this in the house (fairly bright, daytime), but I think I'm going to go and find out what it's like outside.

Alex Leith · December 2nd, 2006, 08:35 AM

A bit of a play outside seems about the same. Sometimes the Instant Auto Focus seems to work and sometimes it sits there doing nothing or focuses in totally the wrong direction before getting it right.

Performance is similar with Normal Auto Focus turned on, except slower to find a lock.

Also, it won't hold focus through the zoom range, flicking in and out of focus through the zoom, especially on a faster zoom setting. This was tested by focussing on a nice contrasty poster on the wall of a well lit room about 4m/12ft away (without any foreground obstructions). I allowed the camera to focus, zoomed halfway out, paused, and then zoomed back in again. Through the range it repeatedly gets sort of "kicked" out of focus, then refocuses. By the time you get back zoomed in, the poster is out of focus and takes a moment to get focus back.

Has anyone else experienced this?

Brad Tyrrell · December 2nd, 2006, 09:13 AM

"Also, it won't hold focus through the zoom range, flicking in and out of focus through the zoom, especially on a faster zoom setting. This was tested by focussing on a nice contrasty poster on the wall of a well lit room about 4m/12ft away (without any foreground obstructions). I allowed the camera to focus, zoomed halfway out, paused, and then zoomed back in again. Through the range it repeatedly gets sort of "kicked" out of focus, then refocuses. By the time you get back zoomed in, the poster is out of focus and takes a moment to get focus back."

Aaaggghh. This is what the XL1 does. Please tell me this was fixed on the XH-A1 and that we're hearing about one that needs to be returned to the shop.

Cody Lucido · December 2nd, 2006, 09:14 AM

I have not experienced the issue you are describing. My A1 gets focus almost instant and keeps it. You might have a lemon.

Alex Leith · December 2nd, 2006, 09:19 AM

Thanks Cody, that's what I wanted to hear (I didn't fancy trying to work with this).

I suspect the root cause of the matter is something to do some sort of automatic back-focus adjustment - although that wouldn't explain why it holds focus in MF...

Time to get it swapped out! And to think, I spent 3 hour sitting in a traffic jam picking this one up on Friday!

Tom Roper · December 2nd, 2006, 09:42 AM

I know what is being described as "pulsing" is. I have seen it, but the phenomena only happened for me in very dim light. It happened, but I can't just reproduce it at will. As for the failure to lock focus onto an object I have seen that too, but again was a consequence of very dim lighting, or strong backlighting through a window, etc.

Alex, in my use the focus has been robust and reliable, with no negative behavior whatsoever in strong light, and very excellent in dim light. I am not able to induce hunting at will, although I have seen it happen once or twice.

In totality, makes me think yours should be inspected by Canon.

Do you have a filter in front of the lens?

Alex Leith · December 2nd, 2006, 10:38 AM

Thanks Tom,

No filter in front of the lens. I was testing in both indoor daylight (well exposed at about F4), and outdoor (again plenty bright enough), so I don't think it's a low light issue.

I wouldn't mind hunting occassionally, but every fourth focus this one seems to shunt totally to the wrong end of the focus range and then back again, or it just sits there doing nothing at all.

And the pulsing is pretty contstant, especially whilst zooming.

Oliver Horn · December 2nd, 2006, 12:31 PM

Hi. My A1 seems, er A1! No focus issues. In fact it seems better than my XL2 with stock lens. Trot back to the dealer quick and compare it to another unit.
Regards,
Oliver Horn.

Greg Boston · December 2nd, 2006, 12:46 PM

Quote:

Originally Posted by Brad Tyrrell

"Also, it won't hold focus through the zoom range, flicking in and out of focus through the zoom, especially on a faster zoom setting. This was tested by focussing on a nice contrasty poster on the wall of a well lit room about 4m/12ft away (without any foreground obstructions). I allowed the camera to focus, zoomed halfway out, paused, and then zoomed back in again. Through the range it repeatedly gets sort of "kicked" out of focus, then refocuses. By the time you get back zoomed in, the poster is out of focus and takes a moment to get focus back."

Aaaggghh. This is what the XL1 does. Please tell me this was fixed on the XH-A1 and that we're hearing about one that needs to be returned to the shop.

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.

If you are not trying to zoom and just moving the camera around, the focus should track. If it doesn't, you've got a problem.

-gb-

Brad Tyrrell · December 2nd, 2006, 01:14 PM

Quote:

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.
-gb-

Yipes, I didn't realize that! I'm pouting big time. It is actually a problem for me.

I shoot events and need to pan & zoom constantly, sometimes quickly sometimes slowly. Will the XH-A1 hold focus through a zoom on the same subject? Can I put focus or zoom in a fixed or manual mode and change the other?

My XL-1 won't hold focus through a zoom no matter what! It requires extensive post to cover.

Are there any new HDV cameras that can do what I want?

(Putting credit card away)

Greg Boston · December 2nd, 2006, 01:22 PM

Quote:

Originally Posted by Brad Tyrrell

My XL-1 won't hold focus through a zoom no matter what!

You have a back focus or 'flange back' adjustment issue. On the XL1, XL2, these are not user level adjustments. The XLH1 has both manual and auto back focus adjustments. I believe the new XH series have auto FB adjustment only because it's a non removable lens.

Higher end lenses and the old Canon manual 14X and 16X have external manual adjustments.

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

-gb-

December 2nd, 2006, 07:01 AM	#1
Alex Leith Major Player Join Date: Mar 2005 Location: Northampton, England Posts: 500	Autofocus Behaviour Can I just check how the autofocus is for other people? I get a lot of pulsing even with a static camera aiming at a fairly easy target (without any obstructions). And when shifting the camera onto a different object the focus often shunts ALL the way to the near-focus(?) end before focusing back out to where it should be. When it does operate normally the IAF usually throws it too far, and the AF has to back it up a bit (which looks fairly ugly and makes it unusable in-vision). And then sometimes it it just sits there doing nothing for a few seconds and takes up to 8 seconds to get focus. Now I normally work with AF off (of course) but pressing the AF button can take up to 8 seconds to get a lock makes it fairly useless. I'm guessing this isn't usual behaviour...? __________________ Alex

December 2nd, 2006, 07:33 AM	#4
John Huling Regular Crew Join Date: Nov 2006 Location: USA Posts: 172	My auto focus works fine My Auto focus worked on a hand held studio shot with only 2 25 watt lamps on. I don't know if that's good but it worked for me John

December 2nd, 2006, 08:35 AM	#6
Alex Leith Major Player Join Date: Mar 2005 Location: Northampton, England Posts: 500	A bit of a play outside seems about the same. Sometimes the Instant Auto Focus seems to work and sometimes it sits there doing nothing or focuses in totally the wrong direction before getting it right. Performance is similar with Normal Auto Focus turned on, except slower to find a lock. Also, it won't hold focus through the zoom range, flicking in and out of focus through the zoom, especially on a faster zoom setting. This was tested by focussing on a nice contrasty poster on the wall of a well lit room about 4m/12ft away (without any foreground obstructions). I allowed the camera to focus, zoomed halfway out, paused, and then zoomed back in again. Through the range it repeatedly gets sort of "kicked" out of focus, then refocuses. By the time you get back zoomed in, the poster is out of focus and takes a moment to get focus back. Has anyone else experienced this? __________________ Alex

December 2nd, 2006, 09:14 AM	#8
Cody Lucido Major Player Join Date: Sep 2006 Location: Seattle, WA Posts: 206	I have not experienced the issue you are describing. My A1 gets focus almost instant and keeps it. You might have a lemon. __________________ www.CodemanStudios.com

December 2nd, 2006, 09:19 AM	#9
Alex Leith Major Player Join Date: Mar 2005 Location: Northampton, England Posts: 500	Thanks Cody, that's what I wanted to hear (I didn't fancy trying to work with this). I suspect the root cause of the matter is something to do some sort of automatic back-focus adjustment - although that wouldn't explain why it holds focus in MF... Time to get it swapped out! And to think, I spent 3 hour sitting in a traffic jam picking this one up on Friday! __________________ Alex

December 2nd, 2006, 07:17 AM	#2
Greg Boston Wrangler Join Date: Oct 2003 Location: DFW area, TX Posts: 6,117 Images: 1	What frame rate are you shooting in? I can't say for sure on the new XH cameras because they have the hybrid AF system. However, on the XL2 and the XLH1, the image on the CCD block is what AF uses and is not very good when the camera is at 30P or 24P because the CCD block gets clocked at slower rates and doesn't get enough motion sampling updates to autofocus reliably. Also, the CCD based autofocus wants good light and scenes which have some vertical objects with decent contrast (which goes back to the ample light thing). Just some food for thought, maybe it will help. -gb-

December 2nd, 2006, 07:23 AM	#3
Brad Tyrrell Major Player Join Date: Oct 2003 Location: Morristown, New Jersey Posts: 249	Somebody say it ain't so. I'm just about to FINALLY upgrade from my old XL1 with its built-in focus problems. In the posts I've read so far, folks seem to like the focus so I thought the A1 was for me, but ....

December 2nd, 2006, 09:13 AM	#7
Brad Tyrrell Major Player Join Date: Oct 2003 Location: Morristown, New Jersey Posts: 249	"Also, it won't hold focus through the zoom range, flicking in and out of focus through the zoom, especially on a faster zoom setting. This was tested by focussing on a nice contrasty poster on the wall of a well lit room about 4m/12ft away (without any foreground obstructions). I allowed the camera to focus, zoomed halfway out, paused, and then zoomed back in again. Through the range it repeatedly gets sort of "kicked" out of focus, then refocuses. By the time you get back zoomed in, the poster is out of focus and takes a moment to get focus back." Aaaggghh. This is what the XL1 does. Please tell me this was fixed on the XH-A1 and that we're hearing about one that needs to be returned to the shop.

December 2nd, 2006, 09:42 AM	#10
Tom Roper Trustee Join Date: Jun 2004 Location: Denver, Colorado Posts: 1,891	I know what is being described as "pulsing" is. I have seen it, but the phenomena only happened for me in very dim light. It happened, but I can't just reproduce it at will. As for the failure to lock focus onto an object I have seen that too, but again was a consequence of very dim lighting, or strong backlighting through a window, etc. Alex, in my use the focus has been robust and reliable, with no negative behavior whatsoever in strong light, and very excellent in dim light. I am not able to induce hunting at will, although I have seen it happen once or twice. In totality, makes me think yours should be inspected by Canon. Do you have a filter in front of the lens?

December 2nd, 2006, 10:38 AM	#11
Alex Leith Major Player Join Date: Mar 2005 Location: Northampton, England Posts: 500	Thanks Tom, No filter in front of the lens. I was testing in both indoor daylight (well exposed at about F4), and outdoor (again plenty bright enough), so I don't think it's a low light issue. I wouldn't mind hunting occassionally, but every fourth focus this one seems to shunt totally to the wrong end of the focus range and then back again, or it just sits there doing nothing at all. And the pulsing is pretty contstant, especially whilst zooming. __________________ Alex

December 2nd, 2006, 12:31 PM	#12
Oliver Horn Regular Crew Join Date: Oct 2004 Location: Cambridge, UK Posts: 57	Autofocus Behaviour Hi. My A1 seems, er A1! No focus issues. In fact it seems better than my XL2 with stock lens. Trot back to the dealer quick and compare it to another unit. Regards, Oliver Horn.