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Canon GL Series DV Camcorders
Canon GL2, GL1 and PAL versions XM2, XM1.


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Old February 14th, 2006, 03:04 AM   #1
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Ever notice this focus issue?

Have you ever noticed that sometimes if you zoom all the way in (optical zoom, no digital zoom) on something you can't get it to come into focus, even using the manual focus?

Also, I had a shot at the wedding I'm working on where I zoomed in on the bride's ring, got it focused, and then did a zoom out to reveal her getting her hair done. The problem is that a second or two after I start the zoom the image goes out of focus for a second or so and then comes back into focus as I keep zooming out. I've noticed this happen before on similar shots. Ever had that happen?

Of course, I would also love to hear explanations for why this is happening if anyone can tell me. d:-)
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Old February 14th, 2006, 03:45 AM   #2
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Quote:
Originally Posted by Travis Cossel
Have you ever noticed that sometimes if you zoom all the way in (optical zoom, no digital zoom) on something you can't get it to come into focus, even using the manual focus?
Yes.

Quote:
Originally Posted by Travis Cossel
Also, I had a shot at the wedding I'm working on where I zoomed in on the bride's ring, got it focused, and then did a zoom out to reveal her getting her hair done. The problem is that a second or two after I start the zoom the image goes out of focus for a second or so and then comes back into focus as I keep zooming out. I've noticed this happen before on similar shots. Ever had that happen?
Yes.

Quote:
Originally Posted by Travis Cossel
Of course, I would also love to hear explanations for why this is happening if anyone can tell me. d:-)
Well, it would appear you are doing the correct thing. But, just so we are on the "same page" I want you to do something for me.

Repeat the same scenario, at home now, at similar distances. This is what I do. I "set-up" the shot by zooming on the FURTHEST point I wish to be IN-FOCUS - are you saying it is the ring on the finger? Ok, zoom in on something, anything with detail, newsprint is good, and we'll call that the RING shot. Ok, remove MF and then reapply it. Now, everything from the RING to your camera should be in focus, and certainly when you slowly zoom out the RING distance picture should be in focus. However, if you have anything "BEHIND" or further than the RING distance, that would be soft. Was the Bride's head BEHIND this ring distance? See where I'm going with this? I'd bet that the "time" delay in getting back in focus is not even that. I bet that at a certain point the ring AND the Bride's head "appears" to be in focus.

So, and on close-up work - this sounds like it was - I'd MF on the furthest point - was it the Bride's head? - reposition for the RING shot and then zoom out from there.

If that doesn't work, I give up! Well not quite . . get back at us!

Grazie
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Old February 14th, 2006, 04:43 AM   #3
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Gotta love this forum. It's 3:30am and I'm working on a wedding video and you ask me to pull out my camera and try some stuff and what do I do? I pull out my camera, of course!


Here's a better description of the original shot in question:

I was standing about 3 or 4 feet away from the bride. She was sitting in a chair getting her hair done. I wanted to go from a close-up of the ring on her finger (her hand was in her lap) to a wide shot of her in the chair getting ready.

So, I zoom in on the ring and get it in focus using manual focus. I hold the shot for a few seconds and then start zooming out slowly. Almost immediately the image goes out of focus and then somewhat back into focus. I tried this shot several times, and had the same thing happen every time. It went out of focus as I started zooming out.


So, I tried the same thing again. I took the TV remote control and laid it on a pillow with plenty of lighting in the room. I was about 3 or 4 feet away, and I zoomed in in auto-focus. I can't get all the way zoomed in and hold focus with the auto-focus. So, I get it zoomed in as far as possible with auto-focus doing it's thing. Then I turn off auto-focus and try to zoom in a little more while adjusting the focus manually. No go. If I zoom in even just a little more and try to improve the focus nothing happens. It's like I'm not even turning the ring. I tried this several times and the same thing happened every time.


So, if I zoom in on something far away, like a tree (say 50 yards away) I can get good focus with either auto-focus OR manual focus. BUT, if I try to zoom in on something close, the focus becomes UNADJUSTABLE at a certain point in the focus.

Any ideas?
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Old February 14th, 2006, 06:03 AM   #4
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At full zoom the minimum focus distance is a bit over 3 feet. If closer than 3 feet, you will not get good focus when zoomed in. Is this part of the issue?
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Old February 14th, 2006, 10:16 AM   #5
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The GL2 lens's focus adjustment is inconsistent at full zoom: if you zoom fully and adjust focus on a somewhat close object (5 to 10 feet), then zoom out, you're going to lose your focus, then get it back (you get it back because the DOF is larger with a shorter focal length). Of course this effect is more noticeable with wider apertures.

With a more consistent lens, focus would be retained for the full zoom range of the lens; for instance, I don't have this problem with my SLR still camera zoom lens.
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Old February 14th, 2006, 10:22 AM   #6
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J-F ! Very well put! -g
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Old February 14th, 2006, 10:24 AM   #7
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Same motor used for both

Somewhere else on this forum was mentioned the fact that there is one motor that handles both zoom and focus. It cannot do both at the same time. While using autofocus, the image can go out of focus during zoom in/out because the motor is too busy to fix the focus. Once you stop the zoom in/out the motor is then available for autofocus functions.

That is my laymans understanding of autofocus problems with a GL-1 and GL-2 (XM-1 and 2 for PAL). Apparently this is not a design flaw since most (all?) cameras in the same price range use one motor for both functions. Having two motors would put the camera in a different price range??????

For weddings, I always instruct my other camera operators to set up the vows and ring exchange by zooming in on the bride/groom's face, let autofocus set the focus (lcd is too small to set it manually with any confidence) then select manual focus and zoom out to frame the vows/ring exchange shots. That way nothing in the background between the bride and groom's faces will cause the camera to go out of focus during those critical shots.
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Old February 14th, 2006, 02:15 PM   #8
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Great replies everyone!

Don, I think you hit it right on the head. I was pretty close to the subject while zoomed in quite a bit. I guess my creative idea needs a better lens to work with.

Also, that's interesting about the single motor. I didn't realize that. That explains a lot about how even during a slow zoom with auto-focus on the focus can get soft but corrects when the zoom stops.

And yeah, I set up focus right away during the ceremony with manual focus to avoid any issues of refocus with background. The shot in question originally was durng pre-ceremony.

Thanks again guys!
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Old February 14th, 2006, 09:06 PM   #9
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The GL1 lens has separate motors for focus and for zoom (i.e., 2 motors) - I doubt if the the GL2 lens is significantly different.

However, zooming might create a challenge for auto focus because the content of the focus sensing zone may change significantly during the zoom process and induce hunting as the camera seeks focus confirmation.
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Old February 15th, 2006, 02:57 PM   #10
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it sounds like to me that the items are two close. if is about 3 feet that might be the problem
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Old February 15th, 2006, 04:57 PM   #11
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I guess I'm still a little confused about my original problem, though. I had the object IN FOCUS with the manual focus ON. This would suggest to me that I could zoom out as quick or as much as I wanted without losing focus. Zooming in, yes, I could see that causing problems.

The problem, however, was that the frame was in focus and as I started to zoom out it went out of focus and then came somewhat back into focus. How is this possible if the manual focus is engaged?
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Old February 15th, 2006, 05:27 PM   #12
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Travis, I think it comes down to what I said: focus for the Gl2 lens isn't consistent over the whole focal length range.
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Old February 15th, 2006, 05:39 PM   #13
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I see. Okay then, thanks!
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