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Old January 23rd, 2004, 12:18 PM   #1
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focusing while zooming

How do you go about keeping focus on a subject while zooming in/out?

Do you have to use auto focus for this? How do you know auto focus won't be focusing on something else?

Are there accessories that allows you to do this easily?

Thanks,
Vincent
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Old January 23rd, 2004, 12:26 PM   #2
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Vincent,

Zoom in your subject at the maximum value, set up your focus (turn auto focus off), and if the distance between the subject and the camcorder remain the same, you won't loose your focus while zooming in and out.
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Old January 23rd, 2004, 12:54 PM   #3
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Hmm... this may be related to the same topic, but I also have another question. Some cameras present both a zoom and a manual focus ring, like the VX2100. Now, on the GL2, it only has a focus ring, and I've read some reviews that both of these cameras you cannot override the focus ring. What does this mean? Does this mean you can't keep focus while zooming or you cannot position where you want your focus to be?
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Old January 23rd, 2004, 02:08 PM   #4
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You first zoom in all the way to your subject, get critical focus (manually of course), then zoom back to your wide angle and do your zoom shot. If it's a decent lens, it will stay in focus. Some of the early "prosumer" cameras had a problem with critical focus while zooming, but I think all the newer ones work they way they're supposed to. I had trouble maintaining focus with an early XL1 and VX1000 a few years ago, but all other 1/3" chip cameras I've used work fine.
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Old January 25th, 2004, 09:03 AM   #5
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A great help to answer your question might be to let us know
which camera and lens you are using...
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Old January 26th, 2004, 09:38 AM   #6
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I'm not certain if Vincent is experiencing what I've noticed
with my GL2.

I can only speak about the Canon GL2 and the Sony PD150. I
have tried to use the zoom rocker and the manual focus ring
simultaneously and these cameras won't let you adjust focus
manually while zooming. Once the zoom is engaged, twisting
the manual focus ring has no affect. I've experimented with
using a LANC controller. Yes, I have the focus set to manual.
As soon as I release the zoom rocker, the manual focus ring
will reactivate. I suspect some conflict between the zoom and
focus motors. If others have made a simultaneous zoom/focus
with these cameras, then I would certainly like to know the
technique.

Thanks

Joseph
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Old January 26th, 2004, 09:59 AM   #7
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Howdy from Texas,

Due to the way these lenses work, it is *not possible* to pull focus and zoom at the same time on any prosumer camcorder using an auto-servo lens. This holds true for 3CCD camcorders such as the Canon GL1, GL2, Sony PD170, VX2000, etc. on down to the consumer 1CCD camcorders. Also true for the Canon 16x automatic (white) lens. It does not matter if there are separate manual focus and/or zoom rings nor does it matter if you're using a remote LANC lens controller; it simply isn't possible.

On the Canon 16x manual (black) lens and standard Fujinon or Canon 1/2" and 2/3" broadcast video lenses, it is possible and of course very common to pull focus and zoom at the same time. Hope this helps,
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Old January 26th, 2004, 10:16 AM   #8
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That's why electronic lenses are so annoying. However, with some practice you can make them work in most cases. But these are two issues--one, maintaining critical focus and the other doing a focus shift. The lens either maintains critical focus or it doesn't because there's no back focus adjustment. I do have personal knowledge of one early XL1 that would't work right and the owner sent it in, and they adjusted back focus or replaced the lens or something, and it worked better, although you still could'nt zoom in, focus, and zoom out all the way and keep it totally sharp. I assume the newer models are better at that; I know the PD150s I've seen all seem to work fine.

As far as shifting focus, what I do with a DSR250 is zoom in, pan, and hit the auto focus button and let the lens shift itself electronically. This works in most situations, but obviously not in all. For example, if you zoom and pan and end up with a composition in which you want the subject way over to the side, then the auto focus will screw you up.

I rarely use the 250 for a dolly or jib shot, but there have been a few situations in which I did because with the wide angle adapter I could get right up a few inches from a person's nose and keep focus, wheras my camera with the real lens won't do that. I did a jib shot in which I boomed from a really extreme shot right in the person's face to a really high, wide angle with the camera moving up to the ceiling. There was no way to follow focus on the move, so I thought, what the heck, I'll try it on auto. Because of the particular situation, the auto focus kept it right on. So if you're careful and work on it, you can learn to use the electronic lenses for most things. I wouldn't trade one for a real lens, but you can live with their limitations in most cases, if you have to.
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Old January 30th, 2004, 03:32 AM   #9
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Quote:
Due to the way these lenses work, it is *not possible* to pull focus and zoom at the same time on any prosumer camcorder using an auto-servo lens
I read this and then tried it with my camera and I can do both at the same time. Zooming and manually focusing.

Am I missing something here?
Thanks,
Rob
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Old January 30th, 2004, 07:44 AM   #10
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*shrug* I don't know, Rob, there are always exceptions I guess. That camcorder does not have LANC, which might be part of the explanation. Plus one of it's features is a "real-touch manual focus ring" which might have something else to do with it -- I'm unfamiliar with that camcorder; it's a single-chip 1.3mp consumer piece.
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Old January 30th, 2004, 10:11 AM   #11
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Sometimes you can hit it, but I should have elaborated. I was thinking about traditional focus pulling, where you zoom in to the second focus point, note the distance on your lens, and then when you shift focus the assistant or you if you're good can hit the mark easily. On most electronic lenses the focus ring is electronic and in most cases doesn't go to the same point twice in a row, and there are no marks. If you mark the lens, it usually doesn't work, and if you turn the ring back to your beginning focus point and then go back to your end focus, it's normally not the same.
I've been able to use the auto focus button carefully with a DSR250 for focus shift, and in most cases it works better than doing it manually. As I move off the foreground subject, I press the button and let the camera shift in as I move to the background subject. It won't work if the shot it too loose, but in many cases it works very well.
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