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Canon XL1S / XL1 Watchdog
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Old January 4th, 2005, 03:45 AM   #1
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Maintain focus all time.

Sorry but my written english is very very bad.

I would like to do a question about how you get maintain focus when you record for example a theater play continuously (1 hour). My filming position is to the left of stage, an actor may be at 4 meters and other to 12 meters, if I want to do a panoramic I must to adjust the focus but the XL1s focus is very bad (or I am very bad).

How I solve this problem?

I have a Canon XL1S. Also I thing that the factory visor is very ver bad ... I never know if I'm in focus.
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Old January 4th, 2005, 05:46 AM   #2
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On a DV camera you have a large depth-of-field (the range in
which your scene is in focus), so if you zoomed in, set focus and
then zoomed out you should be able to get the full stage in
focus all of the time.

If that is not possible for some reason (which sounds strange)
then either select auto focus on the camera or do some tests
runs to manually change focus on the fly.

The full manual lens will be much better to do this manually then
the default "white" auto lens.

Although I could focus okay with the stock viewfinder (that's
what it is called, not visor) you can buy the black & white CRT
viewfinder which will give you perfect focus ability!
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Old January 4th, 2005, 09:53 AM   #3
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>>>If that is not possible for some reason (which sounds strange)
then either select auto focus on the camera or do...<<<

This sounds like the back-focus problem I was having to where when setting focus zoomed in and it being out when pulling back. Do you think he needs to send it in to Canon Rob?
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Old January 4th, 2005, 02:15 PM   #4
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I'm really not qualified to talk about that Randy. Never had back
focus problems myself and other lens wizards here are far better
in discussing that than me <g> Hopefully they'll join soon!
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Old January 8th, 2005, 02:00 PM   #5
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Isn't that that problem that the lens changes the iris opening if you zoom in, and if you then zoom out it changes automatically and the focus also changes, with your iris?

Correct me if I'm wrong, I'm just guessing.
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Old January 8th, 2005, 02:40 PM   #6
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Pepe, your English is much better than my Spanish.

It is almost impossible to record a play with more than one character with only one camera.

"an actor may be at 4 meters and other to 12 meters"
If you mean you want to have both actors in focus, you should focus somewhere between 4 and 12 meters and hope that "depth of field" will keep both of them in focus. It depends on your focal length and iris setting. Otherwise, focus on the actor at 12 meters, and widen to include the actor at 4 meters.

If you focus at either 4 or 12 meters, then pull wide, your camera should be in focus. You should not have to adjust focus for the wide shot. If the camera is out of focus when you go wide, you have a problem with "backfocus." With the Canon cameras, the lens needs to be adjusted by a technician.

We shot a one-woman play with two PD150's and one Canon XLs. When I saw the director months later, he said all the footage from the Canon camera was out of focus, and the two PD150's were great. The Canon was shooting the wide shot, so he must have had a problem with "backfocus." This is a problem you can get with interchangeable lenses.

Mathieu, the focus does (should) not change with the iris.

Wayne Orr, SOC
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Old January 8th, 2005, 05:00 PM   #7
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Oops, mistake :-).
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Old January 21st, 2005, 04:25 AM   #8
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Not so Fast Wayne....

In reality if you change apeture (iris) settings you affect depth of field, and accordingly, you can change the apparent focus of the shot. For instance if your subject was within the deeper depth of field of a small apeture but at one extreme of it, and then you went to a wider apeture and subsequent shorter depth of field, your subject could concevibly end up soft.

Never say never, Never say die, infact ....never.....





lol
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Old January 21st, 2005, 09:58 PM   #9
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Well, yes and no, Matthew. The effect Mathieu was refering to occurs on fixed lens cameras, such as the DVX, Sony, and others. With these cameras, you can "manually" set the lens wide open, but when you zoom in full tite, they will stop down to avoid an effect called "portholing." Then, when you zoom back, they will begin to return to the wide open iris which you originally set. This only occurs at the last part of the zoom range. But even though the iris setting has changed those last couple of mm of the zoom range, when you focus carefully, then pull back, the subject you focused on should remain sharp. Otherwise, you have a tracking problem.

With the Canon XL cameras with real manual iris settings, the lens will remain wide open when you zoom in full tite, and I would imagine you will see the effects of portholing. (It looks like you are getting a vignette effect)

OTOH, Matthew, I believe this is what you are correctly refering to:
Let's say on Mathieu's stage there are three actors, at ten feet, fifteen feet, and thirty-five feet from his camera position. He has his iris set at f/5.6, and zooms in tight on the actor at fifteen feet, and pulls back wide enough to include the other two actors. His lens focal length is approximately 20mm, and all three actors appear to be in focus.

But, if we change the iris to f/1.4, and zoom into the actor at fifteen feet and set the focus, when we pull back, only that actor at fifteen feet will be in focus, as the depth of field at this iris setting is too shallow to hold the other two actors in focus.

OK, Matthew? You can check my figures by going to http://www.panavision.co.nz/main/kbase/reference/calcFOVresult.asp
where you will find a very handy "depth of field guide."

Wayne Orr, SOC
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Old January 22nd, 2005, 12:10 AM   #10
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Wow. Great explanation, Wayne. Much appreciated,
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