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strange sort of out of focus


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#1 shootist

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Posted 05 May 2006 - 08:18 AM

Did a job recently and later saw it on TV. There was a shot that was out of focus, the BG was sharper than the subject in the forground. Figured I screwed up. But I was watching another episode and saw it again and then saw it a 3rd time in a shot done by another cameraman. There is a common thread in what I saw (besides being shot with a DVX). Every problem scene had bright or shiny backgrounds. My first shot was at an ice rink with the bright white ice in BG. I had lighting on the subject in foreground to balance but obviously the ice was hot, around 100 IRE. The other time, I am sure I was focused, as I remember checking it. The 3rd shot I noticed was a sitdown interview with a trophy case behind. Many of the trophies had specular highlights and they were sharper than the subject. This was a good shooter and I doubt he focused on the trophies. Many other interviews, with darker BG were perfectly fine, which tells me it isn't the lens. And no, it wasn't auto focus. Subject was filling the frame so the auto focus, if accidently on, would have focused on the forground subject.
Since noticing this, I've been watching for it on reality, documentary shows on cable and I've seen it several other times. Always with a bright background.

Anybody else seeing this anomaly?
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#2 Mike Kaminski

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Posted 09 May 2006 - 07:01 PM

Did a job recently and later saw it on TV. There was a shot that was out of focus, the BG was sharper than the subject in the forground. Figured I screwed up. But I was watching another episode and saw it again and then saw it a 3rd time in a shot done by another cameraman. There is a common thread in what I saw (besides being shot with a DVX). Every problem scene had bright or shiny backgrounds. My first shot was at an ice rink with the bright white ice in BG. I had lighting on the subject in foreground to balance but obviously the ice was hot, around 100 IRE. The other time, I am sure I was focused, as I remember checking it. The 3rd shot I noticed was a sitdown interview with a trophy case behind. Many of the trophies had specular highlights and they were sharper than the subject. This was a good shooter and I doubt he focused on the trophies. Many other interviews, with darker BG were perfectly fine, which tells me it isn't the lens. And no, it wasn't auto focus. Subject was filling the frame so the auto focus, if accidently on, would have focused on the forground subject.
Since noticing this, I've been watching for it on reality, documentary shows on cable and I've seen it several other times. Always with a bright background.

Anybody else seeing this anomaly?


Sounds like it might be a back focus issue, but i dont think the dvx even has this option. It could simply be that the huge depth of field of the CCD keeps the BG and subject in the same amount of focus and the background appears sharper and more contrasty simply because it is hot, hence giving the illusion that the BG is sharper. Otherwise, I dont know.
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#3 Tim Tyler

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Posted 09 May 2006 - 10:44 PM

With the DVX, when you zoom in and focus, the focus does not always hold when you zoom back to mid or wide. I and others I know have been bitten by that a few times.

Back focus on the DVX can be adjusted by a service tech using software.

I think there are some threads about all this from a year or two ago on this forum.
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#4 David Mullen ASC

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Posted 09 May 2006 - 11:15 PM

Sounds like a back-focus problem -- but I've also had a problem when the shot has a lot of depth of field because a face can look less sharp (due to a lack of hard lines) than the background, so the face looks out-of-focus, or less in-focus, when it isn't.
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#5 shootist

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Posted 17 May 2006 - 01:44 PM

Sounds like a back-focus problem -- but I've also had a problem when the shot has a lot of depth of field because a face can look less sharp (due to a lack of hard lines) than the background, so the face looks out-of-focus, or less in-focus, when it isn't.



As I mentioned in my original post, similar interviews shot with dark BG were perfectly fine. Plus I saw other cameras do the same thing. The common thread was the bright BG.
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#6 Stephen Williams

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Posted 18 May 2006 - 02:36 AM

Sounds like a back-focus problem -- but I've also had a problem when the shot has a lot of depth of field because a face can look less sharp (due to a lack of hard lines) than the background, so the face looks out-of-focus, or less in-focus, when it isn't.


Hi,

These cameras don't have a real zoom lens. They have what is called a vario-focual lens. Its cheaper to make with less elements. Optically better than low cost zooms. There is an engineering set up to set the focus for each focal length during a 'zoom'.

Stephen
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