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Calculating DOF for HD


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#1 rsellars

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Posted 26 November 2007 - 02:55 PM

I need to calculate depth of focus (approximately) for an HD shoot. I'm using a Panasonic Varicam (2/3" chips, 720p resolution). I have the film formula for calculating near and far focus at various F-stops. Is there a circle of confusion value that can be used to approximate this camera resolution? I realize that video resolution is measured differently and that circle of confusion may not apply literally. But is there a number that can work to "ballpark" focus prior to shooting? Is 16mm close? Obviously, a large tech monitor would be my final guide.
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#2 John Sprung

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Posted 26 November 2007 - 05:20 PM

16mm isn't exactly close. 2/3" video uses an image area between the size of Super-8 and 16mm, you could split the difference. The closest film format would be 9.5mm.




-- J.S.
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#3 rsellars

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Posted 26 November 2007 - 05:55 PM

[quote name='John Sprung' date='Nov 26 2007, 03:20 PM' post='205342']
16mm isn't exactly close. 2/3" video uses an image area between the size of Super-8 and 16mm, you could split the difference. The closest film format would be 9.5mm.

-- J.S.

John,
Thanks for your reply. I'm wondering if that is the whole story though... When comparing film formats (Super 8, 16mm, 35mm), the size of the negative obviously affects resolution and therefore apparent DOF. The same would be true comparing 1/3" video chips to 2/3" chips. However, when comparing HD video resolution captured on 2/3" chips to SD video resolution also captured on 2/3" chips, the difference in DOF is significant. So there are more factors affecting DOF in video formats than just sensor size. Therefore, can we just compare "image target" size when comparing DOF between film and video formats? Of course viewing format (TV monitor, projection, etc.) is also a factor in determining "apparent DOF."

My project is a commercial (shot on a Varicam) to be broadcast on SD television. But to be safe, I always evaluate my image (focus, etc.) on at least a 720p high def monitor. I've never attempted a side by side comparison, but my experience has been that 720p HD "feels" like it has DOF similar to 16mm. But if anyone has tested this more accurately, I would love to know.
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#4 Michael Nash

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Posted 26 November 2007 - 05:56 PM

You could try this calculator: http://www.panavisio...calcFOVform.asp

It only offers SD 16:9 2/3" video, not HD, but maybe you could double the CoC...
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#5 Daniel Sheehy

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Posted 26 November 2007 - 06:11 PM

This German site seems to give CoC values for DigiBeta, D20 and HDCam as 9.8, 8.25 & 5microns respectively... (Assuming I've figured it correctly, I can't read German <_< )

The Digibeta & HDCam are both 2/3rd inch CCD's.
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#6 rsellars

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Posted 26 November 2007 - 06:55 PM

This German site seems to give CoC values for DigiBeta, D20 and HDCam as 9.8, 8.25 & 5microns respectively... (Assuming I've figured it correctly, I can't read German <_< )

The Digibeta & HDCam are both 2/3rd inch CCD's.


Thanks Daniel & Michael.

Randolph
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Ritter Battery

CineLab

The Slider

Visual Products

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