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Why Do People Say the 5D Has Such a Shallow Depth of Field?


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#1 Peter Ellner

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Posted 21 August 2011 - 01:42 PM

From my understanding, depth of field is not determined by format size, but rather by subject distance, aperture, and focal length. Given this, why do so many people claim that the 5D (VistaVision) has a shallower depth of field than the 7D (Super 35)? And I do have to agree, as it seems like the 5D has a shallower depth of field, even when using the same lens.

Thanks, ignorance is not bliss.
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#2 Peter Ellner

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Posted 21 August 2011 - 01:50 PM

From my understanding, depth of field is not determined by format size, but rather by subject distance, aperture, and focal length. Given this, why do so many people claim that the 5D (VistaVision) has a shallower depth of field than the 7D (Super 35)? And I do have to agree, as it seems like the 5D has a shallower depth of field, even when using the same lens.

Thanks, ignorance is not bliss.


I just realized another reason why this doesn't make sense to me: for larger formats, the size of the acceptable circle of confusion is actually bigger, therefore for any given projected image size, larger formats actually have a greater depth of field, not a shallower one. So the 5D should logically have a deeper depth of field, not a shallower one, but it doesn't...
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#3 Phil Rhodes

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Posted 21 August 2011 - 01:54 PM

Depth of field is a combination of three issues, each of which affects the other.

Your first post is essentially correct; the difference is that to achieve the same framing on a 7D, you'd be using a much wider lens. A 5D has a shallower depth of field given the same field of view, which of course implies a different focal length.

P
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#4 David Mullen ASC

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Posted 21 August 2011 - 06:00 PM

Yes, Phil is correct -- larger sensors use longer focal lengths on average to achieve the same field of view at the same distance as shorter lenses on smaller sensors, and longer focal lengths at the same distance and f-stop as the shorter lens will have less depth of field. Of course, larger formats need a less critical Circle of Confusion figure because the image isn't being as enlarged as much to fill the same sized screen as the smaller sensor camera but the less critical Circle of Confusion figure doesn't compensate enough for the difference in depth of field between the two focal lengths so the net result is still that the larger format has less depth of field on average.

There is a 1.5X conversion factor between Super-35 and FF35, so the depth of field difference works out to be about the same, 1.5-stops. In other words, you'd use a 75mm on a 5D to match the field of view at the same distance as a 50mm on a Super-35 / APS-C camera, and you'd have to stop the 75mm down by 1.5-stops to match the depth of field of the 50mm.
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#5 Martin Hong

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Posted 21 August 2011 - 07:18 PM

If you guys have iPhone or Android phones, you can download DOF calculators applications. They also come with frame size option.. I think that's the fastest way to calculate the DOF.. I wouldn't know if they are accurate though.. :/

Edited by Martin Hong, 21 August 2011 - 07:19 PM.

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#6 Peter Ellner

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Posted 21 August 2011 - 07:32 PM

Thank you, I had suspicions about this, but it makes total sense. Thanks.
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