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Depth of field and Aspect ratio ?


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#1 tony powell

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Posted 30 May 2008 - 11:59 AM

Wondering if anyone can help me with this question ?
I have downloaded some depth of field data for the JVC GY-110 HD camera that has a Fujinon 16x zoom lens. The information specifies that it relates to an aspect ratio of 4:3. My question is, does the depth of field change if you shoot in 16:9, and if so why ?
Thanks in advance to anyone who can help.
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#2 Allen Achterberg

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Posted 30 May 2008 - 02:37 PM

if achieving 4x3 is as simple as merely cropping off the sides of your 16x9 frame then no. it will make no difference . I dont know how that camera is, never used it but if it has a native wide screen image then to achieve 4x3 you'll only need to crop.

if the sensor was a 4x3 sensor and you wanted to crop for 16x9 you'd neet to shoot a bit wider, changing your field of view in order to achieve the same top to bottom framing as in 4x3, and that would change your DOF slightly, you'd have more DOF.

the thing to pay attention to is your chip size, your field of view and your stop. Focal Length is only important in the sense that tighter lenses crush the distance. But matching the same field of view with a 25mm and a 50mm lens for example will have the same DOF, although the 50mm will have a more noticeable effect.
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#3 tony powell

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Posted 30 May 2008 - 06:02 PM

Many thanks for your help Allen, still not sure I understand it though !...
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#4 Allen Achterberg

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Posted 30 May 2008 - 06:51 PM

it's simple, your lens projects an image which covers a certain size. ignore the camera and it's aspect ration and pay attention to the lens, it's circle of confusion, it's stop, and the distance you set the lens for focus. Ignore the camera and the aspect ratio that's happening behind the lens. it's a science of the optics. Just follow your DOF charts, and you will be okay.

DOF can be affected by circumstances that are caused by different aspect ratios. I am only speaking of Spherical lenses here. If you have a 16x9 native camera, and want to mask your project to 2.40 you will need to compensate your framing by resizing your subject to fit in the wider frame. that gives you a new distance which is further away from the plane and you are getting closer to the hyper-focal distance of a lens.

I hope I am not confusing you too much. I may be.
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