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DOF and field of view question


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#1 Adam Paul

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Posted 21 August 2008 - 01:37 PM

Hi there. I have a depth of field and filed of view question regarding 35mm and 1/2" lenses.
In terms of field of view, a 6mm lens in 1/2" is equivalent to which focal length in 35mm?
In terms of depth of field, this same 6mm lens in 1/2" at a F2.8 would be equivalent to the 35mm equivalent at what T-stop? Just trying to figure the DOF differences here. For example, a 18mm or even 22mm 35mm lens is very wide and so the depth of field is quite large. So I'm thinking if there would be much noticeable difference in depth of field when you shoot with a wide 35mm lens as compared to when you shoot with a wide 1/2". It surely doesn't seem to be as noticeable as in a 50mm 35mm lens.
Thanks in advance.

Edited by Adam Paul, 21 August 2008 - 01:39 PM.

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#2 Adam Paul

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Posted 21 August 2008 - 11:59 PM

I guess my main question is, how many stops difference between 35mm and 1/2" to obtain the same depth of field?
Thanks.
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#3 Chris Keth

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Posted 22 August 2008 - 11:09 PM

I forget the formulae so I'm going about this in a series of known rules and estimation.

35mm needs about 3 times the focal length of 1/2" to get the same field of view. That means that at a given stop, 1/2" has between twice and 4x as much depth of field.

Each f/stop change will either multiply or divide DoF by the square root of 2. That works out to 1.4x per stop or 2 per 2 stops.

That sounds like 2-3 stops of DoF difference, so to answer your original question, if the 1/2" video is at an f/2.8 the 35mm should be at a f/5.6 or f/8.

Edited by Chris Keth, 22 August 2008 - 11:10 PM.

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#4 Michael Althaus

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Posted 24 August 2008 - 06:21 AM

With the help of this page ---> http://www.panavision.co.uk/services/ (DOF and FOV calculator) you should be able to figure out the answer to your question (sorry, I was too lazy to go through it).
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