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Thread started 22 Jan 2009 (Thursday) 19:43
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# DOF and proportional subject distance

Jan 22, 2009 19:43 |  #1

OK - newbie Q #1 here - and forgive me if this is explained in one of the many newbie guides out there - I simply haven't looked at all of them yet.

Is the relationship between aperture and DOF on a lens proportional to the focusing distance of the subject - or is it fixed?

Ie - if the DOF of my lens is say 1cm wide open if my subject is 1 foot away, is the DOF larger (20cm) if my subject is say 20 feet away, or is it still 1cm at any distance?

Gripped 80D,10-18 STM, 55-250 IS STM, 15-85 IS USM, 85 1.8, 10-400 II, 430 EX II

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Jan 22, 2009 19:47 |  #2

it is larger...here's a link that's kind of good to mess around with
http://www.dofmaster.c​om/dofjs.html

Andre or Dre
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Jan 22, 2009 19:48 |  #3

DOF gets narrower the closer you get to the lens (macro involves tiny DOF) and the wider the aperture gets.

So if you're focusing 10m away at f/2 you will have wider DOF than you will focusing at 1m f/2.

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Jan 22, 2009 19:53 |  #4

Neither proportional nor constant.
http://en.wikipedia.or​g/wiki/Depth_of_field
http://www.dofmaster.c​om/dofjs.html

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Jan 22, 2009 20:09 |  #5

DreDaze wrote in post #7166349
it is larger...here's a link that's kind of good to mess around with
http://www.dofmaster.c​om/dofjs.html

Thanks dredaze, that's a really interesting link.

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Jan 22, 2009 20:21 |  #6

DOF depends on three things: Aperture, focal length of lens (telephotos have less DOF, wides have more) and working distance. Closer = less DOF. One reason why macro is a challenge.

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Jan 23, 2009 13:18 |  #7

awesome site. thanks for the help

Gripped 80D,10-18 STM, 55-250 IS STM, 15-85 IS USM, 85 1.8, 10-400 II, 430 EX II

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Jan 24, 2009 16:27 |  #8

gasrocks wrote in post #7166548
DOF depends on three things: Aperture, focal length of lens (telephotos have less DOF, wides have more) and working distance. Closer = less DOF. One reason why macro is a challenge.

And sensor size, I believe.

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Canon L: 35/1.4 85/1.2 135/2 70-200/4IS
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Jan 24, 2009 16:33 |  #9

lewdog - you caught me, thanks. Yes, those little P&S cameras with 1/4 the size sensor can have 4 stops more DOF at the same aperture.

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Jan 24, 2009 16:36 |  #10

gasrocks wrote in post #7178846
lewdog - you caught me, thanks. Yes, those little P&S cameras with 1/4 the size sensor can have 4 stops more DOF at the same aperture.

I wonder-if we're talking 35mm equivalent focal length, does that take sensor size out of the calculation? I'm not sure exactly how the formula works.

5DII
Zeiss ZE: 21/2.8 50/2 100/2
Canon L: 35/1.4 85/1.2 135/2 70-200/4IS
3x430 EXII and various small studio equipment
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Jan 24, 2009 16:53 |  #11

Someone should also mention print size if we are trying to be all inclusive.

Always happy to hear some critique
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Jan 24, 2009 16:55 |  #12

how does print size relate to d.o.f.?

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Jan 24, 2009 16:56 |  #13

DreDaze wrote in post #7178996
how does print size relate to d.o.f.?

I don't think it does.

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Zeiss ZE: 21/2.8 50/2 100/2
Canon L: 35/1.4 85/1.2 135/2 70-200/4IS
3x430 EXII and various small studio equipment
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Jan 24, 2009 16:58 |  #14

lewdog,

Oh yes it does.

Edited to add: OK, thats a little too brief, so a little more information.

Depth of field scales were originally worked out using film (obviously) and assumed a circle of confusion based on a standard 10" x 8" enlargement. Because the appearance of sharpness is only an appearance, the size of the print is crucial.

These days I'm printing at A3+ so the Depth of Field is effectively less than the original calculations suggest.

Richard

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Jan 24, 2009 17:00 |  #15

Lowner wrote in post #7179028
lewdog,

Oh yes it does.

Can you explain? Not trying to argue, this just surprises me.

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Zeiss ZE: 21/2.8 50/2 100/2
Canon L: 35/1.4 85/1.2 135/2 70-200/4IS
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DOF and proportional subject distance
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