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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 22 Jan 2009 (Thursday) 19:43
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DOF and proportional subject distance

 
anothernewb
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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?


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DreDaze
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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 (external link)


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Jim ­ G
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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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xarqi
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Jan 22, 2009 19:53 |  #4

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




  
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gator1970
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Jan 22, 2009 20:09 |  #5

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

Thanks dredaze, that's a really interesting link.




  
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gasrocks
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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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anothernewb
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Jan 23, 2009 13:18 |  #7

awesome site. thanks for the help


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lewdog
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Jan 24, 2009 16:27 |  #8

gasrocks wrote in post #7166548 (external link)
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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gasrocks
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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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lewdog
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Jan 24, 2009 16:36 |  #10

gasrocks wrote in post #7178846 (external link)
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.


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Stocky
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Jan 24, 2009 16:53 |  #11

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


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DreDaze
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Jan 24, 2009 16:55 |  #12

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


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lewdog
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Jan 24, 2009 16:56 |  #13

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

I don't think it does.


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Lowner
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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.


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lewdog
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Jan 24, 2009 17:00 |  #15

Lowner wrote in post #7179028 (external link)
lewdog,

Oh yes it does.

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


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DOF and proportional subject distance
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