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Re: [OM] Depth of field preview

Subject: Re: [OM] Depth of field preview
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Thu, 25 Jun 2009 19:51:10 -0400
Thanks for the link.  I might have guessed it was cambridgeincolour. 
There's lots of useful info on that site.  I've read Merklinger's paper 
some time ago but was unaware of the distribution of DOF front to back 
as sensitive to focal length although I certainly knew it varied with 
focus distance.  Now I also know why the focal length is needed by my 
DOF calculator which also tells me the front and rear limits and the 
hyperfocal distance.

Although it won't modify my behavior (because I was already there with 
wide angles at hyperfocal distances) this single sentence made it worth 
the read: "A wide angle lens provides a more gradually fading DoF behind 
the focal plane than in front, which is important for traditional 
landscape photographs."  Now I understand what I'm already doing a bit 
better.

But there was one bit of the cambridgeincolour article that was 
initially a bit confusing.  He says: "The depth of field varies 
depending on camera type, aperture and focusing distance, although print 
size and viewing distance can influence our perception of it."  Although 
he redeems himself later, the implication of the statement is that print 
size and viewing distance are somehow rather secondary to depth of 
field.  In fact, the size of the circle of confusion is the real 
determinant of depth of field... and whether we can see a spot of size 
equal to the circle of confusion is based on print size, viewing 
distance and, of course, our own personal version of human visual 
acuity. (except Moose is a special case and we'll have to leave him out 
or we'll never calculate reasonable values) :-)

Chuck Norcutt

usher99@xxxxxxx wrote:
> Hi Jan,
> 
> Ahh, found it:
> Quick and easy reference:? see first two tables:
> http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
> 
> 
> 
> To derive things from first principles see Merklinger:
> http://www.trenholm.org/hmmerk/TIAOOFe.pdf
> 
> Near and far limits of dof:
> 
> ?
> D1 = (f2D + gfD - gf2)/
> 1 = (f2D + gfD - gf2)/
> ????????? f2 - gf + gD
-- 
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