Myth of depth of field with tele lenses

[joseph_smith3]

In the April 2008 issue of Naturescapes.net, Paul Skoczylas has written an

excellent technical article "The Mathematics of Depth of Field

Part Two: Crop Factor, Magnification and the 1/3 Myth." As a long lens shooter,

I have always wondered why my depth of field was not working out as I had

expected--one third in front and two thirds behind the point of focus. Now you

can find out why, and learn a lot of other things too. Go here for the article:

http://naturescapes.net/042008/jm0408.htm

 

The April cover shot is pretty good too!

 

Joe Smith

[david_dorcich1]

That's an article about the ethics of digital manipulation.

[david_dorcich1]

http://naturescapes.net/042008/ps0408.htm

 

part 1: http://www.naturescapes.net/102004/ps1004.htm

[bobatkins]

It's myth in the sense that its never been true and the fact that it's never been true has never been a secret!

 

DOF varies from 1:1 in the macro range to 1:Infinity when you're focused past the hyperfocal distance. It's 1/3:2/3 only at one specific focus distance (which depends on the focal length of the lens).

[jeff_conrad]

In general, you want to focus on the harmonic mean of the desired near and

far limits of DoF. Sound intimidating? Not to worry; with Canon's DEP

mode, you simply focus on the near limit, focus on the far limit, and

depress the focus button (the shutter release or wherever you've moved this

function) once again to set this distance as well as the proper

<var>f</var>-number! Oh wait ... this is the feature that was eliminated

with the introduction of the EOS-1D Mk II ...

[Mary Doo]

<b><i>"As distance to the subject increases, DOF increases. <br>As f-stop increases, DOF increases. <br>As focal length increases, DOF decreases. <br>As sensor/film size increases, DOF decreases." </i></b>

 

<p>Very Nice! It seems the fancy graphics and equations basically confirm what most of us already know in layman's photographic knowledge.

 

<p>For general landscape photography (not using an extra long focal length), the 1/3 : 2/3 ratio, coupled with a high F-stop, works for me. For macro photography of 1:1 or more, Lester Lefkowitz has documented that the ratio changes to the subject's half-point (1/2 : 1/2) for maximum sharpness.

 

<p>Mary

[profhlynnjones]

DOF is based on the research of Dawes relating to diffraction and nothing else.

 

It relates to diameter of aperture and distance to subject, not related to focal length. As an example, if there is 1 inch of aperture and 10 feet of distance, ideally, the DOF will be identical whether a 50mm at f 2.0 or f 8.0 at 200mm assuming 10 feet.

 

These are theoretical maximums. The higher the resolution/contrast the closer to the theoretical mamimum. If there are poor quality optics, not sharp, the greater the visual DOF.

 

The reason for apparent greater DOF with WA lenses is because the "f stop" with a shorter focal length has an aperture significantly narrower with a similar f stop and a longer focal length.

 

Lynn