DoF Charts and f/stops

[Mark Sawyer]

I never use Depth of Field charts, tables, calculators, etc., but a question had me lying in bed awake and wondering last night...

Say you're doing close up work at 1:1, and you set your f/stop to f/16. With the bellows/focal length at twice the normal extension, your effective f/stop is f/32. Which do you use for the chart/table/calculator, f/16 or f/32?

[cowanw]

DOF is determined by subject magnification at the film / sensor plane, at any given f stop.
The f-number of an optical system (such as a camera lens) is the ratio of the system's focal length to the diameter of the entrance pupil. For exposure purposes we call the adjusted f stop at close distances an effective f stop, but for optical purposes it is still bound by the original definition. Take a look at the barrel of an older 35mm lens and see how the focus numbers relate to the DOF scale that used to be engraved on each lens.
So in your case use f 16.

[Pere Casals]

but for optical purposes it is still bound by the original definition. Take a look at the barrel of an older 35mm lens and see how the focus numbers relate to the DOF scale that used to be engraved on each lens.

So is the rule using engraved f/ and magnification...

[Bob Salomon]

The Rodenstock DOF/Scheimpflug pocket calculator tells you f stop, focus point, tilt amount, etc for every format from 35mm to 810 and fits flatly in your shirt pocket assuring you of a good night’s sleep!

[Pere Casals]

Being DOF scales of great help, IMHO it should be noted that all DOF scales are approximate, because formulas have simplifications and limitations.

Proficient cinematographers use Through Focus MTF charts for the specific lenses.

[Bob Salomon]

Being DOF scales of great help, IMHO it should be noted that all DOF scales are approximate, because formulas have simplifications and limitations.

Proficient cinematographers use Through Focus MTF charts for the specific lenses.

Attachment 184770

The Rodenstock one lets you set for different CoC sizes so that is no problem.

[cowanw]

Are you two channeling Abbot and Costello or Laurel and Hardy?

[John Layton]

...or Penn and Teller?

[Pere Casals]

Bob, I'm not talking about the CoC one may require, but about how CoC actually behaves for each particular lens compared with theoric/generic calculations. Still the pocket guide is of great help, no doubt.

Are you two channeling Abbot and Costello or Laurel and Hardy?

...or Penn and Teller?

Hey guys, TF MTF charts are serious stuff, explaining why one has to learn how his lens behaves beyond what stated in generic DOF calculators.

You may find several proficient members here explaining why DOF calculations have remarkable flaws in the theoric CoC/DOF calculations for particular glasses... I you need the links just tell it.

Or just understand what this curve plots:



This is specially critical for macro, a particular lens may behave better or worse in the front or in the rear of the focus plane. I was thinking that this was well known.

... and let me add that bokeh's nature also may vary front vs rear.

[Dan Fromm]

Papi, I think you're confusing CoC, an arbitrary number chosen by the photographer based on how much the negative is to be enlarged, and the blur circle, which is given by the lens.