New article by Jeff Conrad: Introduction to DOF

[QT Luong]

A new article by Jeff Conrad has been posted
Intoduction to DOF (http://www.largeformatphotography.info/articles/IntroToDoF.pdf).
Please feel free to leave any contructive comments in this thread.

[Emmanuel BIGLER]

This is an excellent paper for those who enjoy to understand where DOF theory exactly comes from, and who are not satisfied with copies of copies of old things carried from one old book to another old out-of-print book and eventually from one un-verified website to another ;-).

DOF being probably THE FAQ#1 in MF/LF photography, Tuan's LF web site does provide a Public Service by publishing this ;-)

[Tadge Dryja]

This is a great paper. Though most of it I was already familiar with, it's nice to se it all presented well, and it's something I can send a link to for people struggling with it.

I still stick to telling people the same two basic ideas: All else being equal, bigger lenses will let you have less depth of field. And all else being equal, the more light your photo is made out of, the nicer it will tend to look.

[Arne Croell]

Jeff, this is a really well written article with everything that is needed. Thanks a lot.

[Leonard Evens]

This is an excellent introduction to the basic principles of DOF. It handles several important points that are often glossed over.

Of course one could always ask for more, but that would lead to a book length treatise. This essay provides virtually everything that even the most technically minded large format photographer needs to know about basic DOF.

Now Jeff should address his considerable talents to describing DOF when the film plane and lens plane are not parallel. The basic ideas are quite simple, and several attempts have been made to explain them, including mine, but I don't know if anyone has succeeded at the level of clarity in Jeff's essay.

[Jeff Conrad]

Thanks to Emmanuel and Struan Gray for reviewing the section on an
asymmetrical lens.

I would urge anyone interested in DoF to look at Paul van Walree's
excellent treatment of the subject at http://www.vanwalree.com/optics/dof.html. We reach much the same
conclusions, but Paul includes several excellent images illustrating what I
cover only mathematically.

[Graham Patterson]

I hadn't looked at the cross-format relationships before - just relied on my empirically determined instinct. Clear, concise, and readable. All the makings of a classic!

[tom barbara]

Very similar to treatments I have read in older out of print books eg. "Photographic Priciples" (DOVER). A more complete treatment of choices for the circle of confusion diameter than most.
I prefer to express everything in terms of the magnification from the out set, even Eqs 4 and 5, which then read

Un = U/(1 + ( c/d*M) ) and Uf = U/( 1 - (c/d*M) )

where d is the aperture diameter and M the magnification. From these one can see more clearly the independent contributions. Plus these are so easy to remember!

The formula for M = (f/u)/ ( 1 - f/u ) completes the picture.

[Don Wallace]

I will defer to others on the accuracy of the information but I don't see this as an introduction to the subject. I want to know how to use depth of field in the field, not on paper. I want to know how to use dof in typical situations. I don't find articles like this helpful at all.

[Dan Fromm]

Don, buy a copy of Al Blaker's little book Applied Depth of Field. Long out of print, try Amazon.com or abebooks.com or addall.com

[Jeff Conrad]

One man's introduction is another's dissertation on irrelevant esoterica ...

Most of the material was included for those who might wonder where some

oft-quoted formulae (as well as a few myths) come from.

In a practical sense, I tend to agree with Don. At least in my experience,

90% of what's needed in the field is covered by Eqs. 20 and 22, whether

you're using LF or a hand camera (one that has DoF scales, anyway ...), and

whether or not the lens is tilted.

As several other threads here have indicated, it's also important to choose

a CoC suitable for your own viewing conditions. In particular, if you will

be viewing large prints at 10", or even worse, using a loupe, the standard

values simply won't suffice.