[Leica] About depth of field scales and Merklinger

[Jim Brick <jimbrick@photoaccess.com>]

Just a few comments.

It is true that the DOF scales on camera lenses were computed from DOF
formulas derived when lenses and films were a whole lot less sharp than our
modern lenses and films. They are off by at least two stops for anything
resembling critical work.

A few years ago I read Merklinger's books and as I said earlier, I was
unimpressed. The problem is that to be a good photograph, what is sharp and
what is not sharp are subject related. A portrait can have (probably should
have) the foreground and background very out of focus. But a sweeping
landscape should be sharp everywhere. If you follow Merklinger's direction,
[focus at infinity] you will have blurry foregrounds in landscapes.
Unacceptable to me. At least that is how I remember his mantra.

Nothing brings this all home quicker than using a 4x5 or larger ground
glass focused camera. While under the dark cloth with a loupe, checking
focus, normal lens (120mm - 180mm on a 4x5) it all becomes very simple.
Focus on a distant object (mountain or whatever) and no matter how much you
stop down, even f/64, things close in front of you are not going to be in
focus. Focus on the things close in front of you, and the mountains will
never come into focus, even at f/64. The loupe doesn't lie! But if you
change the focus while stopped down, you can find a spot where both the
close and the distant are in focus. It is actually much closer than 1/3rd
the way into the scene. When infinity is involved, the 1/3-2/3 rule isn't
completely accurate. But the correct focus spot is no where near
[Merklinger's] infinity (that distant mountain or whatever).

The nice thing about LF is that all of this is directly observable. No
formulas or hyperfocal cards needed. Just a loupe and a dark cloth. And
with a little lens or film tilt, you can override the simple DOF rules with
Mr. Scheimpflug's rules.

By doing this over the years, it gives one insight as to where to focus
when using a camera where DOF is not directly observable, such as the M Leica.

Jim