Re: [Leica] M-focus procedure

[Jim Brick <jim@brick.org>]

Don,

Assuming that your camera and lens are OK, focusing is both simple, and
complicated. Aligning the rangefinder images is simple. It should "snap in"
when they align perfectly. But focusing with a 90mm lens is somewhat more
complicated. Depth of field is quite shallow. Depth of field, for any lens,
covers 1/3 in front of where you focused and 2/3 behind. And the distance
forward and behind follow hyperfocal theory for the lens & f/stop used. So
if you are taking a portrait, and you focus on the persons ears, there's a
very good chance that the eye's will be out of focus. Almost guaranteed
that the nose will be out of focus. It's called backfocus. Focus is very
tricky when it comes to shallow DOF. You should focus either exactly on, or
slightly in front of, the exact thing you want to be in critical focus. For
a portrait (face on) focusing on the eyebrows will put the most important
part, the eyes, in focus. Depending on the f/stop, you will have a good
chance of having both the nose and ears in focus. With longer lenses and
wide f/stops, focusing takes a lot of thought and intuition. Practice
practice practice.

Starting on page 76 of Jonathan Eastland's "Leica M Compendium" ISBN
1-897802-05-6, is a good discussion of focusing and depth of field.

Of course, "The Leica Manual, 15th Edition" ISBN 0-871000-03-2, has the
best description of focus and focus theory. Page 508 describes exactly what
I said above. A 50/2 Summicron set at f/2 and focused at 20 feet, will have
a sharp DOF from 15.5 feet to 28.2 feet in focus. That's 4.5 feet in front
of the plane of focus and 8.2 feet behind the plane of focus. The plane of
focus was 20 feet. Approximately 1/3 forward and 2/3 behind. Watchword
about focus... never ever back focus. It makes lousy photographs.

When you are going to take a photograph, stop and think about what you want
in focus. Then stop and think about where you have to focus, in order to
get what you want in focus... in focus.

Hope this helps.

Jim

ps... Focusing and effective use of DOF is one of the most difficult
photographic techniques to master. Once mastered, it becomes intuitive.


At 08:53 PM 7/5/98 -0400, you wrote:
>Shot a few rolls this weekend, using my M6
>and several lenses, but mostly a 90mm.
>My in-focus average was NOT good.
>
>This is probably the king of FAQ, but refresh
>my memory.  Do you focus the M6:
>
>1. Starting with the lens at near focus, moving out
>                  or
>2. starting with the lens at infinity, moving in?
>
>I'm wondering if I'm just doing it wrong?  I have
>been using method #1 (start closer than needed)
>
>Showing my Leica green-ness...
>don ferrario
>