Archived posting to the Leica Users Group, 1997/12/18

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Subject: Re: [Leica] Infinity focus tip
From: "Henning J. Wulff" <>
Date: Thu, 18 Dec 1997 20:48:49 -0800

Francois Jouve wrote:

>I didn't read all the messages from this thread, but it appear that most
>of you prefer focusing their wonderful lens to a finite distance, using
>depth of field to get good details at the infinity.
>Some time ago, I found on the net a very comprehensive study on the DOF.
>You'll find it together with other photographic stuff at
>The author's thesis (Harold Merklinger) is essentially the opposite:
>the only way to get the best definition at infinity (or very faraway) is
>always to focus at infinity. Besides, according to him, you can throw away
>all your DOF scales and tables. They all are bullshit for modern lenses
>and films. He also proposes a good tip to visualize the DOF, independent
>of the focal length: look at the diameter of your diaphragm. Then, once
>the lens is focused at infinity, you can resolve all details of this size
>*at any distance*.
>Have a look at it. It's sometimes technical but very interesting.

This is definitely the correct way to do it.

Also, please note that in spite of what has been posted here in recent days
about infinity as it relates to optics and photography (no need to mention
the big bang and missing dark matter for this stuff) is that it starts not
very far away. If, using a specific lens/film combination you take two
shots at a given aperture, with the lens focussed at infinity (all light
rays which are at best focus on the film plane are parallel before they
enter the lens) for one, and the lens slightly off infinity for the other,
these two shots are not distinguishable by any technique, the second point
that you focussed on is also at 'infinity' for that lens/film/aperture

If you are dealing with practical circles of confusion, infinity is closer
still. BTW, I also hardly ever believe DOF scales. For teles around 100mm,
I stop down 1 to 2 stops more for most purposes, and for wideangles of 24mm
and less, I stop down 3 stops more than the DOF scales indicate, as we are
more critical of sharpness in wideangle shots.

   *            Henning J. Wulff
  /|\      Wulff Photography & Design
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