Archived posting to the Leica Users Group, 1999/03/25

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Subject: [Leica] Re: Digest V7 #91 - Leica R (extension tubes)
From: "John P. Koch" <jpkoch@telerama.lm.com>
Date: Thu, 25 Mar 1999 23:02:43 -0500

To:  John Gong <jgong@cisco.com>

No, Terry IS referring to an extension tube.  You are correct in stating that an
extension tube
generally is used for macro photography.  What Moose Peterson has done, as well as
many
wildlife photographers, is to use an extension tube on a long telephoto to decrease
the minimum
focus range of the long telephoto.  This does allow you to come in closer to the
subject in the
field and essentially "magnify" the image on the film.  Just as in macro
photography, as you
state.  But what this also does is to separate the subject from the background as
well.  You maintain
that same narrow depth of field demonstrated by a 400  @ f2.8 or 500mm @ f4.0, etc,
but since the
subject is so much closer, the background is even further away.  The result is a
wonderfully
"blown away" background.

<snip>
I really don't understand this proposal.  An extension tube physically
moves the lens outboard from the body.  The intent is for macrophotography,
as the focus point moves such that close focus is possible, but at the
disadvantage of losing distant focus.  If your intent is to photograph
wildlife other than insects at close range, I'm afraid an extension tube is
not what you need.  Your extenders are intended to permit an increase in
effective focal length  and preserving your focus range on a lens.  Are you
sure this isn't what Moose used instead?  With the increase of focal
length, shortened depth of field results in nice blurred backgrounds.
<snip>