Archived posting to the Leica Users Group, 2003/01/14

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Subject: Re: [Leica] Useful link for focus adjustment
From: Henning Wulff <henningw@archiphoto.com>
Date: Tue, 14 Jan 2003 10:24:45 -0800
References: <C22AC812-27CB-11D7-9151-0050E42E6E0B@shaw.ca> <004901c2bbe0$a5bc3a80$388a8418@symkeehx5nw8g8>

At 4:21 PM +0100 1/14/03, animal wrote:
>  > Whoa Totally twisted! It looks like a great deal of unnecessary fun.
>>  All you have to do is focus normally and then slide the camera sideways
>>  to the composition you are after*. Some lenses have a curved field and
>>  then just rotating the camera is the best way.  No fuss, no muss and no
>>  stress marks.
>>
>Does a curved field mean that it is circular i.e that no matter at what
>angle, the subject would remain in focus?
>simon jessurun

Not likely, but in rare circumstances, yes.

Field curvature can take different shapes and degrees, and besides 
varying by lens also varies by focussed distance (and focal length, 
in zooms). Most fast lenses display fairly significant field 
curvature at closer distances, so trying to apply the complex 
trigonometric calculations based on a lens having a perfectly flat 
field like Martin Tai does is largely pointless. In 35mm generally 
only macro lenses have as one of their design goals a flat field, and 
even there it is not perfect.

The good thing about field curvature in relation to this discussion 
is that the imaged field is usually concave as seen from the camera.

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    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:henningw@archiphoto.com
  |[ ]|     http://www.archiphoto.com
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In reply to: Message from John Collier <jbcollier@shaw.ca> (Re: [Leica] Useful link for focus adjustment)
Message from "animal" <s.jessurun95@chello.nl> (Re: [Leica] Useful link for focus adjustment)