Archived posting to the Leica Users Group, 1998/02/04

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Subject: Re: [Leica] Re: Distortion
From: dannyg1 <dannyg1@IDT.NET>
Date: Thu, 05 Feb 1998 00:14:09 +0000

Henning,

In the interest of gaining a better understanding of the complex issues we're 
discussing, I wish you wouldn't be brief. I have tried to explain my points in detail 
in the interest of both, teaching something and offering to learn. 

>>
1) In an ideal (fully corrected) lens, used on flat film, perspective
rendition is the same for all lenses, no matter the construction type and
focal length. As the field of view increases, the corners of the image
relate less and less to our usual visual interpretation, and we call that
perspective distortion.
<<

I've been looking for a written proof of this for a very long time, but when Sidney 
Ray or Stroebel/Zakia write about perspective distortions, their examples are always 
entirely based on true wide angle and long focus designs; never retrofocus or 
telephoto versions.

Information about the telephoto effect is very scarce and what is available is vague 
enough to teach little of its severity (or lack of severity). This retrofocus effect I'm 
arguing is something that I (and many others) have noticed in practice. I've tried to 
explain many reasons that it can (and to my mind, does) exist. 

I realise (now at least) that you strongly disagree, but isn't your assertion (of 
perspective rendition being equal per focal length, whether emulated or not) more a 
question of interpretation of the texts than it is of a steadfast optical rule? 

Regards,
Danny Gonzalez