Archived posting to the Leica Users Group, 1998/01/31

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Subject: Re: [Leica] Re: Distortion
From: dannyg1 <dannyg1@IDT.NET>
Date: Sun, 01 Feb 1998 03:54:07 +0000

Hey Mike,

You took my line! 

It's called 'oblique pespective distortion' and is exaggerated by the wider field of view 
specs of most RF lenses. As any lens is positioned closer to the film plane, it naturally 
requires a wider field of view to cover (than one situated farther away) than an 
equivalent SLR version would. Because our eyes have a distinct field of view, wider 
ones create more OPD than were used to. Though our eyes have a specific focal 
length, the effect applies to any focal length (or most any) as we recognize any 
divergence from the norm, irregardless of focal length. Of course, many longer RF 
lenses (anything 50 and above) can be designed to sit, rear element as far foward as 
equivalent SLR version, but, not all are designed that way.

OPD give rangefinder cameras a different looking rendition than SLR's and, as I 
wrote on CIS so long ago, it is part and parcel to working within the genre of street 
photography (and some others). 

Another effect that has far more visual confusion than most give credit to is the 
'telephoto effect', which is related to OPD in the sense that it artificially compresses 
the perspective, counter to a more normal rendition a long focus version would. Pull 
out your mirror lenses and have a look for yourselves. The DOF and persective 
rendition will look closer to what you might expect with a 1000mm, even though 
you're shooting at 350-500mm.

Danny Gonzalez
Danny Gonzalez