Archived posting to the Leica Users Group, 1998/07/31

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Subject: Re: [Leica] 2x extender R disappointment
From: Eric Welch <>
Date: Fri, 31 Jul 1998 19:41:30 -0500

At 09:37 PM 7/31/98 +0200, you wrote:

>Comment : remember the converter's law :when you use a 2X-extender, Apo or
>not, Leica or not, you double the size of the image and you divide by two
>the resolution of the lens.

It takes the center of the image circle, and transmits it. So your math
above doesn't add up. It certainly doesn't cut it in half. If that were
true, then the best lenses would be one element lenses, because if you add
a second one, it would cut the resolution of the first one in half, then
the third would cut it in half again. A converter just creates a different
optical configuration. It doesn't cut the quality in half.

Imagine how bad my 70-180 would be with its 13 elements. 

- -- 

Eric Welch
St. Joseph, MO

Better to understand a little than to misunderstand a lot