Archived posting to the Leica Users Group, 2003/02/14

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Subject: Re: [Leica] Re: Hexar RF Back focus one more time
From: Henning Wulff <henningw@archiphoto.com>
Date: Fri, 14 Feb 2003 12:56:55 -0800
References: <200302131714.JAA11678@mejac.palo-alto.ca.us> <a05111700ba71d2acb52f@[218.102.82.212]> <00fb01c2d3d8$e7153a80$6f01a8c0@jsbigrig> <008401c2d44e$ce94efc0$2dd871d8@jbilinsk>

At 9:30 AM -0800 2/14/03, Jacques Bilinski & Barbara Bradbury wrote:
>  > I'm sure this has been covered but why would you test a lenses/bodys focus
>>  using a wide angle @ infinity? Wouldn't you want to use a tele @ the
>minimum
>>  focusing distance ???????????????????????????????????????????
>>
>
>You want to do the test at infinity rather than a close focus distance in
>order to test the lens/body compatibility independantly of the rangefinder
>adjustments. Rangefinders in RF cameras easily get out of adjustment if the
>camera is banged, and this won't play a part in the test if you do it at
>infinity.
>
>You want the widest aperature lens you have in order to minimise the depth
>of focus (i.e. depth of field inside the camera at the film plane).
>
>Focal length doesn't matter, contarary to what is often written on this
>list.  Best lens for this test is a Noctlux.

Focal length can make the test easier because if the flange - film 
distance is 1mm too large, the lens will be focussed at a shorter 
distance; with a wide angle lens this distance will be significantly 
closer to the camera than with a longer focal length lens, and thus 
the discrepancy will show up. As I mentioned before, if the 
discrepancy between the Hexar and the Leica bodies is as large as 
some have said, a 35 lens would focus at about 6m instead of 
infinity. A Summilux wide open would show this discrepancy easily. A 
Noctilux would focus at about 12m with the same film - flange 
discrepancy; that is why it is easier to see with a wideangle lens.

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    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:henningw@archiphoto.com
  |[ ]|     http://www.archiphoto.com
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Replies: Reply from "Jacques Bilinski & Barbara Bradbury" <jbilin@axionet.com> (Re: [Leica] Re: Hexar RF Back focus one more time)
Reply from Jerry Lehrer <jerryleh@pacbell.net> (Re: [Leica] Re: Hexar RF Back focus one more time)
In reply to: Message from Cummer <cummer@netvigator.com> ([Leica] Re: Hexar RF Back focus one more time)
Message from "John Straus" <Mail@SlideOne.com> (Re: [Leica] Re: Hexar RF Back focus one more time)
Message from "Jacques Bilinski & Barbara Bradbury" <jbilin@axionet.com> (Re: [Leica] Re: Hexar RF Back focus one more time)