Archived posting to the Leica Users Group, 2003/07/21

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Subject: Re: [Leica] Focussing Noctilux and 75 Summulix in low light
From: Karen Nakamura <mail@gpsy.com>
Date: Mon, 21 Jul 2003 15:38:56 -0500
References: <BDCCDB99-BBB6-11D7-87FE-000393AC0E1A@johnbrownlow.com>

Remember that with rangefinders, you can have what I call "RF 
parallax error" at close distances.

If you imagine that the RF window, the lens, and the object being 
photographed make a triangle:

rf
*\
|   ---------------
|                          ----------------------------
*-------------------------------------------*
lens                                                              object

You can see that the  lens-object distance will be shorter than the 
rf-object distance. This is mainly a problem in lens testing, because 
most of us  place that ruler coplanar with the lens.

With 3D objects such as faces or brick walls (or peeling paint), this 
isn't a problem. But it is a problem anytime you try a small object 
at very close distances.   Try putting the object so that it forms an 
equilateral triangle between the lens and rangefinder.

I ran into this when testing my russian lenses against Dante's hypothesis....


Karen Nakamura
http://www.photoethnography.com

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In reply to: Message from Johnny Deadman <lists@johnbrownlow.com> (Re: [Leica] Focussing Noctilux and 75 Summulix in low light)