Archived posting to the Leica Users Group, 2000/05/17

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Subject: [Leica] Re: Re: AF
From: Jim Brick <>
Date: Wed, 17 May 2000 08:25:28 -0700

As an engineer, and currently (at this very moment) working on autofocus
algorithms and having to, via light sensors, read some portion of an image
and attempt to focus there via mathematical algorithm, I can attest to the
fact that AF will not and can not focus on "anything" you choose to have it
focus on. It does not have human cognitive powers. It therefore cannot
recognize when a specific part of a flat plain, smooth surface, or as I
said before, verticals or horizontals depending upon which way the
autofocus sensor is positioned, is in focus.

Pete, if you know how to make AF focus on otherwise unfocusable areas,
please call me. We all need to get together for lunch one of these days anyway.

Funny story... When the Contax MF autofocus camera came out, I was in KSP.
The manager was showing me how all of the features worked. I pointed it at
a Plexiglass magazine holder - side view - (it holds View Camera magazine)
and pushed the button. The camera focus started hunting... I thought it was
going to work itself into a lather. We could never get it to focus on the
Plexiglass rack. Of course it was quite simple manually. You could focus on
any part of the edge of the Plexiglass that you wished. Totally impossible
with AF. To be fare, these cameras are mostly sold to wedding photographers
and are not used for product photography while in the AF mode.


At 05:16 AM 5/17/00 -0700, Pete Su wrote:
>It is no harder to use AF to focus on a specific part of the scene than it is
>to use the leica rangefinder,  or the split image circle rangefinder on a
>focusing screen to achieve the same thing. You tell the camera to use just the
>single center AF sensor, then you use this sensor like a rangefinder. I do
>all the time with my pathetic old Nikon 8008s, and it works. It even works
>pretty well in low light, when I have a hard time confirming focus visually.
>And this is a 10 or 15 year old camera. The new sensors are a lot better.
>With SLRs, you can also confirm the focus visually, something that you
can't do
>with the Leica RF. 
>If people are going to complain about the alleged "loss of control" with an AF
>camera, then they should be worrying about exactly the same loss in the Leica

Replies: Reply from "Joe Codispoti" <> ([Leica] AF)