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

[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]

Subject: RE: [Leica] Focusing Noctilux and 75 Summilux in low light
From: "Don Dory" <dorysrus@mindspring.com>
Date: Mon, 21 Jul 2003 20:20:07 -0400

John,
AF to some extant depends on some purely mechanical settings that can
cause misfocus.  We all know that an SLR depends on the distance to the
film plane be matched to the distance to the ground glass screen by way
of a mirror.  However, the AF mechanism depends on a sub-mirror that
bounces the light onto the AF sensors.  Very small movements
(temperature expansion for example) can affect the accuracy of the auto
focus.  

A real world example would be a SLR that has received hard use
occasionally needs the mirror reset to the proper angle.  In the old
days there was a fixed stud that caught the mirror at the correct
position.

Not discussed here, but the budget SLR's especially have pretty wide
tolerances for auto focus as the AF sensor is in plastic which does move
enough.  But hey, nobody uses an 85 F1.2 on such a body.

0.02

Don
dorysrus@mindspring.com



On Monday, July 21, 2003, at 03:31 PM, George Lottermoser wrote:


John wrote in part:
- - For poorly lit or low contrast subjects on medium lenses, the RF wins 
for me.

- - For poorly lit subjects at close distance, the AF is generally more 
accurate unless you have really calibrated your RF as described above.

- - For lenses 75mm and greater, especially wide open or in poor light, 
AF is better than RF but MF on an SLR is better than both of them.

Those are my personal prejudices. The probably don't reflect anyone 
else's experience.


- --
John Brownlow

http://www.pinkheadedbug.com
http://www.unintended-consequences.com

- --
To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html


- --
To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html