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Re: [OM] Eeeek!

Subject: Re: [OM] Eeeek!
From: "Carlos J. Santisteban" <zuiko21@xxxxxxxxx>
Date: Sat, 11 Aug 2012 15:56:36 +0200
Hi Moose and all,


From: Moose <olymoose@xxxxxxxxx>

>but where it's CDAF will focus in a complex, 3D subject is just 'different'

>than with Canon PDAF.

>

>Example: A bee on the dark center of a sunflower. With the Canons,

>centering the central focus point on the bee would focus on the bee.

>The OM-D and 14-150 focused on the surface of the flower.


The great difference between both AF systems is that PDAF, much like a
human with a split-screen, usually "knows" if a particular object within
the AF area is in focus, back-focused or front-focused. It seems they're
designed to focus on the closest object inside the AF area, leaving the
rest beyond the focus plane.


On the other hand, CDAF (which works more like a matte screen) has no idea
at all -- it just moves the focusing mechanism back and forth and keeps
comparing the apparent sharpness of whatever lies on the AF area. If the
measured sharpness/contrast is going _down_, it reverses the focusing
direction, until contrast goes down again -- supposedly after reaching the
focus point.


But if the objects inside the AF area are located at different distances,
the one who contributes "more" to that perceived sharpness (be it because
of contrast, pattern, colour, orientation... whatever) will "win" the CDAF
quest...


Cheers,
-- 
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
-- 
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