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[OM] Re: What is backfocus?

Subject: [OM] Re: What is backfocus?
From: Wayne Harridge <wayneharridge@xxxxxxxxxxxxxxx>
Date: Fri, 22 Jun 2007 11:57:32 +1000




> Winsor Crosby <wincros@xxxxxxxxxxx> wrote:
> 
> 
> The way I understand it is that the AF system generates a double  
> image for the active focus point, just like a rangefinder, at least  
> with the phase systems like the D200. It is set up so there is never  
> a zero even at perfect focus. The distances between the double images  
> are mapped in the controlling chip to distance. So in this case the  
> camera always knows whether it is in focus or out. If the images of  
> the fence post are x microns apart the lens is focused at distance y.  
> It is more like the early rangefinders that read a distance that you  
> set on the camera by turning the focusing ring except that here the  
> controlling chip, not you, is doing it.
> 

Then the camera must need to do some sort of image recognition.  I wonder how 
it works focussing on a regular grid ?

...Wayne


Wayne Harridge

http://lrh.structuregraphs.com

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