This is summarized from Thom Hogans's D200 manual. Light goes through
the semi-silvered mirror and is bounced down toward the bottom of the
mirror box where the focus sensors live. Before it gets there it is
split by what is called a separator lens which I suspect is sort of
like a prism in a range finder. This splits the light into two
distinct images and the line sensor underneath measures the distance
between them. If focus is in front of your subject image lines will
be closer together than expected and if focus is in back of the
subject the image lines will be farther apart. A calculation is made
about how far to move the lens so that the lines are the correct
distance apart to be in focus and lens is moved.
Winsor
Long Beach, California, USA
On Nov 9, 2006, at 3:46 PM, Wayne Harridge wrote:
>
>
>
>
>
>> Winsor Crosby <wincros@xxxxxxxxxxx> wrote:
>>
>>
>> Nikon uses a phase detection focusing system.
>>
>
> Phase of what ?
>
> ...Wayne
>
> Wayne Harridge
>
> http://lrh.structuregraphs.com
>
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