Re: Why is the pixel count growing so slowly?
- From: davem@xxxxxxxxx (Dave Martindale)
- Date: Wed, 16 May 2007 06:34:48 +0000 (UTC)
acl <achilleaslazarides@xxxxxxxxxxx> writes:
Actually,
the owner said something about working in contrast-detection mode - why he
had that setting I don't know.
But how can it do that if the mirror is down? What would detect the
contrast? And why would they put such a think on a camera which
already has an AF system?
Each of the SLR focus sensors is a little CCD, possibly 1D instead of
2D. In phase detection mode, you calculate the correlation of the data
from this sensor with the data from the matching sensor that captures
light from the other side of the lens, but light that is destined for
the same place in the focal plane. For contrast detection, just look
at local contrast between pixels in the same CCD. The higher the
difference, the more high frequency content, and (probably) the sharper
the image.
As for why you'd choose contrast detection instead of phase, I don't know.
Dave
.
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