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Phase detection AF explained
#1

This is an awesome primer from dpreview about how most AF systems work, and the difference between phase detection (used my most DSLRs) and contrast detection (used by most compacts).

Quote:All current compact and mirrorless cameras use contrast detection AF, where the lens is racked back and forwards until the camera finds the position that gives the greatest contrast (which signifies being in focus). Their lenses tend to be designed with very light focusing elements that are fast to move so that this process of trial-and-error can be conducted as quickly as possible. Intelligent processing also attempts to minimize the need to hunt too far for focus but there is still some hunting to be done.
As opposed to phase detection which captures light from different parts of the lens so that the images can be compared to see how "out of focus" they are. (The diagrams in the articles really help for this explanation). Most DSLRs use a dedicated AF sensor behind the mirror (which is slightly opaque) which splits the light using prisms so that can capture light from different parts of the lens.

Most compacts however don't have this additional sensor - but apparently Fujifilm has announced that their new Fujifilm F300 EXR and Z800 EXR compacts have a specially designed sensor that allows for through the lens phase detection, enabling focus times as fast as 0.158 sec.

http://www.dpreview.com/news/1008/100805...filmpd.asp
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#2

Technology leaves our only 4 years old cameras so behind.

Thanks for the link Jules... Smile

A work of art which did not begin in emotion is not art.
Paul Cezanne
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