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What is the difference between cross type and line sens...

MotoMannequin

Livermore, CA, US
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"RE: What is the difference between cross type and line sensors?"

MotoMannequin Awarded for his extraordinary skills in landscape and wildlife photography Registered since 11th Jan 2006
Sat 25-Feb-12 03:27 PM | edited Sat 25-Feb-12 03:29 PM by MotoMannequin

If you've ever used an old split-prism focusing screen, you can think of a phase-detect AF sensor in a similar way. These will split the lines of an out-of-focus image along the split line in the prism. As you bring the image into focus, the lines converge, like this:

http://upload.wikimedia.org/wikipedia/commons/thumb/b/bf/Focus-screen-1.jpg/116px-Focus-screen-1.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/1/12/Focus-screen-2.jpg/115px-Focus-screen-2.jpg

Now, imagine trying to focus on a horizontal line using a horizontal split-prism; It can't be done. A horizontal split is great for focusing on vertical lines, ok for focusing on diagonal lines, and useless for focusing on horizontal lines. Some focusing screens are split on a diagonal line which gives ok focusing on horizontal & vertical lines, but still can't focus on any line parallel to the split.

An AF sensor can be thought of in a similar way. Non-cross sensors can't detect contrast lines parallel to the sensor. A cross-type sensor is like having 2 sensors, one horizontal and one vertical, which can detect lines in any orientation.

Larry - a Bay Area Nikonian
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A topic tagged as having a question What is the difference between cross type and line sens... [View all] , gqtuazon , Sat 25-Feb-12 11:59 AM
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