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06-01-2014, 07:36 PM   #1
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K30 autofocus system: phase detection vs contrast detection

Hi people,

Am bit confused with the autofocus system in K30 in regards to phase detection and contrast detection. As per various articles, live view uses contrast detection and the normal mode is phase detection if we are using the view finder. For night mode or low light situations, contrast detection is better as per the reviews but I really hate to use the live view. So how is the autofocus system is used based on whether you use view finder or live view?

Also I use focus select mode to choose my focus point so that i can focus on the eye of the subject during portrait. Does the cross type points will have mode advantage than the other two points for focus or they are all the same? Apologies for the noob question since am still trying to understand the autofocus capability of K30.

Regards,
Jai

06-01-2014, 09:32 PM   #2
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Phase detection is done via a separate sensor in the body. When the mirror is flipped up for live view, neither the exposure meter nor the autofocus sensor can "see" anymore. Thus the camera must rely entirely on what the main sensor sees to determine focus (via contrast) and exposure.

"Cross" type focus points can detect both horizontal and vertical edges to focus on. Non-cross types can only detect edges in one direction (horizontal or vertical).
06-01-2014, 10:46 PM   #3
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Thanks Jim. In K30 which ones are the cross type focus points?
06-01-2014, 11:05 PM   #4
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QuoteOriginally posted by jaikumarr18 Quote
Thanks Jim. In K30 which ones are the cross type focus points?
You're welcome. The nine central points are cross type. The outer two are not.

06-01-2014, 11:22 PM - 1 Like   #5
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QuoteOriginally posted by jaikumarr18 Quote
Also I use focus select mode to choose my focus point so that i can focus on the eye of the subject during portrait.
One quick suggestion:

By far the easiest and quickest way to use autofocus is to use only the center point. For portraits, you focus on the eye using the center point, keep the button half pressed to lock focus while you recompose the shot, then finish by pressing the button all the way.

Even better is to use back button focus in combination with AF.C mode (still with only the center focus point), but that's just a more advanced application of the same technique. I'd hold off on learning that until you're comfortable with the above method.

The only time where selectable focus points make sense is when the camera is on a tripod. In that situation I'm manually focusing anyway, so I never even use selectable focus points. But, they do minimize the hassle of recomposing on a tripod with autofocus.
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