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Old Jul 9, 2003, 6:48 AM   #1
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Default AUTOfocus problems?

something i never knew before but read the other day; is that apparently autofocus works best when the centre of the focus area is pointed at an area with some definable contrast, i.e. an area of the frame which has some light and dark patches next to each other; the more contrast the better.
I never experimented with this before, but as soon as I did i noticed an improvement in auto focus, including in low light some of the time.
If there isnt any distinct difference between any areas of lighting and there arent any clearly defined lines within the LCD frame or the viewfinder, then you can look for somewhere at about the same distance which does > and lock the focus then re-compose and shoot.

Im only a 1 year old in photo years, so maybe everyone else already knows this. Is defining lines of contrast - how autofocus works?
Anyway Im interested, does this tip work for others as well as it does for me?
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Old Jul 9, 2003, 8:26 PM   #2
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Hi. Yes what you say is very true,and i also use the auto focus the same way you do. The more contrast the better. This is what i find with the nikons i have. Tealblue
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Old Jul 10, 2003, 3:55 AM   #3
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Default Re: AUTOfocus problems?

Quote:
Originally Posted by dom277
apparently autofocus works best when the centre of the focus area is pointed at an area with some definable contrast, i.e. an area of the frame which has some light and dark patches next to each other; the more contrast the better.
If there isnt any distinct difference between any areas of lighting and there arent any clearly defined lines within the LCD frame or the viewfinder, then you can look for somewhere at about the same distance which does > and lock the focus then re-compose and shoot.
You are absolutely right. Nikon Coolpix cameras use the so-called contrast-detection method for auto-focusing. Its concept is very simple and is based on an almost obvious fast: the image is in focus if its contrast is the highest of all possible (other) images. Thus, as you have observed, if the area being focused on has contrast, the camera can lock on the subject quickly. The "hunting" is basically due to low contrast (or even no contrast). Of course, low light implies low contrast. :lol:

CK
http://www.cs.mtu.edu/~shene/DigiCam
Nikon Coolpix 950/990/995/2500/4500 user guide
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