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 Author
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Topic: EF kit lense Auto Focus (Read 6292 times)
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stixstudios
Newbie
Posts: 1
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Hi Guys,
My first post here.
Sorry to be a bit vague, but hopefully someone can give me an answer.
How does Auto Focus actually work?
Is it done inside the lens or camera body?
ie. Where are the brains?
I am aware that the drive is inside the lens, but where are the decisions made - and how?
Any help would be greatly appreciated.
Steve.
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KeithB
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Here is a good video by Nikon: http://www.nikon.com/about/technology/core/software/caf/Short answers: The "brains" are in the camera which drives the focusing motor in the lens in a feedback loop. It does not use the sensor (After all Autofocus pre-dates digital cameras!) If you have any expereince with feed back loops - ever tried to ride the thermostat to get a certain temperature? ever driven a slow boat with a big "dead spot" in the center of the steering? You will know that feedback loops are tricky to design and every component is a critical part of the system. One of the known tradeoffs is speed vs accuracy. The lens it self is a critical component of the loop which is why you can buy systems to help you tune *your* lens for *your* camera. SLRS use phase detection which gives a vector error measurement, so they can directly drive to the correct focus. A P&S has to move the focus once to see if the focus point is closer or farther before it "knows" which direction to drive the motor. |
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emanresu
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Cool article, Keith. Now I am wondering if Canon IS works the same way as Nikon VR?
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Bob Atkins
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VR and IS (and OS and VC) all work in the same way. Gyro sensors detect angular rotation of the lens and feed a signal to actuators in the lens which move a small group of lens elements by the right amount calculated to compensate for any image shift. The "smarts" are built into the lens itself.
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