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Understanding Auto Focus Modes and Auto Focus Lens

written by: AlyssaAst•edited by: Rhonda Callow•updated: 9/14/2009

An auto focus lens often makes photography much easier. Auto focus modes on cameras are a great thing to have on a digital camera. Despite how easy using an auto focus lens can be, understanding auto focus modes is often more difficult.

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    Auto Focus

    “Digital Camera 1” By Porah
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    What is Auto Focus?

    Auto focus modes are a quality most digital cameras have. This can really save time when taking pictures. Auto focus is often used to improve the quality of photographs. An auto focus lens automatically focuses the lens on the camera to provide the clearest and sharpest possible image to be taken. The lens will move in and out until it finds the best position for the lens to take the picture.

    There are two different types of auto focus a camera can have. The two types of auto focus are active and passive. Some cameras may have one form or the other, but expensive cameras often have both forms of auto focus. Some cameras have interchangeable lenses that can be used to switch back and forth from active and passive auto focus.

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    Active Auto Focus

    When understanding auto focus, it is important to know the difference between passive and active. Active auto focus on cameras use infrared signals to produce the image. This form of auto focus is great to use on objects within twenty feet of the camera.

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    Passive Auto Focus

    Passive auto focus is mainly found on single-lens reflux (SLR) cameras. This form of auto focus uses computer analysis within the camera to focus the lens. Passive auto focus has no distance limitations on its ability to focus on an object, whereas active auto focus does have limitations.

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    Auto Focus

    Although auto focus can make the picture taking process easier by quickly focusing on an object, there are some down sides to using this feature. An auto focus lens can focus on the wrong object. It can sometimes focus on an object in the background instead of the intended object. It is important to not rely on auto focus alone, and to make sure you double check the image before pressing the shutter button.

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    How to Use Auto Focus

    When using auto focus cameras, they can often focus on the wrong object. If you are trying to photograph a couple in front of a landscape the camera often makes this mistake. If the couple is placed in the center of the photo, the auto focus will go in between the people and focus on the landscape behind them. To solve this problem, there is a tip you can use.

    To keep the auto focus lens from focusing in between the couple, move the couple to either the right side of the photo or the left. Keep the auto focus brackets in the center of the image and press the shutter button. This is a great way to take pictures of people with landscapes when using an auto focus camera.

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    References:

    “Auto Focus Systems” Auto Focus

    “Understanding Auto Focus” Practical Photography by John Freeman

    Photo: “Digital Camera 1” By Porah Stock.xchng