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Old April 28th, 2006, 10:57 AM   #1
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Understanding Infinity Focus

Am I right in my understanding that infinity focus is the point of your image where everthing beyond will be in sharp focus without any further adjustment, or am I totally wrong?
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Old April 28th, 2006, 11:34 AM   #2
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Quote:
Originally Posted by Aviv Hallale
Am I right in my understanding that infinity focus is the point of your image where everthing beyond will be in sharp focus without any further adjustment, or am I totally wrong?
Lenses have a plane of sharp focus and everything on either side of the plane is out of focus to a greater or lesser degree. The zone of acceptable focus, the range between which the degree of out of foucus is smaller than the eye can resolve is called the "depth of focus" - sometimes erroneously called the "depth of field." When you look at a distant mountain range, comparatively speaking that might as well be on the edge of the universe and when the lens is a such a distance from the sensor or the film that its plane of sharpest focus coincides with the plane perpendicular to the horizon, it is said to be at infinity focus. Everything beyond that point is sharp and things extending for a certain distance this side of the horizon will also be in apparent focus. The distance that will appear sharp depends on the diaphram setting or the iris. The smaller the iris, the greater the depth of focus.

Still camera and prime lenses have a depth of field scale engraved on the barrel. One trick is to align the infinity focus mark on the lens with the marking corresponding the the iris setting your're using. That way you have the greatest degree of sharpness extending from what distance is alongside the closer f/stop marking all the way to infinity. This is called setting the lens to its hyperfocal distance.
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