let\'s imagine a situation where we have a person standing and a lens ~ 6 feet away from them. We want to focus to a point on their face. We\'ll call this point A. The camera is located at point B.
The composition calls for point the camera lens at the person\'s neck. If we were to extend a line perpendicular to the film plane, straight through the lens in the person and then extend a line parallel to the film plane through the point we want to focus, these lines would intersect at point C. Point C is where we would want to focus in order to render point A (the face) in focus.
AB, BC, AC is a right triangle. Thus, given the Pythagorean theorem, we know that the distance from A to B (camera to face) is longer than the distance from B to C. So, if we focus at point A (the face) but recompose to point the camera at point C, we will have effectively focused behind the point of best focus to render the face in focus.
Thus, I can effectively show why focus -> recompose isn\'t a good method to use (mathematically to boot!).
Marty Bingham wrote:
Let\'s move on please.
Marty
Oops. Sorry, didn\'t read this until after my post. Well, Math is my first name (seriously!).
Feb 09, 2010 at 09:41 PM
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