Premium Member Laurent Andrieux Posted February 25, 2005 Premium Member Share Posted February 25, 2005 The focal length is, by definition, the distance from the lens (considering a thin lens) at wich the image of an object placed at the infinity will be sharp. The focal length is then only depending on the lens carachteristics. According to the size of the lens and mount, one lens will fit a camera and format, or not. The format of the image is given by the aperture plate of the camera (film) or the usefull dimension of the pick-up device (video) The field of view can be given in 2 different ways : 1) Object size : at a given distance, the frame will cover a certain height and a certain width. It depends on the focal length and the image size, wich is given by the format. The relationship is therefore : DXI = OXF where D is distance from camera to subject, I is the image size, O is the object siez or covered Width/heigth at the given distance D, and F the focal length. 2) Angle of view : if you consider A the angle of view, then, tan(A/2) = I/2F where I is the image size, either height or width and F the focal length. so, when you have I and F, calculate I/2f = tan(A/2), let's say, the result is R, make sure your calculator is in degrees, compute tan^-1 ® or INV tan ® according to your calculator as to have the inverse function of tan , then you get A/2, multiply by 2 and you get A In another post, I'll give you the common image sizes for different common film and video formats Quote Link to comment Share on other sites More sharing options...
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