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John Hennessy
9-Feb-2001, 03:09
I have a question about a LF lens term. "angle of coverage" is defined in an old Calumet catalog as "the angle formed lines connecting the image nodal point to opposite sides of the image circle." This measurement is often prominently featu red is LF brochures and what not; so my question is: what is its significance? T he diameter of the image circle. focal length, aperture range, etc. seem far mor e important.

Thanks.

Pete Andrews
9-Feb-2001, 06:34
The image circle is very specific. The figure given by the lens maker is usually measured with the lens focused on infinty.Angle of coverage, on the other hand, can be used to find the radius of the image circle at any lens extension, using the tangent of the half-angle.

9-Feb-2001, 07:40
When you are trying to cover 16x20" with a 4" lens (not that I am), AOC is everything. I believe the formula you want to use to find the minimum angle of coverage for a given format is: 2*(arctan((sqrt.gif(x<sup>2</sup> + y<sup>2</sup>)/2)/F), where x is the horizontal dimension of film, y is the vertical dimension of film and F is the lens focal length. Note that these angles are the minimums required to cover the given formats and do not account for movements.