Quote Originally Posted by Jim Jones View Post
To further complicate the discussion, in a flat film camera, a pinhole of optimum size for the center of the image is too small for the corners of the image. Also, the corners exhibit astigmatism. For the curved film "Oatmeal box" camera, the pinhole can be made slightly elliptical to improve edge performance. Even something as simple as a pinhole camera can become awfully complicated.
This is because the focal length is measured in a straight line from the pinhole to the center of the image plane, and in online calculators that is what the pinhole diameter is optimized for, correct? And the corners of the image plane are further away from the pinhole than the center is.