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For a thin lens with a known aperture and working for an object at a given position, calculates the distance from the front focal plane to the object, the distance from the lens to the image, the distance from the back focal plane to the image, the magnification, the numerical aperture in the object space and the numerical aperture in the image space as functions of the back focal length, the distance from the lens to the object and the aperture diameter (the aperture is coinciding with the lens).