A new version of the theory of the nanofocusing of synchrotron radiation (SR) into nanometer transverse size using a long compound refractive lens (CRL) is developed, which adequately takes into account the aperture over the entire length of the CRL within the framework of geometrical optics, fully compatible with the theory based on the CRL propagator. For hard SR, absorption no longer completely limits the CRL aperture and taking into account the real aperture is important to obtain reliable information about the size of the SR beam at the focus. The new theory is almost analytical and allows one to determine the rocking curve of a long CRL with good accuracy, and also gives an answer in those exotic cases where standard numerical methods are not applicable.