The axial shadow pattern in a crystal containing prismatic and sliding dislocation loops is investigated within the scope of the classical scattering theory. The case, when the characteristic size of distortions’ correlation in a crystal is much more than distance of shadow-picture formation, is considered. The value of a minimal output of the particles, which are scattered by the distorted chain of atoms at not too large deformations, is proportional to the concentration of defects. In addition, it is a function of the angles determining an orientation of direction of a shadow-picture observation relative to a normal to the plane of dislocation loop as well as to a Burgers vector. Therefore, angular dependences for prismatic and sliding loops differ from each other substantially. That allows using a shadow effect for diagnostics of dislocation loops in crystals.