Deflection defocusing effects in cathode-ray tubes at large deflection angles

In modern color television tubes, an array of three electron beams, converging at a target, is deflected through angles of up to 55°. The conventional, small-angle deflection theory cannot be extended to deal with the convergence defects of deflection fields at such large angles since certain series expansions, basic to that theory, diverge at angles larger than 45°. A new approach to the theoretical treatment of deflection defocusing effects in cathode-ray tubes, based on the application of the theory of "focusing fields with arbitrary curved optical axes" leads to a quantitative description of deflection defects at any angle of deflection. Deflection astigmatism and curvature of field will appear in this approach as paraxial effects, while deflection coma will be identified as a second-order aberration. The mathematical treatment presented, here is suitable for numerical evaluation of deflection fields and their defects with the aid of computers.