OPTICAL SYSTEM FOR PROJECTION TYPE TELEVISION

摘要

PURPOSE:To improve focus performance at the center and peripheral part of a screen by making a fluorescent which constitutes the tube surface of an image receiving tube aspherical in a direction where the curvature of field of a projection image on the screen is corrected. CONSTITUTION:An optical system is so constituted as to obtain the best performance when a raster of 4.5 inches in length on the fluorescent surface 5 of the cathode-ray tube is expanded on the screen 6 by 10 times. The projection distance from the 1st lens 7 to the screen 6 is 700mm and corresponds to about 40 deg. in terms of an angle of a field angle, which is wider than before. The 1st lens 7 is aspherical so as to remove a spherical aberration based on the diameter and uses a glass lens so as to reduce a focus drift originating from the temperature variation of the 2nd lens 8, and the power is made as large as possible. The 3rd lens 9 has a spherical structure so as to remove a comatic aberration of high degree and astigmatism and the power is made as small as possible. The 4th lens 10 uses a concave meniscus lens of glass so as to withstand heat generated by the cathode-ray tube.