Composite shiftable aperture mask

A composite shadow mask for a cathode ray tube or the like comprising:

• a mask support frame;
• a first shadow mask made of a first material and fixedly mounted to said mask support frame, said first shadow mask having a first set of openings therein for defining the size of an electron beam passing therethrough, said first shadow mask being sufficiently thick so as to provide structural integrity but sufficiently thin so as to require structural support within said frame, said first shadow mask characterized by having a first thermal expansion rate;
• a second shadow mask made of a second material of a second thickness, said second shadow mask characterized by having a second thermal expansion rate different from said first thermal expansion rate;
• said second shadow mask sufficiently strong so as to provide structural support for both said first shadow mask and said second shadow mask with said second shadow mask shiftably mounted on said support frame to support said first shadow mask in response to changes in temperature of the shadow masks, said second shadow mask having a second set of openings in alignment with the first set of openings and sufficiently larger than said first set of openings so that when said first shadow mask and said second shadow mask shift with relation to one another due to increase or decrease in the temperature of the shadow masks the second shadow mask does not block the first set of openings in the first shadow mask, to thereby permit passage of an electron beam through the openings in both said first shadow mask and said second shadow mask, with a size of the electron beam determined by the shape and size of the openings in the first shadow mask.