Color picture tube

A color picture tube, comprising:

• a panel;
• a phosphor screen in a substantially rectangular shape, formed on an inner surface of the panel;
• and
• a shadow mask in which a number of electron beam passage apertures are formed, placed so as to be opposed to the phosphor screen,
• wherein a radius of curvature of an outer surface of the panel is 10,000 mm or more,
• the shadow mask is made of a material containing 95% or more of iron,
• assuming that a distance from a reference point to a useful area end on the inner surface of the panel in a direction vertical to a tube axis is L′, and a sagging amount at the useful area end with respect to the reference point in a tube axis direction is Ze′, in a case of defining a first sagging amount curve representing a first sagging amount Z1′ at a point at a distance d′ from the reference point in the direction vertical to the tube axis, represented by the following Formula 1′, and a second sagging amount curve representing a second sagging amount Z2′ at a point at the distance d′ from the reference point in the direction vertical to the tube axis, represented by the following Formula 2′,
• a sagging amount change curve along a curve C1′ on the inner surface of the panel, which a plane passing through a center P0′ of a useful area of the panel and parallel to the tube axis and a major axis crosses, satisfies the following Condition 1′, and
• assuming that an intersection between the curve C1′ and the useful area end of the inner surface of the panel is a major axis end PL′, a distance from the center P0′ to the major axis end PL′ along the major axis is W′, and a point on the curve C1′ away from the center P0′ by ⅔×W′ in a major axis direction is P1′, a sagging amount change curve along a curve C2′ on the inner surface of the panel, which a plane passing through the point P1′ and parallel to the tube axis and a minor axis crosses, satisfy the following Conditions 2′:
• Z1′={(Ze′·(1−rf1′))/L′2}d′2+{(Ze′·rf1′)/L′4}·d′4 Formula 1′:
• Z2′={(Ze′·(1−rf2′))/L′2}d′2+{(Ze′·rf2′)/L′4}·d4 Formula 2′:
• Condition 1′:
• Assuming that a sagging amount at the major axis end PL′ with respect to the center P0′ is ZPL′, at least 60% portion of the sagging amount change curve along the curve C1′ between the center P0′ and the major axis end PL′ is present between the first sagging amount curve represented by the Formula 1′ and the second sagging amount curve represented by the Formula 2′, where L′=W′, Ze′=ZPL′, rf1′=0.7, rf2′=1.2,
• Condition 2′:
• Assuming that an intersection between the curve C2′ and the useful area end of the inner surface of the panel is P2′, a distance from the point P1′ to the point P2′ in a minor axis direction is H2′, and a sagging amount at the point P2′ with respect to the point P1′ is ZP2′, at least 60% portion of the sagging amount change curve along the curve C2′ between the point P1′ and the point P2′ is present between the first sagging amount curve represented by the Formula 1′ and the second sagging amount curve represented by the Formula 2′, where L′=H2′, Ze′=ZP2′, rf1′=−0.4, rf2′=0.