Projection lens unit
A projection lens unit includes a main body; a lens fixed to the main body; and a hood disposed to one end of the main body close to a screen. The hood defines the outermost boundary of a view angle stretching with respect to the center of the lens and includes a light-shielding plate and a light-shielding barrel. When the shielding height of the light-shielding plate and the length of the light-shielding barrel are respectively represented by H and L, the shielding height H and the length L are set so as to satisfy the equation tan(α/2)=H/L, in relation to the view angle α. More particularly, these dimensions are set so as to satisfy the condition that the ratio H/L lies in a range from 0.74 to 0.94. The inner surface of the light-shielding barrel is subjected to surface treatment so as to absorb unnecessary light thereby, reflect it thereat, or scatter it thereat. To be more specific, the light-shielding barrel has scattering grooves disposed on the inner surface thereof.
1. A projection lens unit comprising:
a main body extending from an image receiving end to an image emitting end;
at least one lens fixed within said main body and defining an optical axis, said one lens projecting an image outward from said main body through a viewing angle having a vertex at the center of said one lens; and
a hood comprising a light-shielding barrel and an annular light-shielding plate;
wherein said annular light-shielding plate extends radially inward from an inner surface of said main body so as to lie along a plane orthogonal to the optical axis;
wherein said light-shielding barrel extends from said light-shielding plate to said image emitting end and serves to define an outermost boundary of the viewing angle; and
wherein said annular light-shielding plate has a radial dimension H, said light-shielding barrel has a length L, parallel to the optical axis, and wherein H/L is within a range from 0.74 to 0.921.
2. The projection lens unit according to claim 1 wherein said annular light-shielding plate radially overlaps a peripheral portion of a second lens mounted within said main body, between said one lens and said image emitting end.
3. A projection lens unit comprising:
a main body extending from an image receiving end to an image emitting end;
at least one lens fixed within said main body and defining an optical axis, said one lens projecting an image outward from said main body through a viewing angle α having a vertex at the center of said one lens; and
a hood comprising a light-shielding barrel and an annular light-shielding plate;
wherein said annular light-shielding plate extends radially inward a distance H from an inner surface of said main body so as to lie along a plane orthogonal to the optical axis;
wherein said light-shielding barrel extends a distance L from said light-shielding plate to said image emitting end and serves to define an outermost boundary of the viewing angle; and
wherein H/L=tan(α/2).
4. The projection lens unit according to claim 3 , wherein the ratio H/L is within a range from 0.74 to 0.94.