Single-focus lens for electronic still cameras
View Patent ↗A single-focus lens for an electronic still camera is formed of at least one meniscus lens element that is placed on the object side of a stop, with at least one surface of this meniscus lens element having a curvature such that light rays that pass through the stop are incident the surface substantially normally for all field angles, and an infrared-blocking coating is provided on the surface. Preferably, two specified conditions are satisfied to ensure that rays which are incident onto the coating are not adversely affected by the coating, thereby preventing color variations of objects which otherwise would occur.
1. A single-focus lens for an electronic still camera, said single-focus lens comprising:
at least one meniscus lens element that is placed on the object side of a stop, with at least one surface of the meniscus lens element having a curvature such that its surface normals form angles that do not exceed 10 degrees with incident rays that pass through the stop at all field angles; and
an infrared-blocking coating is provided on said at least one surface.
2. A single-focus lens for an electronic still camera which satisfies the following Conditions (1) and (2):
+66 +74 a +21 +0 6+20
. . . Condition (1)
+66 +74 b +21 +0 7+20
. . . Condition (2)
where
Δθa is the maximum deviation angle, throughout all field angles, between the principal ray of a light flux that is incident onto the lens surface having the infrared-blocking coating thereon and which passes through the stop and a line normal to the same lens surface at the same point of incidence as the principal ray; and
Δθb is the maximum deviation angle between a marginal ray in the central light flux that passes through the stop and is incident onto the lens surface having an infrared-blocking coating thereon and a line that is normal to the same lens surface at the same point of incidence as the marginal ray.