A variety of the front mounted type wide convertors have been hitherto proposed as conversion lenses for use in imaging devices such as still cameras and video camcorders, in which these convertors are configured to be mounted on the side of object to be photographed, or in front of imaging lens, and to change the focal length of the imaging device as a whole to the wide-angle range while maintaining the focal plane of entire imaging lens system at a fixed position.
For example, a wide-angle conversion lens is disclosed in Japanese Unexamined Patent Application Publication No. 2002-214529, to be mounted on the object side of a zoom lens as a major lens system and capable of expanding the image angle of the entire lens system. This wide-angle conversion lens is formed of three lenses, including a concave meniscus lens having a convex face thereof facing the object side, an aspheric lens of plastics, and a convex lens placed on the object side further from the concave meniscus lens.
In addition, among conversion lenses there may be mentioned a wide-end convertor formed only of one group of concave lenses (inclusive of single concave lens). By mounting this wide-end convertor formed of one group of concave lenses (or one concave lens), the focal length at only a wide-angle end is changed to the range of further wide-angle and the photographing becomes feasible at wider image angles.
The class of lens such as a wide-end convertor is suitably adapted to less expensive and light weight use, on the one hand, because of the relatively simple composition of the lens mounted in front of the zoom lens of imaging device body, but it can be focused only at its wide angle end. As a result, the wide end convertor itself may need to be dismounted from the imaging device body when the photography on the telephoto side is intended.
Furthermore, there also cited among conversion lenses is a close-up lens for enabling macro photography. For the close-up lens as well, the operation of mounting/dismounting may be required for switching between macro and standard photography.
In view of the above-mentioned and other difficulties, it is desirable to provide a conversion lens and conversion lens system for enabling the switching from the standard focal length range to either wide-angle or macro range, and vise versa. Further, it is desirable to provide an imaging device incorporating the conversion lens and conversion lens system.
USPTO Backgrounds
USPTO Backgrounds