Abstract: Fluorescent screens and display systems and devices based on such screens using at least one excitation optical beam to excite one or more fluorescent materials on a screen which emit light to form images. The fluorescent materials may include phosphor materials and non-phosphor materials such as quantum dots.

Abstract: A lens system according to an aspect of the present invention includes a focus operation member for manual operation of a focus of a taking lens, a focusing direction detecting device which detects a moving direction of the focus for setting a focused state with respect to a present position of the focus, as a focusing direction, an operating direction display device which displays an operating direction of the focus operation member for moving the focus to the focusing direction on the basis of the focusing direction detected by the focusing direction detecting device, and a reversing device which reverses the operating direction displayed by the operating direction display device.