Abstract: An accessory includes an apparatus-side portion and an accessory-side portion to be attached to the apparatus-side portion. The accessory-side portion includes a surface, an internally threaded portion open on the surface, and an externally threaded member to be rotatably engaged with the internally threaded portion. The externally threaded member is positioned either in a retraction position by rotation of the externally threaded member in one direction or in an extension position by rotation of the externally threaded member in an opposite direction.

Abstract: A projection type display device includes a distortion corrector for correcting a projected image for distortions when the image is projected with a projection optical axis tilted with respect to a screen. The distortion corrector comprises a tilt angle generator for finding a tilt angle of the projection optical axis, and a display image corrector for correcting the display image using the tilt angle. The display image corrector comprises a two-dimensional table for storing corrected coordinates for four vertexes of the display image employing a vertical tilt angle and a horizontal tilt angle as variables, and a fixed point determiner for selecting one of the four vertexes as a fixed point.

Abstract: A zoom lens includes in order from the object side to the image side, a first lens unit of negative optical power and a second lens unit of positive optical power. Zooming is effected by varying the interval between the first lens unit and the second lens unit. The second lens unit has, in order from the object side to the image side, an aspherical positive lens and an aspherical negative lens.