Abstract: A compact zoom lens is constructed with, from front to rear, first, second and third lens units of positive, negative and positive refractive powers, respectively. A diaphragm is positioned in or adjacent the second lens unit. The second lens unit and the diaphragm are stationary. When zooming from the wide angle end to the telephoto end, the first and third lens units are axially moved in such a manner that each of the separations between the first and second lens units and between the second and third lens units is increased monotonically.

Abstract: A conversion lens upon attachment on the image side of a master lens increases the focal length of the entire system. The conversion lens comprises three components of negative, positive and negative powers in this order from the front, has a negative power as a whole, and satisfies the following conditions:2.0<f1/f3<4.00.8<.vertline.f2/f3.vertline.<1.2n1-n2>0.15where fi and ni are the focal length and the refractive index of the glass of the i-th component counting from the front respectively.

Abstract: An Albada finder is constructed of an objective lens, a reflection layer, a field-of-view defining frame, and an eyepiece arranged in sequence to provide a mirror image of the frame from the reflection layer to the eyepiece. An optical device of positive power is arranged outside an optical path of the finder. An information source with an information display plate and an illuminator for illuminating the display plate are arranged so that light from the display plate comes through the optical device into the eyepiece as an oblique beam. This shortens the distance from the reflection layer to the eyepiece while achieving a sharp information display.