The Pen series is a family of half-frame cameras made by Olympus from 1959 to the beginning of the 1980s. Aside from the Pen F series of half-frame SLRs, they are fixed-lens rangefinder cameras.
In 2009, Olympus introduced the PEN E-P1, a Micro Four Thirds system digital camera which the company touts as the next-generation Pen camera. All Olympus PEN digital camera series have built-in sensor-shift image stabilisation and (except for the E-P1) can use optional electronic viewfinder which should be slid into its hotshoe.
The original Pen was introduced in 1959. It was designed by Yoshihisa Maitani, and was the first half-frame camera produced in Japan. It was one of the smallest cameras to use 35mm film in regular 135 cassettes. It was thought to be as portable as a pen; thus the name. The idea was to be much copied by other Japanese makers.
A series of derivatives followed, some easier to use with the introduction of exposure automation, e.g. the Pen EE; others with a wider aperture lens and a manual meter, such as the Pen D.