The Pen EE
is a half frame camera, meaning that for a roll of film, where you would usually get 36 exposures, the half frame gives you 72 exposures.
It was introduced in 1961 and was the amateur model, with fully automatic exposure and fixed focusing. It is a true point and shoot camera, and has a 28mm f/3.5 lens. The Pen EE family is easily recognized by the selenium meter window around the lens.
The Pen EE.S launched in 1962, is the same model with a 30mm f/2.8 and a focusing ring, made necessary by the wider aperture.
In 1966 the two cameras were slightly modified and became the Pen EE (EL) and Pen EE.S (EL) with a modification of the take-up spool to make film loading easier. EL stands for Easy Loading. You can only recognize them by a small label marked EL stuck on the front, or you can open them and look at the take-up spool.