The basic idea and rough sketch of the camera were presented on 2 June 1958.

In those days, Japanese camera manufacturers were copying foreign cameras. The design team was very much aware of the situation. They were searching for a new idea from a fresh perspective.

As snapshots became popular, photography enthusiasts dreamed of a camera that could be carried around anytime, anywhere and ready for shooting instantly. Viewed in this light, the design team reviewed the design of different types of camera and decided to develop a half-frame, fixed lens camera. They also examined the Konilette type camera. Because it required special purpose film and was not ever ready, this suggestion was abandoned.

28mm lens is the standard lens in half-frame format. The D. Zuiko 40mm lens was redesigned into a 28mm lens. The front focus (the distance from the front of the lens to film) of the lens is 29.5mm. They thought it was possible to make a pocketable camera of 32mm thick.

On the other hand, the design team doubted the quality of 35mm half-frame. They thought the advancement in film technology could compensate it. A 10"x12" print was enlarged from half of a fine grain processed 35mm negative taken by D. Zuiko 40mm lens. The photograph was showed to co-workers. They were asked what kind of camera was used. "Twin lens reflex camera?" they replied. According to this experiment, they convinced that half-frame format was practical if the film was properly exposed and processed.

After the research and experimentation, the proposal for the new camera was handwritten into an A4 paper:

The proposal was materialized with the agreement of the General Sales Manager. In fact the idea of the camera was from a young designer, he was also responsible for the design of a series of other Pen models.

Film advance is by means of winding wheel at the rear of the camera. This can be done easily by the right thumb. The film advance wheel is settled on the film advance sprocket. It employs the minimum number of gears. This greatly reduces the production cost.

All Pen series lens-shutter cameras and Trip 35 camera use this film winding wheel. Over 20 million of them were produced, the cost saving amounted to several billions Yen.

The engineer of the camera himself designed the exterior of the camera. His design was superior to that of an outside industrial designer. This deserves special mention. The height and depth of the final camera is larger than planned. But it is good enough.

Many people claimed that the name Pen was their idea. A full-time patent lawyer of Olympus suggested, "How about Pen rather than Memo?" This is a true story.

Early production of Pen was at a loss. Production department said, "This loss won’t do any good!" But the Pen series became the breadwinner of Olympus after progression in manufacturing technique and increased production.

Because of its high lens quality and portability, Pen was regularly used by professional photographers as their secondary camera. The excellence of Pen cameras was proved in the "Pen Meisaku Snapshots Exhibition". (Meisaku is a Japanese homophone joke. Like hour and our. Originally, Meisaku means masterpiece. But here, Meisaku means not masterpiece but interesting.)

The Pen laid the foundation of half-frame format and created the great half-frame camera boom in Japan.