Maitani had been keeping a serious attitude to his work after the accomplishment of the Pen camera. He pursued two concepts in the development of the Pen series. One was the sophisticated secondary camera for Leica camera users. And the other was the simple camera for general people.

Maitani :
"On the development of easy-to-use camera for women or those whom are not familiar with machinery, I adopted the half-frame format to reduce focusing error. However, complicated exposure technique was still an obstacle to the popularization of camera. Then we started the research of the EE (Electric Eye - automatic exposure) system."

Because of its simplicity, the Sales Department strongly opposed the Pen EE. However, the executives changed their attitude quite abruptly after they saw the prototype.

"Way to go! This can be priced at 10,000 Yen!" The Sales Department added 2,000Yen to the Maitani's estimation of 8,000Yen.

A year later, Pen EES with two shutter speeds of 1/30 and 1/250sec was released. The shutter was produced by Olympus. Pen EES is the world's first programmed automatic exposure camera.

This automation was successful and made an unprecedented hit in the market. Olympus couldn't meet the huge demand. The Sales Department inquired to the factory everyday about the production schedule to stock just one more camera for the enormous back orders.

The Pen series total production amount reached about 17,000,000 units in 20 years. And more than half of them, about 9,000,000 units, were Pen EE and Pen EES. It was an enormously large sales. Camera was popularized all at once, it pervaded among women just as Maitani wanted.

The Olympus Pen name was featured in a commercial song on radio and TV. It was a common scene to hear children chanting the melody "Pen, Pen, Pen, Pen" to themselves while playing.

Ihee Kimura, one of the great Japanese photographers tells an occasion with the Pen camera. "I witnessed a woman was taking a picture of her baby in her arm at a terrace house." ( from the discussion "The way of Japanese camera after the 2nd World War", Nihon Camera magazine.)

Maitani:
"At that time, not only low-priced cameras but also SLR cameras became popular. I was thinking about the detailed design of a half-frame SLR during the development of the EES. When a boss told me "How do you think about half-frame SLR?", I readily took out and showed the mechanical layout design sheet from my desk. Then the boss replied "Excellent! Go for this!" I got the green light instantly."

The rotary metal focal plane shutter is also a new invention.

At the beginning, the top shutter speed achieved was an unthinkable 1/60sec. The way to increase the speed was to the reduce the weight of the disk. Usually thin steel sheet was used for apertures and shutters, it was too heavy to rotate faster.

So the development team tried aluminum. When the shutter was stopped, the sudden force caused a massive shock and the aluminum sheet crumpled like a sheet of paper.

Next material tried was titanium. The shutter speed was able to increase to 1/300sec. But it still wasn't fast enough. If the the titanium was thinner, it was not strong enough.

To make the disk even lighter but with the same strength, a technology used in microscope manufacturing was applied. The titanium was etched in the center leaving it thick at the circumference.

The speed of 1/500sec was achieved when the spring was strengthened. But the spring would break after a few repetitions due to metal fatigue.

Finally the problem was solved by using a special spring made of Swedish steel.

Unlike conventional focal plane shutter, it opens completely at one time, this allows flash synchronization up to the highest speed of 1/500sec. And the rotary shutter always rotates in one direction therefore the interlocking device is very simple. Only one pin is needed to control many devices. This is similar to the Pen EE's self-cocking device.

Maitani acquired about 50 patents by the PEN-F.

Maitani:
"Conventional focal plane shutter with its shutter curtain is too bulky to be used in the half-frame SLR. I invented the metal rotary focal plane shutter to make use of the space behind the prism."

"Excellent!" This is what the three Leitz engineers said after they examined the Pen- F for about two hours during the 1963 Photokina.

At that time, Japanese camera makers were stealing the design and technology of German cameras. In this controversial situation, Japanese new products were always scrutinized. But the originality of the Pen- F design was admired by the Leitz engineers.

Maitani:
"Absolutely! Japanese makers were always copying German cameras until then. No wonder they wanted their original ideas to be respected and protected. But I invented the completely new mechanism. That is why they said "Excellent!"."

Eiichi Sakurai:
"It would be nonsense to create a half-frame SLR just for the satisfaction of making it a little smaller. This gave the design team some headaches, but at the same time it was as much their own philosophy as it was the company's."

Camera industry was in the forefront when Maitani was developing the Pen series. It is similar to computer software industry of today. New products always had high news value.

Maitani:
"I was lucky that I could be a designer of a prospering and my favourite industry. I motivated myself to create the camera that I wanted. I designed it by myself because I couldn't be satisfied with any other cameras. Some people say originality is the characteristic of the cameras I designed. But for me, they are ordinary cameras."