Birth of "Click-Click" Maximum Aperture Indexing
This problem seemed intractable until Nippon Kogaku designers finally found the clue to a solution.
With all Nikkor lenses, aperture value is f / 5.6 with the meter coupling shoe in the 12-o'clock position.
Rotating the aperture ring clockwise to the limits opened the aperture to the maximum.
If a user always set maximum aperture with the lens aperture ring every time he changes the lens, the meter coupling mechanism might "memorize" the degree of lens aperture ring rotation at a point from f / 5.6 up to maximum aperture.
Nippon Kogaku designers introduced a double ring that sends lens aperture data to the exposure meter, by changing the resistance value of the variable resister in the exposure meter circuit, and coupled this special ring system with saw-toothed ratchet and shoe.
The shoe fell into the ratchet, and the shoe position sent information about degree of aperture ring rotation to the meter coupling mechanism.
This information was mechanically memorized in the meter system.
A photographer should reset the previously set value before performing maximum aperture indexing.
Nippon Kogaku designers intended to design the mechanism in such a way that rotating the lens aperture ring to minimum, then maximum setting released the shoe from the ratchet, set the maximum aperture of the newly attached lens and then the shoe-releasing mechanism would lock until the lens was detached.
A user could thereby perform maximum aperture indexing by rotating the lens aperture ring to one end, then back to the other end after mounting the lens.
In considering the optimal location for the lock mechanism,
Nippon Kogaku designers devoted themselves tirelessly to examining the action of the lens aperture ring and the body's meter coupling ring.
Two(2) facts about the aperture coupling shoe attracted their attention :
- it had a conical head.
- it was located near the camera body name plate.
The designers found that they might lock the shoe-releasing mechanism by rotating the aperture ring so that it rode over the conical head of the aperture coupling shoe, and that the reset mechanism fit behind the name plate.
Thus, semi-automatic maximum aperture indexing, called "Click-Click" operation, was developed for the Nikomat FTN.
The reset mechanism was stored inside the newly-thickened name plate (Photo 2.).
The reset mechanism was coupled to the exposed ratchet shoe of the aperture coupling ring (Photo 3., see arrow).
- Photo 2.
- Photo 3.
In the finished products, a shoe-releasing mechanism was locked by a projecting part on the back of the coupling ring pin, not the conical head of the aperture coupling shoe.
With the Photomic Finder of Nikon F and Nikon F2, which succeeded the Nikomat FTN, the conical head of the aperture coupling shoe was used to reset the previous aperture value for maximum aperture indexing.
Nippon Kogaku achieved something great, to the delight of photographers : sending lens maximum aperture information easily to the camera body without modifying conventional Nikkor lenses.
In 1977, after 10 years, however, Nippon Kogaku modified the Nikkor lens system and introduced AI (Automatic Maximum Aperture Indexing) Nikkor lenses.
Although I generally don't approve of considering "what if" in history, I sometimes try to imagine how different things would be if Nippon Kogaku had introduced an "AI system" earlier without developing the "Click-Click" operation.