Nikon’s Roots Vol.13 – Nikon Photomic FTn

The second installment of the gacha system

The “gacha-gacha” system developed for the previous Nikkormat FTn was welcomed by users. Although a certain ritual of rotating the aperture ring back and forth between the minimum aperture and maximum aperture is required when mounting an interchangeable lens, the troublesome task of reading the maximum aperture of the lens and realigning it to the film speed scale each time is eliminated. Additionally, the Nikon F-mount lenses that were in stock could be used with the latest TTL metering devices as they were, making this system a lifesaver for both users and manufacturers.

So next up, it was time to incorporate this system into the flagship Nikon F. This led to the Nikon Photomic FTn, which appeared in 1968. The Photomic finder alone was changed to the “Photomic Tn” which had a center-weighted metering mechanism incorporated into it, the “Photomic FTn” finder, but perhaps because the name of the camera it was attached to was thought to be a bit unsound, “Nikon F Photomic FTn,” the “F” was omitted and it became “Nikon Photomic FTn.”

Aperture linkage mechanism

In developing the Nikon Photomic FTn, Nikon completely reconsidered the aperture interlocking mechanism. In the case of the Photomic, the pin that transmits the movement of the claw moves along an arc. Previous Photomics had a mechanism that moved the interlocking pin along a rail that was provided on the nameplate to guide the interlocking pin on the Photomic side, but the Photomic FTn replaced this with a four-bar link, commonly known as a pantograph. A four-bar link is a mechanism in which four arms are connected rotatably by pins on both ends, and is also known as the mechanism used in train pantographs and drafting equipment. In cameras, the equivalent would be the mechanism that moves the thin plate that makes up the curtain of a square focal plane shutter in parallel with two arms.

By using this four-bar link, we were able to significantly reduce the space required for the interlocking mechanism, which also contributed to the overall miniaturization of the Photomic. This can be seen from the smaller area of ​​the nameplate when viewed from the front.

The benefits of miniaturization

This miniaturization brought about several benefits. When attaching or detaching an interchangeable viewfinder such as the Photomic to a Nikon F body, the tabs that pop out from the left and right sides of the viewfinder screen are retracted by pressing a button on the back. In other words, these tabs secure the viewfinder to the body, but when the viewfinder becomes larger like the Photomic, the strength of the tabs becomes weak. So, with the Photomic FTn, a fixing lever was added, taking advantage of the space that was freed up by changing the aperture linkage mechanism. The tab that operates this lever firmly holds the nameplate on the body from both sides and fixes it. This was originally a fixing method used with the external linked exposure meter Nikon Meter, and although the operation is a bit more complicated, it provides a more reliable fixation. The previous fixing method using the tabs on the left and right was still retained.

In addition, the nameplate was moved back, so the aperture display on the aperture ring, which had been hidden until then, became visible. As a result, the aperture display window that had been located above the eyepiece on the back of the viewfinder up until the Photomic Tn was eliminated. However, it is thought that this was also due to the fact that it became impossible to retrieve absolute aperture information from this position due to the rattle mechanism.

One other interesting change…

Also, although it is not an advantage of the smaller size, the white battery check button that was on the Photomic Tn has been removed, and instead, you can now check the battery by pressing the button on the top when the camera is turned off. This power switch has been used since the middle of the first-generation Photomic; pressing the small button next to the viewfinder causes a button on the top just above to pop out and turn the camera on. Pressing this button turns the camera off, but pressing the button on the top again gives the camera a battery check function. The battery case, which holds two HD (MR9) type mercury batteries, has also been changed from the previous type that was accessed from the side to a type that can be accessed from below by removing the viewfinder.

A gacha mechanism

Unlike the Nikomat FTn, the exposure meter interlocking mechanism is quite complicated because the direction of the rotation axis of the aperture ring and shutter dial is different. As with previous Photomics, the movement of the aperture ring and shutter dial is drawn around the roof of the pentaprism, and information is input to the light metering circuit via a variable resistor, but in the Photomic FTn, the ratchet teeth and pawls work together at the fan-shaped gear that receives the movement of the four-bar link to read and set the maximum aperture. It seems that they judged this to be more advantageous in terms of friction than the variable resistor with a larger diameter.

The Photomic FTn also takes advantage of the four-bar link mechanism in terms of the mechanism for resetting the set maximum aperture. When a lens is attached, the Photomic interlocking pin works with the claw, pushing the pin up against the side of the claw and then dropping into the valley of the claw. This upward movement is picked up by the link lever, which releases the ratchet claw. Resetting is possible without adding the mechanism behind the Nikomat FTn nameplate.

The inherited linkage mechanism

With the Photomic FTn, Nikon’s Photomic series TTL metering system reached a state of near perfection. The ingenious mechanism using a four-bar link was later carried over to the Photomic of the Nikon F2, and continued until it was replaced by AI in 1977. This clattering system caused Nikon SLR users to get used to the ritual of changing lenses, and even with AI-type lenses that were no longer necessary in later years, there are still stories of users unconsciously turning the aperture ring back and forth from minimum aperture to maximum aperture when attaching the lens.