Question on old lenses

[rodeo_joe1]

The notch for a big C Hook Spanner?

Not far off the truth I suspect.

I can vaguely dredge up memories of an early AF system that Nikon came up with before the 'screwdriver' attachment built into their lenses.

This prehistoric lash-up consisted of external AF sensors and a robotic lens twister that was matched to only two specially machined lenses when it first came out (one was an 85mm lens, and the other might have been a 200mm, I really can't remember that clearly). Anyhow, the contraption was heavy, bulky, expensive, and probably didn't work that well. So sales must have been dire.

 

Getting to the point. My guess is that the notch on early AF lenses was there to make them compatible with the above autofocussing robotic-arm contraption.

 

Also, you have to remember that consumer cameras are only part of what the erstwhile Nippon Kogaku group produce(d). I suspect that their industrial machine-vision department also had a use for lenses that could be externally robotically focused.