Vivitar 400mm 15.6 "L" ?

Image of Vivitar 400mm 15.6 Komine Auto Tele S#28+ ... what does the "L" do?
As far as I can tell, nothing inside the camera activates this. It is movable, and can be pushed in or out.
So what is its proper position?
Thanks for any help.

Found the answer:
"Some FD lenses have a switch on the back to set the aperture for manual operation. If you see a switch on the back of your older lens and its set to "L" then move it away from the "L" to set it for automatic operation. (Here when I say "manual" or "automatic" I'm referring only to the operation of the aperture, not the automatic exposure capability of the AE-1.)"
AKA ~ https://www.photo.net/discuss/threads/canon-fd-lenses-not-performing-auto-exposure-on-ae-1.349403/

The text above is ambiguously worded.

The lever at those FD lenses is not to switch between manual and automatic aperture setting (that is done at aperture setting ring) but to lock the lever that stops down aperture. This enables stopped down operation without use of the stop-down (DOF) switch at the body. As when using non-coupled extention means or when flipping the lens.

Yes, I assume that L-mark indicating such locking function too. Though I got no idea how...

Most Canon FD-lenses have the automatic-diaphragm lever arrest when pushed manually to the end of its way. Only a few early lenses lack that self-arrest and need a manual lock.

Yes your correct, on this lens there is a green dot, that is for automatic aperture setting on the ring. But it was interesting to find out, that when this "N" switch is set to the right, as the arrow directs, a physical stop is put in place. One has to first push the metal tab counterclockwise, then activate "N".



(**This image shows the lens disassembled, having trouble putting it back together again, Sigh:
(there was a url link here which no longer exists)

That would be the same as with the older Canon lenses I hinted at.

You push that lever (automatic-diaphragm lever) to the end of its way, arrest it by means of that knob and then set the aperture of your choice at the aperture ring. (Or the other way round if you prefer.)

I assume the enigma has been solved

NO!! Dang gum it... looked at it several times today.. just updated that post.