Noob FL lens question

[steve_taylor18]

<p>Hi all, First post. I got my first ever fl lens today, a pristine FL 50mm 1:1.8. It's a mark 11, judged from the weight of it at 280g.<br>

Can anyone tell me what the little chrome stud is for that sticks out just above the locking mount mechanism to the left of the A and M marks. I have tride to push it in or pull it in every configuration I can think of in an effort to establish its purpose.<br>

An explanation would be most welcome</p>

<p>Thanks</p>

<p>Steve.</p>

[Bettendorf]

<p>It's a handle for your thumbnail to move the ring back and forth between A and M.</p>

[bob_miller4]

<p>The A-M ring makes the lens easy to use with manual aperture (M) when there is non-FL, non-FD hardware between the lens and camera body. <br>

This lens also has enough flare protection for the recessed front element, so it doesn't really need a lens hood when no filter is mounted.</p>

[cadillacmike]

<p>You would use it on M with say an older CanonFlex body, which had an incompatible auto-aperture linkage.<br>

Otherwise keep it on A - which is NOT the same as the A (or o) mark on FD lenses.</p>