I have a FD lens and a Nikon Non Ai lens, with two adapters respectively.
Attached the FD lens to EOS M, set to M mode or AV mode, the aperture is fixed 00. Press the shutter button, it doesn't fire.
How to use these vintage lens on EOS M?
by Paul Cezanne
In Custom function menu: C.Fn-7 Release shutter without lense: on
The shutter can release.
It can shoot in either mode, including P, AV, TV, M. In TV mode, set ISO to auto. ISO becomes a variable according to time and aperture you set.