I must not understand how the FL works.No. You compose and focus the same as you would with an FD lens. You meter with the camera set in its stop-down mode. You do not have to have the lens set in stop down mode when you trip the shutter -- you can if you want, but the camera will set the aperture anyway to its pre-determined value when the shutter is tripped. It is very important that, if you use the camera's onboard meter, you meter with the stop-down lever engaged and then you set the meter needle to the stop-down metering index mark. With respect to the needle, I'm thinking of the AE-1, FTb and F-1. Those cameras with digital or LED readouts will handle the index differently, but the concept is the same.
I am reminded of the Canon A-1 as an example. That camera has a "Stopped Down AE" mode, which is essentially Aperture-Priority AE with the lens set to manual aperture mode. It stays stopped down when the shutter is tripped. But with other cameras, such as the FTb, EF, or original F-1, you can stop the lens down momentarily to meter -- or you can set the stop-down lever to stay put for manual aperture during exposure. Either way works.
How can an FL lens stop itself down when the shutter is clicked...isn't that why it is not an FD.?
If i do not have the Stop Down button pushed, won't an FL Lens be wide open when the shutter is clicked.?