Learning more good stuff about Canon FD lenses on the NEX-7

Started Jul 10, 2013 | Discussions thread
wb2trf Senior Member • Posts: 2,914
Riquez is the first to get this right. A few more points.

His first key observation is that A=P when a manual lens is attached.  When an automatic lens is attached the meaning of choosing A is that you assert control of aperture, taking that control away from the camera.  That assertion of aperture control with an automatic lens is all that A means.  When you attach a manual lens with an aperture control ring, A becomes meaninglessly equal to P because the camera can't control aperture anyway, only you can.  An assertion of control by setting to A is meaningless since the camera is powerless to control aperture anyway.

With a manual lens the most meaningful remaining settings are the choice between P and S.  Obviously with P you only control the aperture and focus, everything else is up to the camera, or can be if you also choose AutoISO.  In P you can use EV+- and the camera will trade off between shutter speed and ISO.  With S you assert control of shutter, you already have control of aperture via the ring, so the camera can only control ISO if you choose auto ISO.  EV+- still works, as a different way of setting ISO that gives you access to finer gradations of ISO control.

Unlike with a manual lens, with an automatic lens M has a important meaning.  It means you are asserting direct control over both aperture and shutter.  There is no other way to do this, other than M, with an automatic lens.  However, with a manual lens M is somewhat meaningless and slightly restrictive compared to S.  Its only effect, compared to S, I believe, is to prevent you from choosing AutoISO and to turn off access to EV control both of which are, in effect controls on you rather than on the camera.  Therefore with M you give up the ability to select intermediate ISO settings via the EV control while gaining no more control over ISO, which is still directly settable in S, if you want. Therefore I think M is a negative value with a manual lens.

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