Adaptall 2 PKA mount question

What will this mount give me that a normal PK mount doesn't, and why is it worth £70?

As I understand it the PKA adapter will make the lens aperture known to the camera. This will allow AV mode on apertures other than wide open, is that right? Is that all it does?

Thanks, sorry if it's a silly question.

Having the "A" on the aperture ring of a lens enables all the exposure modes. It allows the lens and camera to communicate.

It would still need to be the right sort of lens in the case of the Tamron Adaptall, or at least I presume that these is a difference betweeen an Adaptall and an Adaptall 2 lens, apart from the mount.

Basically you can compare it to a Pentax K mount and a Pentax A mount (Auto aperture and metering). For the Adaptall PK/A mount to work correctly the lens has to have the AE setting on the aperture ring.

Thanks for the reply. Unfortunately i still don't really 'get' it I'm specifically asking about Adaptall 2 PKA mounts. The lens itself may or may not have an 'A' setting. Do you mean that a PKA mount won't accomplish anything when connected to a lens with no A setting?

Will a PKA mount let me use shutter priority mode with an Adaptall 2 lens? I guess I don't understand how the presence of a PKA mount will enable the camera to control the aperture. Thanks!

Crossed posts That was helpful, thanks.

So Adaptall 2 lenses with a AE setting on the ring hav some sort of mechanism which allows the aperture to be controlled by the camera (via a PKA adapter)?

Yes, the mount has electrical contacts that allow it to communicate with the camera body in the same way an A mount lens does.

Thanks guys