You would still get a focal length of 11-18mm BUT you will see vignette in the viewfinder as the lens will not be able to project an image circle to fully cover the FF sensor.

The output however will be automatically cropped to APS-C size thus the A900 will give the same output as any APS-C camera.

If the A850 can recognise the Tammy lens as an APS-C lens then you can use it. The image will be cropped automatically.

Wah jumping FF trus? congrats dude. No wonder A900 @ Alphantics go till 7k++

edit : i thought you jumped ship right?

Braynumb : Yea la. Cheat us all. Say need to pay debts and all. But mana tau Canon 40D. Zzzz.

the reason i like on sony compared to others is coz of its DRO and SSS. Apart from that, setting wise, its all user changeable and if all else fails, there's always PP in hand.