I have a Minolta AF 35-105, 3.5-4.5 (the older beer can one) with adapter. When I put it on my G2 I can't figure out how to change the aperture. The only rings on the lens are focus and zoom. Nothing I do on the camera itself seem to change it or indicate what it is set at. As you can tell, I am somewhat new to this. Any help would be appreciated.