I intend to take up DSLR photography soon and am looking at either the Canon 40D or Sony 350. I own a Tamron 80-20mm conventional len with a 2x converter, with a Pentax mount, from the film era. Can this len be used with DSLR, if I were to change the mount to suit the camera? Any recommendation where to send the len and converter for cleansing? How much would it cost? Thanks.