Smudger
Member
My Pentax Spotmatic F also calls for a mercury cell, but since the meter is a bridge circuit it is "happy" with a silver oxide cell. Given that both my Spotmatic F and the SP 500 rely on the centering of the needle for setting the exposure I'm pretty certain that the SP 500 also uses a bridge circuit. Thus a silver oxide cell which will physically fit should be fine. BTW, check with Pentaxforums.com for good info on all Pentax gear.