I have a question for any owners of the PL 42.5: Have any of you used a 67-58mm step down ring on your lens, with no vignetting wide open? I'm thinking of possibly picking up a Nocticron, but I'd like to be able to use all of the 58mm filters I have with it (two CPL's, a 3 stop ND, a 10 stop ND, two variable ND's). I'd be curious to know if a 58mm step down ring can be used without causing vignetting. If no one has tried this, could you measure the diameter of the front element? I'm curious to see just how much land there is between the edge of the front element, and the filter ring. From the best I can tell, it appears that there is at least 5mm of space between the edge of the element and the filter threads, so it should be able to accept a 58mm step down ring, but I'd like to have somebody actually measure the element to confirm my thoughts. Thank you in advance for your help!