I can't compare the two since like you, I researched both and only bought one...the Pentax. I do use a step-down ring with the adaptor but only a 55-58mm for the Tamron 90/2.8 and sometimes a Phoenix 100/3.5. Since my needs were for Macro rather than traditional ring light shooting, I chose the Pentax partly on name but more because its lighting elements curve around the diffuser more than just point sources of light, and provides reasonable left-right brightness control. If I used the Pentax macro lens the Pentax ring light includes some super-duper adaptor that is no use to me at this time. It comes in a nice boxs with foam cutouts for all the parts. So far I am pleased with it and the cord is not really a problem as I just let it curl around the lens to keep it out of the way.
But all my experiences aside, if I needed to shoot with a 72mm or 77mm lens I would want to worry about the 77mm above all else since thats a lot bigger than the Pentax light. My only 77mm is the da*300 and looking for vignetting with that would not help you much. My guess is that the Pentax would work fine with your 72mm 180 lens, however here's to hoping someone with that combo replies. Good luck.
|