I'm interested in picking up a fisheye lens to do some really wide angle photography, but I want to be able to use ND filters to do some long-exposures as well. The problem is that m43 doesn't offer any super wide or fisheye lenses that will accept threaded circular filters (yes, I'm aware of the Olympus 9-18). I've seen the hack for the 7-14 Panasonic lens where you can make it accept gel filters at the rear, but that's kind of a hassle, and finding optical quality gel filters isn't as easy as buying circular ND filters (which I've already purchased). This got me to thinking, what if you took the lens cap from a Rokinon fisheye lens (do they even give you one? if not, can you purchase one? worst case just buy the one for the Panasonic fisheye), and cut the center out of it. Once the center was cut out, glue/epoxy a step-down ring in the hole of the lens cap, that way you could just screw whatever filter you wanted in to the threaded portion of the step-down ring, and slide the assembly over the built-in lens hood, enabling you to use whatever threaded circular filter you desire with a fisheye lens. Surely I can't be the first person to have thought of this, since it's a pretty simple hack. Has anyone seen something like this mentioned before, or better yet, have any results?