My recent video with a fisheye lens has brought up the question about how to block incoming light on a bright day. On a typical lens you would screw an ND Filter to the front. Due to the design of many fisheye and wide angle lenses, they are unable to accept threaded filters.
On a bright day, you end up stopping down your aperture as much as possible, and sometimes that's still not enough. Simply holding a glass ND filter over the front of your lens can help, but you'll be prone to internal reflections bouncing off the fisheye back to your filter.
So if you run into this problem, here's a simple and yet very effective way to add an ND filter to your fisheye or super wide angle lens using inexpensive gels.
If you want to maintain sharpness, get a decent filter. The Rosco gels are great quality, inexpensive, and as you can see there's not too much loss in sharpness in my tests. Keep in mind i'm using a flat Cine profile on the GH4 with no sharpening added in post. You can punch this image up even more if you think you have the need.
For such a small piece I suggest grabbing the Cinegel Creative Kit (found here) which includes a bunch of different ND filters and creative colored gels.
Rosco Cinegel Swatch Creative Kit
If you need a larger piece, those too can be purchased in larger individual sheets (found here)
Rosco Cinegel ND Filter Sheets