Adding an ND filter to a fisheye lens is not always easy and in some cases it might not be possible at all. The good guys from cheesycam came up with a really cool solution which can cost you just a few dollars and produce apparently very decent results.
The Rokinon/Samyang 7.5mm 1:3.5 UMC Fish-eye lens (under $280 on Amazon) for micro four third cameras is a tiny little fish-eye lens with a pretty decent image quality in a very compact form factor. The only drawback – this lens doesn’t support filters (because of its front element). The cheesycam guys came up with an interesting low cost solution – adding a DIY drop filter in the back of the lens (this is a very common way of adding a filter to long range telephoto lenses but typically not to ultra wide angle ones).
All you need is a thin filter gel that you can connect to the back of the lens – the guys from cheesycam used inexpensive Rosco Cinegel 1.5 Inch X 3.25 Inch Swatchbook ($4.5 on Amazon). Now, they claim this will not interfere with the operation of the lens/camera in anyway – this might be true but you are putting something that does not belong inside your camera just in front of your sensor – so please do this at your own risk. Otherwise the demo looks cool and you get an ND filter with supposedly decent quality (at least for video) for under $5.
If you are unfamiliar with the use of ND filters – make sure you check out these videos on the subject here on LensVid.
You can also check out many more interesting DIY photography projects here on LensVid.