Great forum, I'm hoping I can contribute a little as I do almost all of my filming outside on location filming wildlife etc in some pretty tough conditions. I usually end up making my own gear dollys and jibs etc. The last item I made was a waterproof housing for my POV HD camera. Anyway I was wondering if anyone could shed some light on this question. A lot of my stuff is done by water so I purchased a star filter from Format 4x4, I have noticed in bright light conditions on water I get a Kaleidoscope effect and not clear stars. Is this expected behaviour?
Stars are effected by the f-stop and the size of the source. Point sources with lots of contrast give better stars, and smaller f-stops give a sharper more defined star. Example, shooting into lights will produce stars, but shooting a bright concrete wall lit by the same lights, will not. A large glare type reflection from the surface of the water will not give a star. For that you need a glint from a ripple.
You might try to combine the star filter with a Polarizer to cut down on overall glare.
Or you can add them in post pretty easy.