With extreme wide angles lenses, let's say 20mm and under, have you have to use step up rings when using filters and then adding hoods. In my own case, a recent 19mm Vivitar purchase causes me to think that I may have to go from a 62mm thread up to a 67 or even 77mm thread once I put a rubber hood on. What's your experiences.
I stumbled across a website once that had a calculator that helped you design a lenshood to match your lens. Sorry I can't remember how to find it, but maybe somebody here will.
For filters, first I try not to use and when I use filters on really wide lenses, I use gels. Lower distortion. Some folks put filters inside the camera.
It probably depends on the lens design. I only have rubber hoods on my Pentax 645 lenses. The 35mm Pentax lens is roughly the equivalent of a 21mm and takes a 77mm filter. I use a 77mm rubber B+W wide angle lens hood with this lens and standard Tiffen and B+W filters with no vignetting. I also use this same hood on my 45mm Pentax lens with a step-up ring and 77mm fiters.
Be sure the lens hood is for wide angle lenses. The B+W wide hoods are really dish-shaped.