I am looking for recommendations on ND filters, specifically a ND8, ND16 and ND32 filter.
I read that Tiffen makes excellent filters, so I looked on their website and only saw filters as dark as ND8, but I did find the Tiffen 77mm Variable Neutral Density filter, which goes from 2 stops to 8 stops down.
Are people generally using a specific ND32 filter, or are they using the variable one?
A variable ND will make it possible to do a smooth exposure adjustment similar to a video iris pull during a take (as opposed to the 1/3 stop increments in Canon EOS lenses). The variable ND will normally give you from 2 up to 8 stops of adjustment.
Choose a good brand though, cheaper versions do tend to affect resolution. Buy one to fit your largest lens front diameter and buy step up rings for your smaller lenses, then you will only need the one variable ND filter.
Regular ND filters are normally in .3 increments (1 stop) so should be available as .3, .6, .9, 1.2 etc. As well as Tiffen Schnieder also make good quality NDs.
If you have a matte box you can slide them in and stack for more ND cut rather than screw each filter on, but this is not as convenient as being able to rotate a variable ND for perfect exposure. You'll have to change the variable ND (normally a screw on filter) every time you change the lens though.
Casey - I paid $33 for an Opteka 77mm variable ND filter with step rings for smaller lenses. As Phil says, it is a lot easier to rotate a variable than to screw and unscrew individual filters. I have had no problems with resolution or chromatic aberration. Out of stock at 47th St Photo through Amazon, but you can get it from their eBay store.