Hi Phil, thanks for tackling that monster question!
An easier way is to buy 1 good circular polariser that's as big as your largest filter thread. Then you can buy step up rings to make your 1 good polariser fit all you lenses.
So if I buy the large screw-in CPL filter and a number of adapter rings (allowing me to use the CPL filter on multiple lenses), will I still be able to fit a square Cokin or Lee holder? Will I be able to rotate the CPL filter independently of the square system?
it's possible to use the lens hood (difficult to adjust though) if you're using for example a 77mm C-Pl on a 77mm thread lens. If you're using a step up ring the the hood may well not fit.
Would I be correct in assuming that the step-up ring, the CPL filter, the Cokin or Lee adapter and the filter holder would pretty well act as a hood anyway?
you can buy bellows where filters drop into the 'hood'
What are bellows?
To selectively darken a sky you have two options - digitally or optically. Why not try digitally to start
I'll have to give it a go in the interests of learning, but I'm of the attitude that I want to do as much as I possibly can out in the open with optical equipment rather than spending more time that I already do in front of a monitor! haha.
several different densities - 1 stop, 2 stop, 3 stop
I take it the effect is the same as applied in the HDR technique? You're basically using a filter to physically apply 1 (or 2, or 3) stop's darkening effect?
Regarding B+W, it's not something I do often so won't be spending much time either taking or processing, but it's good to know about that software, cheers.
I've had a look through Cokin's website and youtube videos since I last posted, so I've got a better idea of how the assembly fits together.