Complicated business this filter stuff!
Yes, I can see how mounting the Lee filter on top of a screw-on polarizer will complicate things and is best avoided. I have some thoughts and further questions:
Lee wide/normal adapter rings
Lee is a little light on details until you start digging, but I finally found some info here:
Will a Wide Angle Adpaptor Ring work on any lens?
A Wide Angle Adaptor Ring will have no detrimental effects if used on standard or telephoto lenses.
Seems a little odd why Lee would make a "normal" ring as well when the "wide" one works with any lens and even costs the same (according to my findings at B&H photo). Oh well, I'll go for the "wide" ring then as I prefer to add my own vignetting
Square or screw-in polarizing filters?
I can see situations where I'd need all 3 filters in use at once (e.g. a seashore scene in the sunset with "misty" water and less reflections in the water/wet rocks), but there are other situations (traveling etc.) where I'd want to have a less bulky/fragile and less conspicuous polarizer. A screw-in polarizer (B+H, Zeiss, Heliopan or whatever) would fit that bill nicely I suppose. If I only could also use one of those with the Lee filter holder all would be well.
Lee round shaped polarizer directly on lenses, or not?
I think I've figured it out... Lee has a 95mm round shaped polarizer which I assumed could be used both with the filter holder (using Lee's "Accessory ring") and attached directly to a lens (using step-down rings for lens diameters less than 95mm), but apparently not so.
According to my findings the advantage of its round shape is that it doesn't demand the "Lee Professional kit" filter holder (allowing independant rotating of the filter slots, which I believe is needed if you simultaneously want to use 100mm square shaped ND grad filters), but instead allows for rotating the polarizer within the normal lens holder.
Not very helpful for me
So, can a regular screw-in polarizing filter (82mm or larger obviously since my widest threaded lens is 82mm) be attached to the Lee filter holder? This is what I found when digging a little further into Lee's site:
Can I use my existing screw in polariser with the LEE Filter Holder?
Providing your polariser has a repeat thread to accept the LEE adaptor rings the there is no reason why you cannot use existing screw-in polarisers with the LEE System. Bear in mind however that polyester filters, if used in the holder in front of polarisers, will stop the polariser working correctly. Also vignetting problems may occur on wide lenses in the system is not as close to the lens as absolutely possible.
So what is a "repeat thread" and how exactly do you attach a B+W/Zeiss etc. round shaped polarizer to the filter holder?
Also, would I need to buy a 95mm polarizer to avoid vignetting with either my 24-70 lens (82mm thread) or if I buy a 17-40 (77mm thread but a wide-angle lens) and use 95-82/95-77 step-down rings when attached directly on to the lens without any additional filters?
I had my eyes set on the "DSLR starter kit" which seems like a great deal, but upon further inspection I believe it only takes two filters (I'd want one which takes an ND, a grad-ND and a polarizer. I also hear the filter-pouch is quite useless (hard fabric which might cause scratches and doesn't do much for protection), so that might just be a waste of money.
The "Foundation kit" on the other hand takes 3 or 4 filters (Lee can't seem to decide as they have conflicting info on the same page -can someone confirm how many it'll take?), so this is probably a better route to go and buy the 0.6 ND Pro glass and 0.6 ND hard grad resin filters on their own?
Obviously a normal hood won't fit with the filter holder in place (nor with a large (95mm?) polarizer with step-down rings for my various lenses, so will the Lee hoods solve this problem? And will they actually cover the lens all the way? The illustrations at Lee's site seems to show a "universal" hood with an attachement that slides into the holder (I assume the frontmost free slot) meaning that it'll leave the area behind it in the open. Not ideal. The wide angled hood seems to work in the same way. I'd like to hear from someone who uses them, or has other solutions for a hood.
Safe storage/transportation of filters
How do you best store and protect those 100mm filters? Another thread here addresses the very same question where a couple of people reply that the Lee 10 filter pouch is the one to go for. Is its material/build different from the 3 filter pouch? Are there other ways to protect filters like these? Hard plastic containers which take a beating perhaps?
My first use for filters is to shoot mountains. I believe both grad ND and polarizing filters simultaneously will be needed for that. And for waterfalls I assume I need to exchange the grad ND with a full ND filter and keep the polarizer on. In any case I need to find a solution where I can use a polarizer with one or both of the ND filters.