Options to consider:
Lee SW-150:, takes the 2mm filters, and can hold 2. Lee makes a Glass 150 x 150 CL-PL last time I checked, but their ND filters and grads are resin. The stoppers are glass, and Lee claims now that they have reworked the glass to help with the blue tint. Lee has a wide angle ring now that comes in 86mm, 95mm and 105mm and will let you use the SW-150 on any lens that will take one of those rings. The rings are heavy and on a 32mm Rodie, you really need to be careful as you are putting quite a bit of weight out past the copal, especially if you are using 2 filters.
There are 2 other brands to consider for filters for the Lee that I use, Nisi and HiTech. Both make a CL-PL and Glass ND filters. I have the Nisi CL-PL which is cool. (The Lee is warm). and I use Hitech 150 x 150 ND, 0.9 and 1.2, these are the Firecrest line and have built in IR blockage. Excellent glass but expensive and as they are glass, not resin, one drop and there it goes.
Standard round filters: You can sometimes find the Hitech firecrest filters in the 105mm size, and they are thin, with front threads. Again excellent glass. With the 35LS, you can screw them right on the threads of the lens, with no problems. Lee makes a CL-PL in the 105mm that is also thin and work well in this situation. The Lee CL-PL is warm, so you may have to adjust WB in post. This is what I carry when I carry my 35, 55mm and 75-150 as you can use step rings to adjust up to the 105mm size. I just prefer the screw in filters as they are both lighter and more secure in the field.
If you have the 28mm LS, you can purchase a Nisi filter adapter for it, or Lee, but I choose the Nisi due to cost. Nisi is heavier being all metal and will take 3 2mm filters. Just like the Lee it mounts to the front hood of the 28mm. This is the only solution I know of that will allow filtering on the 28mm, and still work without vignetting. You can use the sheet CL-PL and just rotate it for best polarization.
I have gone to the standard round filters on the 32mm Rodenstock, mainly due to the fact that they have so much less mass (not counting the Lee wide angle ring) so there is less weight on the front of the lens.
On the 40mm and up, you can go back to the Lee 100 x 100 system, and use the Wide angle hood, with 2 filter or 1 filter holders. I use the hood with 1 filter holder and then use the 105mm adapter on the front of the hood to mount a round CL-PL, either B+W or Lee.
If you want to slow your shutter speed down for 1 sec or longer in daylight, you pretty much have to use a filter of some sort and this in combination with a CL-PL to cut glare off rocks in the water, is main area I use filters. However at times it's nice to use a CL-PL to help cut sun glare off trees.
The Hitech filters are excellent but Hitech just does not make them very often, I waited over 1 year to get a 1.2 and 0.9 from 2filter.com. You can easily find the 150 x 150 and 100 x 100 sheet firecrest filters as B&H will have them in stock most of the time.
Third option is the Cokin X-Pro, but they are 130 instead of 150, so none of the Lee or Nisi or Firecrest filters will work, so I stayed with Lee for the 150 x 150 size.
Short video I made showing some of these filters and wide angle rings:
Paul C
