Lee Foundation Kit is available at B&H

[Richard Lane]

Rich, Lee does have a square one, but to use it you have to rotate your holder This would make it hard to stack additional filters on top. To me this kind of defeats the purpose of having the filter holder in the first place. Or is there a different set up that I don't know about?

Rick

Rick,

Yes, Lee makes a square Circular Polarizer (CPL), square linear polarizer and round CPL. (For people that aren't sure what to get, you always want a Circular Polarizer (CPL) whether it's square or round if you would like to maintain AF, because linear polarizers confuse the Auto-focus system of the camera).

You don't have to rotate the entire holder to adjust the square CPL, you can just pull it out of the holder and rotate the square CPL filter in 90 degree increments until you get your desired affect, and then put it back in the holder. You do loose some fine tuning with the square CPL, however you probably don't want the full CPL effect with wide landscapes including the sky, and the full CPL affect also reduces the look of flowing water. If you need fine tuning of the square CPL, then of course you can turn the filter holder and if you have a solid ND in another slot, then it won't affect that either, however you would have to handhold the GND or add extra slots and risk vignetting again. The circular CPL can be fine tuned by turning the dial in less than 90 degree increments.

The square CPL has the advantage of being cheaper, thinner, and being mounted closer to the lens there is less chance of vignetting. You also save money on not having to buy the accessory mounting ring. The disadvantage is that it takes up a slot on the filter holder, which can limit you from adding an additional solid ND and/or GND to the holder or you can always add extra slots and risk vignetting once again.

I'm definitely not pushing the square CPL, I happen to have both the Lee 105mm CPL with accessory ring and the square CPL. I prefer the 105mm round CPL with ring adapter. The only reason I bought the square CPL was because they are always out it and I wanted to own it, because I've heard that the 105mm can vignette with ultra-wides on FF, which is the direction I'm headed in.

Rich