Usefulness of a Broken Polarizing Filter

Question

I picked up my camera bag a few days ago, which was not zipped shut. Out fell two of my lenses. In the process I broke the focus motor on one lens and cracked a Hoya HD polarizing filter on the other lens. Looking at the damage to the polarizing filter I can see that only the front piece of glass (the part that spins) is cracked. The inner piece of glass is unharmed. I have three questions:

1. Is it possible to get just the outer piece of glass replaced by Hoya for a cheaper price than buying a brand new filter?
2. Assuming the answer to #1 is no, is the inner piece of glass useful for anything? Can is act as an extra protective filter? Does it still have some polarizing effects without the outer piece of glass attached.
3. If the answer to #2 is yes, does anyone have any suggestions on how to safely remove the outer piece of glass from the filter?

Answer 1

1. That's possible, but it doesn't sound likely, as that is the actual polarizing filter. Judging from filter prices, that is the most expensive part of the whole filter.

2. The back glass is a depolarizer. The only use for that (other than as a protective filter) would be if you put a linear polarizing filter in front of it, because then you get a circular polarizing filter.

3. If it's built the same as the Hoya polarizing filters that I have, there is a spring on top of the glass holding the glass in place. If you look around the edge you should see a small gap (about 3 mm) in the spring. I have removed the glass accidentally once or twice (by dropping the filter), so it should be possible to do on purpose. (Come to think of it, I actually assemled it wrong one time, so I had to remove the glass again, so I know that it's possible.)

Answer 2

I think photographically it's a rock now. But you can use it for doing things like polarizing source lights.