OIII Filter - what's it do?

I see OIII filters for sale everywhere, but no descriptions. What's it's purpose? I have a Tak FS-102 and a C9.25...would an OIII filter enhance my viewing with either or both of these scopes?

Thanks,

-Phil (aka Filter-Challenged)

It filters out more or less the entire visible light spectrum except a very narrow spectral range of visible light. That range is centered around the OIII wavelength (500 some odd angstroms). This filter may drastically improve your images of some specific nebulae, but it will make everything else worse.

They're quite expensive, especially considering their limited usefulness, but for the nebulae on which they work, they really do work.

Thanks Dan, Russell, and John. I'll try out a Narrow-band filter instead.

-Phil