Recently I've been experimenting with my Polaroid Spectra filters again. I love cheap camera tricks, anything to make the world more whimsical and match the fairy tale in my head. In the past I've only tried these with their original devise... and then on cameras with smaller lenses, assuming they wouldn't work on my SLR, wrong! This morning i played with my filter set for a bit near a window and what a delightful result! I just got this new wide angle lens and they worked beautifully being held in front of it. (As far as the Canon EF 28mm f/2.8 Lens goes, I'm not sure if I would recommend it yet. It's still fairly new in my possession and I'm still figuring it out, I bought it for event photography... day job.)
I did a quick search, and you can still find these neat Spectra Lenses on Ebay!... not as cheap as when i found mine 5 years ago, but way cheaper than a new camera lens! Observe here, here, & here.