There are loads of filters: polarizers, variable NDs, UV filters, and more. But at the end of April, a new Kickstarter will be launching for Mount July Filters. These are filters that go onto the front of your lens and add a bit of cross processed fun to them. From the press release, they seem to have a variable effect that can spin around just like a variable ND in a way. You’ll be able to stack them on top of one another for even more different effects–though we’re not sure how much it will cut down on the image quality.
The company is stating that the filters are multi-coated with resin for low diffraction and that the ring itself is made from aluminum. Most filters are made from aluminum, but the reason why some brands (such as B+W filters) are so expensive is because they’re made from brass.
Once they launch, they’ll be available for under $30 each. I’m personally curious about how these might work when you add in a flash (which is generally daylight balanced) and then gel the strobe.