Tiffen Photar Series IX red-green-blue colour filter set
This is a set of three Series IX filters ideal for trichrome photography. The #29 red, #74 green, and #47 blue have very narrow bandpass characteristics for better colour separation. These are Series filters, so they don’t have threads to attach to a lens: you’ll need a Series IX holder (not included) or get used to just holding them in front of your lens. They’re approximately 80mm diameter.