The TP-88EC Prism Unit from Kowa is an adapter that allows you to easily convert your TP-556 Prominar 500mm f/5.6 telephoto lens into a spotting scope. Attach the prism unit and a user-supplied TSN-880 or 770 series-compatible eyepiece, and you have a full-functioning medium/long-range spotter that offers a bright, sharp image thanks to the premium Prominar lens optics. The prism unit can also be used with the separately sold TSN-EC3 eyepiece converter to utilize TSN-660 and 600 series spotting scope eyepieces.