I think the 285 has the same connection as the 283 -- and several other Vivitar flashes. It's a standard PC connection on one end (for the camera or lens/shutter) and a pointed plug on the other (for the flash) which connects in a hole on the side of the flash shoe. The cord that comes with the Vivitar flash is short (8"???), but long enough if the flash is on the camera's flash shoe. If the flash is off-camera, you need a standard PC-to-PC extension cord to use with the short Vivitar flash cord (or one of the extension cords that Vivitar sold).
Vivitar and others used this push-in, pointed connection -- maybe there is a term for it. I call it a Vivitar flash connection. There are similar pointed connectors that look the same, but don't fit -- just to confuse us.