Two lenses lock into the caddy, so they're ready to attach to your camera when you need them. The framer is fairly large, about the size of the closeup framer for the Nikonos. The framer has only one post, for better maneuvering. The conversion lens fits in front of the standard lens underwater. It the caddy is occupied by your 20 mm conversion lens, note that the macro framer folds up small enough to slide into a BC pocket.
Macro photos are probably the easiest scuba pictures to master.
With the camera set properly, and the strobe on TTL, you just surround some sea critter with the framer and click the shutter. It's easy to miss the framer with the flash. If the nudibranch wasn't on fire after the flash died away, I knew I hadn't gotten a good exposure. For serious macro work, you really need two strobes. If you keep the strobe on the mount, the aim should be double-checked periodically.