Well, I removed a 3.5 E camera having the Rolleikin counter knob installed and pulled another Rolleikin storage case with a complete and uninstalled Rolleikin. The case on this latter model Rolleikin was a leather one (vs the black metal case) and had 2.8 marked on it. Here are the differences I noted: **One counter knob had a black scale w/white numbers and the other was polished aluminum with black numbers. **One had a mask designed for the F model and intended to be inserted under the screen vs the older masks designed to be placed on top of the screen. They both contained the earlier E model mask, however. Are there any mechanical or incompatability issues regarding the application of these Rolleikin sets? Does it matter whether these pieces are installed on an E or F 3.5 or 2.8? Best, Steve