John, Not only a different inter lens spacing, but a different bayonet lug orientation on the taking lens. Jerry John Lehman wrote: > From: Jerry Lehrer <jerryleh@xxxxxxxxxxx> wrote: > > > Now does anyone out there know which kind of cap was > > originally on the 2.8A Rollei? It was not a Bay III cap. Evans > > shows a Bay II mirror cap. > > Mine has a mirrored cap. It is bay II, with different interlens spacing > than the later Bay II cameras.