Each back model has its dedicated plate for a certain camera platform.
e.g., the Sinarbacks eMotion series (22, 54, 75) use a certain adapter plate for the use on the Sinar Hy6. When one then wishes to change to a e.g. Contax 645, one has simply to get the eMotion/Contax 645 adapter, unscrew 3 screws and mount the Contax adapter. This takes 2 minutes, at the very maximum.
You DO NOT have to buy a new back!: the very same back can/is used on different camera platforms.
Best regards,
Thierry
I find it neat that they are made at all. Many other manufacturers have no plates, and you must pay $3000 to change the mount! Sinar's method is great, in comparison. I presume you simply buy an (expensive) plate for the first back, and forever after you keep it and just buy new backs, right?