no, they are not continuous -- you lift and drop, which means that you are inserting a pin into a hole in a ring that in turn sets how far the ring turns before kicking over whatever lever holds the 2nd curtain back.
On the M-series leicas this is done with a cam and so speeds are continuous (except on some, such as the CL, which is continuous expect between 30 and 60 because that is where the slow speed train engages), but on the screw mount leicas and on the Contaxs, and on the Exaktas, there is no intermediate speeds.
When you speak of folding cameras, I think you are thinking of rim-set and dial-set compur shutters, which are totally different but also use cams, but the intermediate speeds would not be precise.
something to keep in mind with those old shutters on Contax/Leica/whatever -- they were rarely as precise as the markings on the shutter would have you believe -- that 1/1250 top speed on the Contax was mostly marketing hype. On any camera run a test roll to see what sort of results you get with whatever the camera is doing -- if all the shots are underexposed, for example, you know the shutter is running fast.
