Just signed up here because I ran across this thread *after* doing full services to two IIa's and wish I had this info prior. I found out through trial and error the very counter intuitive fact that decreasing tension actually increases effective top speeds. Do you understand how? Because I certainly don't. It would be very helpful to understanding these weird designs.
Also, did Henry clarify why a modern tester would read the 1250 speed wrong? As far as I can tell, these do in fact work like normal modern shutters, in that they have a fixed high speed travel time and use variable slit width to make different effective speeds. Is that not actually correct? The full gate can't possibly be open for only 1/1250, the curtain speeds are way too slow. I was able to fix 1250 traveling closed by simply delaying second curtain open (i.e. enlarging the slit width) via the first curtain cam. Once that was done, that led down the rabbit hole of finding proper tension and finding that the camera's (very high) current tension setting was only yielding 1/300 at 1250 - something I noticed Henry mentions being a common problem with previously serviced cameras sent to him. What I can't understand is *why* significantly less tension actually sped it back up to 1/1000 on my tester - all while having no meaningfully negative impact on medium and low speeds.
