European S-16 Conversion

Typically, shutter conversion for the S-16 ACL isn’t done in Europe or a country using 50 cycle power.  With 50 cycles, a shutter angle of 172.8 degrees is needed for HMIs (and to shoot off PAL TVs) — this gives a shutter speed of 1/50th at 24 fps, matching the 50 AC cycles — whereas in the USA with 60cycles, 144 degrees gives a 1/60th shutter speed at 24 fps, which will work for HMIs and NTSC TVs (HMIs also work at 24 fps under 60 cycles with a 180 degree shutter).

European ACL users have the conflict that ideally a S-16 ACL’s shutter should be closed down somewhat to allow the ACL’s oscillating mirror time to cross the extra width of the S-16 frame … but to do that would create a problem syncing with 50 cycle power for HMIs. (The Arri and Aaton don’t present this difficulty because they don’t use an oscillating mirror design as does the ACL).

Therefore if someone from Europe is sending an ACL to America for a conversion, or if someone from America is sending an ACL to Europe for a conversion, it is necessary to discuss with your  Tech if you will be shooting under HMIs and under what type of power, to determine how best to approach the shutter issue. While technically a shutter angle of 172.8 is less than theoretically ideal for an ACL S-16 conversion, there may simply be no other option for someone shooting in Europe with HMIs. (In such a case, re-centering of the mirror … considered optional for American S-16 conversions of an ACL … is probably more critical when the shutter angle is not modified, in order to eliminate any extra uneven exposure of the right edge, even if miniscule. Consult with your Tech).