Eclair ACL S-16 Shutter --- one person's opinion

[Mark <super16acl@aol.com>]

In the end, everyone goes with what works best for them. Some folks take 
Pentium 500 computers and overclock them .. 550 ... 600... 650 ...700. Where 
is the "grey-line" that you can get away with, versus risking incorrect 
output or a crash? For some people it is 500 --- if they need a 550, they'll 
buy a Factory 550. For many, or perhaps most,  it may be that overclocking to 
550 seems well within tolerance. A smaller group of folks like to push the 
envelop to see what they can get by with by installing special super-cooling 
fans, and they'll see how many days the system can run with 
processor-intensive software without making a mistake or crashing, and then 
they'll use the computer knowing the maximum period of time that it can go 
until it needs to be shut down and cooled. None of them is right or wrong. 
Each does what makes sense for them.

The Eclair factory specs in R-16 call for the timing of the shutter and 
mirror to be such that when the shutter is open, the mirror is not blocking 
any part of the exposed film. Modifying or Replacing the R-16 Shutter with a 
S-16 Shutter that has a smaller angle (to give the mirror the extra time to 
clear the wider aperture) is a prudent extension of the basic Eclair ACL R-16 
specs to the S-16 format. 

The number 144 is not etched in stone. At 24fps, it was the next number in 
line after 175 that yielded an "industry standard" exposure time (1/60th), so 
that's what I went with in designing the HD-144 shutter. It is 1/3rd of a 
stop difference. (As fate would have it, there is also an advantage when 
shooting an NTSC TV screen,  and the timing of the pulldown claw has a 
slightly greater tolerance for error, but those are just small fringe 
benefits).

144 degrees is on the conservative side; 175 degrees just barely lets the 
mirror clear in Regular-16.  So where is the "grey-line"?  What is the 
equivalent of a "Factory Spec" Shutter Angle for S-16? Here is where 
qualified people may have a valid diversity of opinions, and then it is up to 
each user to determine his or her needs. My answer was 144. 

For a student film or short just struggling to get by financially, specs may 
be far less of a concern as long as the film gets made, and that's 
understandable. At that level you could also get by with not recentering the 
lens flange just by staying on a 25mm lens. Indeed, just taking a file and 
opening up the size of the frame in the aperture plate will also work if you 
are careful to keep the track support very clean and free of static charge. 
And I don't say any of this with sarcasm --- a decade ago I did it that way, 
and it cost nothing.

For me personally, not adjusting the shutter angle by a certain amount to 
reflect the aperture modification is dropping too far below specs for the ACL 
to be considered a viable camera of equal quality to the Arri SR and the 
Aaton.  I'd really urge anyone with 175 degree shutter in their S-16 ACL to 
spend a hundred dollars and ask your Tech to glue in a very thin piece of 
metal to close it down enough to let the mirror clear. Keep the S-16 ACL 
above the "grey-line."

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