S-16 144 Degree Shutter

The HD-144 Shutter took a great deal of R&D, as it improves upon the original design in several ways: where the Regular-16 Shutter was made of 3 pieces glued together, (the brass piece on the “open” side of the shutter acting as counterweight), the HD-144 Shutter is manufactured as a single piece, with brass counterweighting mounted on-board to create greater rigidity in the entire structure. A major source of noise in old, unserviced ACLs comes from a warped shutter scraping the Base Plate, Mirror or underside of the Ground Glass Mount.

HD-144 Shutter before painting (Left)
Regular 16 Shutter (Right)

The Regular-16 shutter opening was 175 degrees (1/49 second exposure @ 24fps); the Super-16 version is open 144 degrees (1/60 second exposure) – necessary to allow the oscillating reflex mirror extra time to clear the extended width of the wider Super-16 aperture. As a result, light meter readings should be taken at 1/60 second. This is a 1/3rd stop difference.

There are also several side-benefits that come along with the 144 degree angle:

1. Images photographed with the HD-144 will be ever so slightly sharper because of the faster Shutter speed; on the other hand, this shutter speed, and focal plane shutter (as seen in Panaflexes and Bolexes) reduce the jitter compared that 45-degree (not shutter speed!) seated mirror shutters on fast pans and tilts.
2. An NTSC TV photographed @ 24 fps will have negligible roll bar.

The Shutter should just drop into place overtop of the Shutter Axle (MIN 42). Slight variations of a fraction-of-a-millimeter in diameter of manufacture of the shutter axle from batch to batch could result in the opening of the Shutter  being too tight. If this is the case, gently run a rounded file evenly around and into the opening of the Shutter — it will not take much scraping for the Shutter to suddenly fit. Be very careful not to warp the Shutter while handling.

The HD-144 Shutter has two brass pieces attached in order to best balance the Shutter. NO TWO ACL MIRRORS will clear these brass pieces in exactly the same way, and it will be necessary for your Tech to take a file and gently work away any brass areas that may be coming into contact with your camera’s Mirror. With some cameras, a deep groove may need to be made in the cylindrical brass piece attached to the hub* (* or the very top edge of the mirror can be filed down a fraction of a millimeter) in order for the top of the Mirror to clear without scraping, (use a small, round file). In other cases the various levels of the large brass counterweight may need to be shaved slightly to allow for increased Mirror clearance, or for the Ground Glass to come a little lower without scraping the Shutter. This final customizing can only be done in the actual camera, and really isn’t too time consuming — it will be quite obvious where the danger zones are. DO NOT RUN THE CAMERA until this work has been done!

Above Left: The HD-144 Shutter is one solid piece , with two precisely carved brass counterbalances
Above Right: The original Regular-16 Eclair design was in 3 pieces

A frequent cause of camera noise is from a Shutter scraping the Base Plate or the underside of the Ground Glass Support Block. Sometimes it can take hours of painstaking work to correct this, although the improved stability of the HD-144 Shutter should make this adjustment less time-consuming than it has ever been. Still, to get a Shutter to be absolutely quiet will still involve a certain amount of good old-fashioned bending. But be very subtle, it doesn’t take much to make a big difference. If you can “feel” the metal bend, you are applying far too much pressure!

Setting the correct timing between the shutter, pull-down claw and mirror is critical.

It is recommended that the Shutter be painted a very flat black.

Re-Balancing the Shutter

One of the challenges in designing a Super-16 Shutter that balances well is the fact that slightly more counterweight is needed than with the Regular-16 Shutter because of the added weight of the extra metal used to close the Shutter to 144 degrees, and yet less room is available because part of the Shutter must be cut away in order to expose the entire width of the Super-16 frame. That is why the counterbalance has been built ‘upwards.’

After filing the brass counterbalance to work correctly with your camera’s mirror, it will still very likely be balanced well-enough to run just fine. However if camera vibration occurs with the HD-144 Shutter that wasn’t already occurring with the Regular-16 Shutter (there is always a little vibration when the ACL runs), the best solution is to send the Shutter to a “Balancing Company” (listed in the Yellow Pages under “Balancing”), and for a very reasonable charge they can put the Shutter on a high-tech machine to check the balance with 100% accuracy, and then correct any imbalance by attaching some lead flakes with epoxy to areas of the Shutter that your Tech specifies as being “in the clear”. The upper area of the brass cylinder is a good candidate spot. (Even if no brass is removed at all, it is still a good idea to send the Shutter to be re-balanced, because without any filing done it is possible that a little brass might need to be scraped rather than lead added.)

Be sure to note special considerations for S-16 ACLs to be used in Europe