'Double Shutter' Century's

[Jacob Tutt]

Hi Film Tech, I've recently come across a pair of Century CC machines. They also have water-cooled gates installed. I'm wondering...

What is the main advantage of a double shutter Century, versus a single shutter?
It looks like the blades on each shutter are smaller than the blades used on a single shutter mech. So my initial thought is more light or something to do with reducing flicker?
Are there any apparent pros and cons to a Double Shutter Century versus a single Shutter Century?

Jacob

[Steve Guttag]

Double shutter will have more light. As you noted, the blades are shorter. Furthermore, since they are counter-rotating, they close the aperture off twice as fast and open the aperture twice as fast...that time is turned into extra light.

However, all is not free there. The close the center of the aperture last and open it first...so...the light develops a hot-spot, of sorts but it is brighter in the middle of the screen and more of a hot line than a spot. The next down side is that there is inherent gear lash in all geared things. Since the two shutters have a different set of gears to go through (driven off of a common vertical shaft but the reversing shutter gets another set of gears...so they are going to bounce (and all shutters bounce...use a strobe light and you'll see just how un-uniform shutter rotation is)...but with counter-rotating shutters, you'll have a moving target where the shutters meet/separate. This will appear to be a flicker on screen. Lightweight aluminum shutters will have a more violent bounce. Heavier steel shutters will have more of a meandering bounce. If you look in the spot sight glass, you'll see the line where they meet/separate and see the bounce there too. If you need the light, they are one of the tools to use. If you don't, they are less desirable.

[Jim Cassedy]

All the 70mm machines I've worked with have double shutters, I assumed due to the need
to cut off the light quicker at the larger aperture. I haven't noticed the other artifacts Steve
mentions, but that's not to say they aren't there. I like the idea of taking a look at the
revolving shutters with a strobe light to see the 'bounce' I'll have to try that some time!

Fortunately, I've never had to time a dual-shutter mechanism, other than slightly touching
them up a bit with the adjustment knob on the front (or sometimes on top)of the projector.
All the 70mm projectors I've encountered were Century "JJ"'s, except I did fill in one night
about 25years ago at a theater that had one of the Simplex-70's. I can't recall if that proj
had double shutters- - but I do remember that the image having a small amount of vertical
jitter. It was a change-over system & both projectors had the the same jitter, so I assumed
that it was just flaw in the design of that projector. (Which I think was nothing more than a
regular Simplex XL that had been "up-sized" to 70mm)

[Steve Guttag]

Of all of the 70mm projectors in popular use...the only ones that I can think of that used double shutters was the Century JJ (the double letter denotes double shutter...like CC and HH...then they screwed that up when the SA/DA came out and ORC made it even dumber with the JJ2-S....they should have just called it the J2 (or J3) and the Kinoton FP75E. The DP75, Vic8, P70, Simplex 35/70, Ballantyne "Pro" 70 all used dual wing (single) shutters. The DP70/AAII used a single wing, double-speed shutter.

The JJ used double shutters for more light, not the taller frame, though that didn't help the Century cause. Century was inefficient with light. Any shutter less than 90-degrees on a Century 35mm would ghost whereas a Simplex could use an 84-degree shutter, comfortably. Yes, moving to 70mm would necessitate a taller blade for a Century JJ2-S. Somewhere, I have what the JJ2-S shutter blade dimensions were. ORC also changed the double shutter blade so it had more of a diamond cut to it...which would make it more hot spotty but also get a bit more light in the middle.

[John Eickhof]

I never experienced flicker or hot spots on any double shutter machines, even with the largest of lamps behind them. The CC & HH did seem to perform better maybe due to the cast gate and trap assemblies and all steel fixed curved and straight water traps. the engineering behind them was an attempt at a simple 'double dissolving cutoff' of the light beam, supposably making a smoother flicker less image. I do agree the diamond shaped shutters appeared to pass more light (and heat) onto the lens though causing focus problems unless the spot was very flat on the aperture, I think the brenkert heads were probably the best 35mm double shutter machines, they had a shaft within a shaft drive like the century but a better heavier design with better heat dissipation. (the small bearings on the century shaft drive housing failed often from heat dissipation from the black colored aluminum shutter blade) The brenkert shutters cut at an angle so they dissolved the light in a horizontal plane from top and bottom and were made of heavy gage sheet steel and they were geared with an umbrella shaped spiral bevel gear with only one gear contact per blade keeping backlash to a minimum, where the century had three gear contacts between the two shutters so backlash was more troublesome and gear wear plus shaft endplay made more slop possible I have had occasion to have to use 92 degree shutters on century single shutter machines to get rid of ghost on indoor screens with large lamps, and stripped shutter gears on JJs that inexperienced operator/managers (typically UA & Syufy) after melting and warped shutters interfered with each other or housing clearance!.

[Steve Guttag]

Just like with changeover cues, if I ever point the flicker of double-shutters out to you, you'll never not see it again. I worked with double shutters on Century projectors a long time. They have their ups and downs, like everything else. I never had particular bearing problems though. GR-207 wear could be, if the "projectionists" didn't keep the gears lubed or the steel gear got ribs in it.

[John Eickhof]

i have only really noticed picture problems with the da but i attribute that to the poor trap design and invariable incorrect tension set up by the lens holder, the backlash comes from the double shutter transfer gearing on the C1-D-55 assy particularly the BG-10 bearing and unlubricated gear in the assy. the double shutters were normally 72 degree but Wolk did make some 75 degree replacements to help eliminate the condition. I am sure you are correct in your description of the flicker, I think I used the put it in as ghosting in the day, I too rebuilt hundreds of centurys through the years right up to over 120 new or recently installed ORC centurys in the western states that had problems right out of the box after ORC started making hem on the west coast and had ceased casting in New York! I still prefer the workmanship of the early C and H models over the A model. However the 8 G models I refurbished for Larry Little were probably the worst ones I have ever seen. They were a model H with a half width shutter housing, straight C trap and H style 4" lens holder with focus knob at 90 degrees from picture axis! They were model G-1 built for the Link gunnery trainers in WW2 I installed them in an 8 screen in Las Vegas on RCA 9030s back in the early 1980s, if the shutter got bent or warped at all it would hit the housing! I have one in my museum, it has four cast bosses on the front with 1/2" npt for mounting in the trainer frame!

[Steve Guttag]

Cool!

I saw some double shutters for drive ins that were barely blades at all. I'd be amazed if they were more than 10-20 degrees each. I liked the JJ's 35mm trap well enough...it definitely did better than the SA/DA. I was never jazzed about the back-flip the Century does on the upper loop.

[Mark Gulbrandsen]

Cool!

I saw some double shutters for drive ins that were barely blades at all. I'd be amazed if they were more than 10-20 degrees each. I liked the JJ's 35mm trap well enough...it definitely did better than the SA/DA. I was never jazzed about the back-flip the Century does on the upper loop.

The back flip in the upper loop was never a problem for me. while running dailies on modified C's for about 15 years, some times a million feet of dailies per show, and where the splices were always single sided. Not one film break or malfunction because of it. Ditto on the VistaVision projector, which in my case was built out of a Model H and a modified Cinerama straight gate. I did dislike the solid trap in the H Series and was glad they were not sold for very long. The 35/55mm projector, model EE also had the solid curved runners as well as an accelerated pull down intermittent. The later bands make way more sense as they are self equalizing.

[Jacob Tutt]

Thanks everyone for sharing your thoughts!

If I were to put these projectors to use they would be set up in a theatre with a 30ft screen. I think the digi has a 2k lamp by comparison.

So if I'm lighting a 30ft screen without an urgent need for more light, is it possible to remove the gearing for the second shutter and just install a larger single shutter with 90-degree blades? Or would I be better off replacing the whole shutter shaft assembly? I suppose I could make that decision after I have seen the effect the double shutter creates.

The projectors have water-cooled gates and I don't think they will be necessary for this theatre. I'm assuming I could use the gate as I normally would, just without any water hookups. Any comments on this front?

Thanks all,

Jacob

[John Eickhof]

I would say set it up and see what you think, if you want to go to single shutter I have the parts for easy conversion pm me. Mark, I have only seen one EE head it was many years ago, It was on an emergency call in a Syufy house in the bay area, seems the operator replaced the int. spkt with a 55mm ! where the machine had been converted to full 70! had a little sprrocket hole damage on the print and he int shoe did some damage to the mag tracks...oh well, typical Syufy problems!

[Jim Cassedy]

John- I have seen double shutter centurys that were converted to single shutter, but
I don't have any idea of the mechanics of doing so. But it apparently can be done.
- - and yes, you can use a water trap gate without any water. I've worked at dozens
of theaters that had water cooled gates that weren't hooked up.

[Don Furr]

I had a double shutter Century that I converted to single shutter. I don't remember it being hat hard to do.
Question: Was there ever a 35/70mm double shutter?

[Mark Gulbrandsen]

I had a double shutter Century that I converted to single shutter. I don't remember it being hat hard to do.
Question: Was there ever a 35/70mm double shutter?

Yes, That's why the double letters. "JJ", "CC", "HH" and so on designate double shutters. "C", "H", etc. are single shutters. The edition of a "W" in there with the others designates water cooling.

[Mark Gulbrandsen]

Now all of you can say that you've seen the elusive 35/55 Century. There was a pair of them at the State Lake Theater in Chicago back in the day. Those ended up at Charlie Wolk's shops. The most I ever had of one of these was an intermittent with dual gauge sprocket.