This is topic Query from Home Theater Forum re: proj speed / shutter timing in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Robert Harris (Member # 1712) on 04-10-2004, 03:53 PM:
 
Hopefully this group can answer the following question posted to Home Theater Forum in regard to Phantom of the opera and all silent films in general:

"If the 1930 "International" version was shown at correct speeds, the 1925 footage would be shown at about 22fps and the 1929 sound retake footage at 24fps. Of course, audiences saw the 1925 version at whatever speed projectionists chose and 1929 audiences saw the film at a constant 24fps.


This raises a question that interests me. Perhaps someone out there can modernize my knowledge. Just how adaptable are modern cinema projectors regarding projection speed?

In my teens I frequented projection booths. In those days (the 60s) even projectors that went back to the silent era were strictly one-speed devices. In college I was the main projectionist for our public film series of art and historic films. It wasn't until several years after I graduated that they got 35mm, but the evening showings were in the hospital auditorium. It had a 15x20-ft screen with the industry-standard Altec Lansing speaker array behind. Both motorized curtains and dimmers on the stage lights and main house lights. 16mm aside, you could put on a professional show.

In the early years we had Bell and Howell auditorium projectors with arc lamps supplied by a separate generator. These machines were minimum adaptations of the B&H 300 series "classroom" projectors so you could run films at any speed you liked as long as you liked 16- or 24 fps.

Later we replaced these with a single French-made projector. It was a big machine that loaded from the port side instead of starboard and had a modern Xenon lamphouse. I had to bring the films to the booth (after cleaning them and preparing them for changeovers for the matinee performance at another location) and build them onto a single reel (5,000 feet if I remember right). Like those other professional projectors at real theaters, it ran at only sound speed. Period.

Our engineers had a special pulley machined for showing silents at 20 fps. It wasn't too difficult to switch from one to the other. Other speeds were discussed, but 20 fps was the most practical compromise. Their research into the literature together with some experimentation showed that to go lower than 20 fps, you would also have to change the shutter, which just wasn't practical.

To explain: A shutter serves two purposes in a projector. First, it eliminates travel ghost by blocking out the light when the film moves from one frame to the next. "Travel ghost" is a blur of white above or below bright objects in high contrast scenes. You see it occasionally in cinemas when the shutter is mistimed. There are even situations where you can see this effect in the natural world. (As a kid, I had a projector that didn't have a shutter, so there was a smear on all the intertitles of commercial home movies.)

The second purpose of a shutter is to reduce flicker. At the dawn of silents, many projectors had single-blade shutters which blocked the light only at the transition between frames. When a light or bright object turns off and on at or near sixteen times per second (16 Hz, the persistence-of-vision frequency), our eyes intepret that as flicker and, thus, the movies were called "flickers." If you turn the light on and off fast enough however, our eyes miss it altogether. We think the light is steady.

Professional sound projectors have two-bladed shutters so the light blinks at 48 Hz. Home projectors had three-blade shutters so a sound film blinked at 72 Hz and silents blinked at 48- or 54 Hz. 48 Hz isn't ideal. You can still see some flicker if you look for it, but 72 Hz makes the image a little dimmer, and light is at a premium when you're shooting to a cinema screen.

On the surface it would seem that lowering the projection speed and therefore the rate at which the shutter breaks the light beam wouldn't matter that much, but it does. Since our eyes are operating at a different rate (~16 Hz) there's an interaction between their behavior and what's happening on the screen. Some of the "frames" our eyes take in will see two interruptions of the shutter and some will see three, so some "frames" will appear darker than others. A pattern develops which gets interpreted as flicker.

In short, to show silent films at a wide choice of frame rates a projector needs to have both a means of altering the pulldown frequency and the shutter frequency. I would bet that the standard models have neither, but that the pulldown frequency could be altered to some degree by a knowledgeable service company. Do some cinemas have special equipment to handle silents or have modern technologies made it easier to adapt projectors for silent use?

Of course, this whole discussion begs the question of what is the "correct" speed. If I remember right, the Society of Motion Picture Engineers never quite got to the point of issuing a recommended standard (which would have then become an ASA [later ANSI] standard meant to be applied industry-wide). But there was a proposed standard on the table when sound came in and made the question moot. It called for a camera rate of 16 fps and a faster projection rate, I think 20, but I may be wrong. Most of those SMPE guys were cameramen and the proposal reflected their feeling that silents look more natural when projected a little fast. Or, maybe, just the reality that theater managers wanted to turn the house over fast."
 
Posted by Gordon McLeod (Member # 33) on 04-10-2004, 04:09 PM:
 
Speed control is fairly easy nowdays thanks to the use of frequency drive invertor motor controllers
Bodine Reliance/AllenBradley and many others make them they work very well some even have feedback to do positional lock between two machines
 
Posted by Robert Harris (Member # 1712) on 04-10-2004, 05:07 PM:
 
What is the relationship between speed and shutter set-up, or are the two unrelated?
 
Posted by Adam Martin (Member # 641) on 04-10-2004, 05:16 PM:
 
Despite the fact that frequency drives can easily add variable speed, you're simply not going to find this in a typical multiplex. At best, you'll find a machine that can do 24/25 fps.

You're going to have to go to a house that regularly screens specialty product in order to find a booth equipped to properly present these non-typical formats.

For additional information on variable speeds and their effects on picture and sound quality, do a forum search for "25 fps".
 
Posted by Gordon McLeod (Member # 33) on 04-10-2004, 06:36 PM:
 
Almost all European machines use invertors to control start up out of the box and most of those will support frequency control drive
 
Posted by Robert Harris (Member # 1712) on 04-10-2004, 08:47 PM:
 
Gordon...

I'm quite confident that you would know this.

As you change speed(for example from 24 down to 20), does one need to adjust the shutter, or does it remain at the same degree for all speeds?
 
Posted by Daryl C. W. O'Shea (Member # 1303) on 04-10-2004, 09:17 PM:
 
Since the shutter is directly tied to the rest of the gear train, any variation in speed will vary the shutter speed accordingly -- keeping the shutter in time with your pull down rate. No extra adjustment necessary.

The further below 24fps you go the more you'll be wanting to use a three blade shutter.
 
Posted by John Anastasio (Member # 607) on 04-10-2004, 09:31 PM:
 
Some 16mm machines such as the Graflex had a shutter controlled by a spring-loaded centrifugal device that automatically changed the two-bladed shutter to a three-bladed one when you slowed the machine to 16fps. I don't think that a 44hz flicker rate would be objectionable if you were projecting at 22fps. In fact, I doubt that you'd notice much of a difference at all. I'll bet that there's a SMPE paper on it way back in the archives.
 
Posted by Gordon McLeod (Member # 33) on 04-10-2004, 09:31 PM:
 
The shutter will maintain sync but if the machine has a fire shutter it will probably driop if it has a mechanical govenor on it below 20fps
 
Posted by Mark Gulbrandsen (Member # 72) on 04-10-2004, 10:54 PM:
 
Bob,

The shutter always has the same degree opening unless your projectors are fitted with a 2/3 blade shutter, which to my knowledge was only available on a few 16mm machines. What will change is the flicker duration since the shutter is running slower. I've run some silent stuff in the past and have found that below 22fps you need to install a three bladed shutter on the projector. At 20 to 21 fps with a two blade shutter the flicker would drive you insane in a short time. Below 20 with a two blade its actually difficult to look at the picture for very long, you'll get a bad headache from looking at it, especially if there are any bright scenes and assuming SMPTE screen brightness levels are kept constant.

You ought to try to watch a picture while doing front screen work at 18fl with a single blade shutter..... [eyes] [Eek!] [uhoh] [evil]

Mark

Its quite easy to adapt a variable speed drive motor to almost any projector!!

Mark
 
Posted by John Hawkinson (Member # 1135) on 04-11-2004, 09:19 AM:
 
I think it's worth combining the comments from Mark, Gordon, and Adam, because I'm not sure they are clear as they stand: There is essentially no deployed base of adjustable-speed 35mm projectors, but it is straightforward to modify most projectors to run at variable-speed by adding an invertor, aka variable-speed motor-drive controller, which any competant dealer should be able to handle.

I wonder if I remember rightly that Kinoton will sell you an adjustable-speed projector out-of-the-box?

--jhawk
 
Posted by Steve Guttag (Member # 268) on 04-11-2004, 10:17 AM:
 
What bizzar, old and forgotten formats...why that seems to be my specialty!
If you are really planning on showing silent films...then there really is but one choice in my book now...an "E" projector from Kinoton.
Their shutter spins at a constant rate (even whilst the projector is stopped).
As you adjust the speed of the projector (available with presets and with variable speed w/frame rate read out)...the flicker remains constant. The "E" projector can simulate a 2-wing or 3-wing shutter. When this effect occurs is also something that can be specified at the time of order. The standard machine will act as a 2-wing shutter from 20fps on up and a 3-wind shutter below 20fps.
Seeing one of these machines running silent film will make your jaw drop. It looks that good.
For those with Simplex or Century projectors...as others have mentioned, you can install 3-phase motors with controllers to vary the speed but many will recommend changing to a 3-wing shutter for the slower speeds if it is more than a one-shot interspursed between regular speed films. Also, watch out on your fire shutters as the speed drops ...they will also be closing down...Simplex had a different govenor spring for machines that were to run silent (available from Wolk).
Steve
 
Posted by Steve Kraus (Member # 476) on 04-11-2004, 10:38 AM:
 
Ah, but are you really recreating the silent film experience with high speed shuttering on low fps film?
 
Posted by Mark Gulbrandsen (Member # 72) on 04-11-2004, 11:22 AM:
 
Personally, I would still prefer a simple three bladed shutter on the machine... its easy to change out and its what would have been on the machine that originally ran the film eons ago. Of course you also have to have either a low intensity or early condensor arc to compliment that for the correct look.

Mark
 
Posted by Steve Guttag (Member # 268) on 04-11-2004, 08:34 PM:
 
I guess they didn't call them "flicks" for nothing!

Steve
 
Posted by David Favel (Member # 1125) on 04-12-2004, 12:31 AM:
 
Just finished an install on 2 x Vic 5
Can set the inverter to 51 Hz(or 24.5 fps), 52 Hz(25 fps)or leave as normal 50 Hz
Beautiful slow start up
 
Posted by William Hooper (Member # 71) on 04-12-2004, 03:49 AM:
 
To reinforce what JH said: you go into a booth, 99.9% of what you'll find is 24fps, 2 bladed shutter, not adjustable.

---------

From Ramsaye's _A Million & One Nights_ :
In 1895, the whole industry adopted Lumiere's (1894) 16 fps
Edison's Kinetoscope had previously been 48 fps
SMPE, 1925: 60 ft/min camera, 80 ft/min projector

Divide ft./min by 3.75 to get frames per second, that gives you 16 frames per second in the camera, 21.33 projector.

However, that's SMPE, & not the Real World:
"This rate is close to the average, and denotes the public's desire to have its picture drama injected under greater pressure with an increasing dose, bigger than life & one & a third times as fast. Theatre speeds of ninety to one hundred feet a minute are common.
[...]
"It is of interest to observe that a tachometer test of the rate of exposure used by the head cameraman of the Douglas Fairbanks studios in 1923 indicated a rate of twelve exposures per second for normal action. this would give a decided acceleration on the theatre screen, adding to the agility of the agile Fairbanks. Both Fairbanks & Charles Chaplin as masters of screen tempo are given to manuipulation of camera speeds."

David Shepard has some information about silent era camera & projection speeds at:
http://www.cinemaweb.com/silentfilm/bookshelf/#March1998
Also very useful is Brownlow's book _The Parade's Gone By_, which examines the very unstandardized & even incorrectly estimated speeds at which the pitchers were took & run.

http://www.cinemaweb.com/silentfilm/bookshelf/18_std21.htm

Is an example of speed non-concreteness is SMPE's 1928: 55 to 65 ft/min camera, 75 to 85 ft/min projector. That's 14.6 - 17.3 fps camera, 20 - 22.66 fps projector. But that's SMPE, & not the two *expected* things which governed speed: Notes in the cans, or the projectionists' estimation.

"According to Stanley Watkins, head engineer for Western Electric, he and his team checked with the Warner Theatre for the average speed of projection in 1926. They were told 'between eighty and ninety feet per minute' in the big theatres- between 20 and 24 fps- and around 26 fps in the smaller theatres. They settled on 90 feet a minute (24 fps) as a reasonable compromise for the Vitaphone process"

There was no expectation or application of universal, set projection speed; only instructions from the film maker, & otherwise the discretion of the operator, which in the
absence of factors like scheduling of shows varied by taste &
perception & was informed by professional judgment.

----------

As to what shutter goes on there:

The multi-blade shutter was the invention of Albert E. Smith in 1899 (Ramsaye).

Steve Kraus asks if it would be correct to show early silents with a 3-bladed shutter, mostly because what we've seen in junk rooms are old Simplexes with 2-blade bowties. The reason we see bowties is because they're from larger venues which needed the light. So you can run post-1899 silents with a 3-blade shutter & feel all period-correct. If you've got some VERY early stuff like the Lumieres' "Demolition of a Wall" or "Feeding the Baby", there could be some question as to whether if the intent is to show kindness to the viewers, perhaps you should gas them instead.

A 1910 Power's [sic] with 3 blade shutter, mostly installed in storefronts or portable!
-

A 1916 Motiograph with 3 blade shutter, still pre-movie-palace days:
-

By the time of the late 20s, we're up to big houses, 2 bladed shutters for light efficiency, Vitaphone, & the bowtie we all know:
-
There's a photo of the booth of the NYC Roxy here somewhere 2-bladed shutters, Vitaphone tables, they ran silents (Vitaphone just for shorts), big house, all possible light needed for screen.
[edit: here's the booth of the new Roxy]
-

And just because it seems appropriate, here's an aftermarket 1929 Pacent optical sound head:
-

The choice of a 2-blade or 3-blade shutter is not made just from flicker reduction, but from how much light you can afford to lose. A 3-blade shutter has less flicker, but less light efficiency - too much of a tradeoff in a big house.

I have two 16mm Pageants with the centrifugal shutter design that is 3-bladed at 16 fps & 2 bladed at 24 fps.
 
Posted by Larry Shaw (Member # 388) on 04-12-2004, 09:08 PM:
 
Steve,

Actually the higher speed machines (EG: ECII) go to virtual 1 blade above 40 FPS. Also, you can order the machines with the 3 to 2 blade changeover point at either 20 or 25 FPS.
 
Posted by Leo Enticknap (Member # 534) on 04-13-2004, 08:25 AM:
 
IMHO, the bottom line is that theatres which routinely screen archival prints and rep programming are likely to be equipped to show all speeds from 16-30fps without any flicker, usually with a combination of a three-bladed shutter and an inverter fitted to the motor. If you're planning a new installation from scratch and factoring archive and rep into the spec, then the choice of projector is crucial. The characteristics I would look for are:

For me it would be a toss-up between a Vic 5 and an FPXX in most scenarios.
It's the temporary venues and occasional one-off festival screenings in, say, a multiplex that are the problem. As others have noted, these are likely to have no inverter (i.e. the projectors will only run at 24fps), a two-blade shutter to maximise light output and only have the plates and lenses for 1:1.85 and 'scope. Many venues will also have only one projector available, thereby requiring the print to be plattered: something which no archive approves of and many ban outright. The necessary extras to show silent prints at the correct speed and ratio can be installed very straightforwardly: it all boils down to money.
 
Posted by Frank Angel (Member # 248) on 04-14-2004, 08:03 AM:
 
You also need to determine the precise nature of the cinema's expressed mission. What does it purport to be? Is this one of the many booths in a multiplex that plans to run some alternative titles some of which will be the occasional re-released silent? Or is it a commercial art house that may, on occasion, run a few silents or may even mount a series of silent titles which are taken from the available re-releases and restorations that are readily made accessible through regular distribution houses? On the other hand, are we talking about a theatre that is attached to a museum or housed in the Film Department complex of a major university which specializes in motion pictures of the silent era and who have their own archival print library of rare and original titles? The point being that to install a lot of expensive, very specialized equipment for the occasional silent film engagement of a title that is re-released by a studio, well this might be overkill. The reason being that those re-released titles, in all likelihood, will have been optically converted to sound format by randomly step-printing additional frames to bring it up to sound speed and also optically repositioned and resized to the standard sound format frame. This is done with many of the popular silent titles. These converted prints need no speed adjustments and no special plates or lenses nor does the image need to be recentered on the screen as would be the case for original silent prints.

Occasionally you will find some re-releases made where there is no conversion at all, they are simply direct copies onto new 35mm stock; in such cases, yes, you will need to vary speed and used silent aperture plates and shift the centerline on the screen, but even that might not require the installation of a variable speed motor. When we came upon such a contingency, we changed the gear pitch of the soundhead transmission gears to reduce the speed from 24 to 18 and it worked just fine. Flicker was a bit of a problem at first, but we cut back the light a bit and that seemed to be a viable fix; everyone was happy.

However, for really SERIOUS venues, like, say, MOMA or FILM ARCHIVES in NYC for example, which specialize in rare and often times original prints which they play regularly from their own vaults, such a venue would have to be designed with this in mind, making a serious commitment to a complete system that will properly play the silent format. This would including all the points detailed above, save one which I will add -- you will also have to build a nitrate certified booth, since if you are regularly running vintage prints rather than restored/sound converted prints, you certainly will encounter nitrate base material. All the speed controls and shutter adaptability will not help one nit if the booth is not constructed to meet all the safety and code requirements attendant to running nitrate prints.

Everthing depends on the overall mission of the cinema -- what does the cinema want to be.
 




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