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Topic: 2nd shutter blade on a SIMPLEX

John Eickhof
Jedi Master Film Handler

Posts: 588
From: Wendell, ID USA
Registered: Jan 2000

posted 10-18-2000 11:00 PM

The three blade shutter for an E7 or simular projector is actually cut at about 100 degrees on all three blades, the three openings are approx. 20 degrees each, Thus, the light is scanned across the open aperture
making the picture even more flickerless.
The light loss is substantial though, and generally twice the recommended wattage
for academy brilliance is required. Conical shutters (like the XL) are cut at about 75 degrees closed with the openings being 45 degrees each, this is possible due to the shutter blade being so close to the film,
thus the efficiency is much greater and only
about 55 degrees of closed shutter are required to block the pull down. That is why a Simplex XL will put more light through the film than any other american made machine including the Christie. I stock 3 blade XL shutters too, but they are quite pricy!

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Sean M. Grimes
Expert Film Handler

Posts: 247
From: Lunenburg, MA
Registered: Apr 2000

posted 10-19-2000 03:13 AM

but how does the light on screen of an xl compare to a 1060? I mean is the design really at all comparable?

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Dennis Atkinson
Expert Film Handler

Posts: 129
From: Birch Run Michigan
Registered: Feb 2000

posted 10-19-2000 08:20 AM

Having worked with 3 bladed XL's in the past, the light output is cut by about 1/3.
With some other changes you can show silent films at 16fps with no flicker, which is why the 3 blade was needed in my case.

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Pete Lawrence
Expert Film Handler

Posts: 192
From: Middleburg, PA
Registered: Aug 1999

posted 10-19-2000 07:26 PM

Using John's numbers, that says about 16.7% of the light reaches the film, 83.3% is completely wasted. This sounds like something that was designed by a government bureaucrat.

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Jon Bartow
Master Film Handler

Posts: 287
From: Massachusetts
Registered: Nov 1999

posted 10-20-2000 10:10 AM

Perhaps the illustrius John Pytlak can correct me on this, but I seem to remember that three bladed shutters are also used in Film to video transfer

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 10-20-2000 10:40 AM

Actually, film-chain projectors use five-bladed shutters. This results in 120 flashes per second, which is easily divided by 30fps, which is the frame rate for NTSC television (actually, it's 59.94 "fields" per second, but it's close enough that there's no flicker when showing a film on television). PAL (European) television runs at 25fps; usually, films are just run slightly fast when shown on PAL television and the sound is usually processed sufficiently to make it sound fairly normal. Films intended for broadcast on PAL TV systems (documentaries, etc.; stuff that wouldn't be released theatrically) are often shot at 25fps. Some films work intended for NTSC television (commercials, etc.; again, stuff that won't be shown theatircally) is shot at 29.97 or 30fps in order to look "smooth" when transferred and to avoid the motion artifacts that one normally sees when watching 24fps film on NTSC television.

Now, most TV transfers are done on a "flying-spot scanner" rather than with an actual projector with an intermittent movement. I've never seen a 35mm film-chain projector and have sometimes wondered about what kind of intermittent movement they use--surely, it would have to be something along the lines of the "drive-in" fast pulldown type...

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Jeff Moore
Film Handler

Posts: 7
From: Lakewood, CA, USA
Registered: Sep 2000

posted 10-20-2000 12:16 PM

Scott, What exactly is a "flying spot scanner", and how does it differ from a regular telecine? By the way, thank to everybody for the answer!

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 10-30-2000 12:04 PM

Information on "flying spot scanners" may still be found on the Cintel website:
http://www.cintel.co.uk/

In general, these telecines scan the film with light generated by a cathode ray tube (CRT), and convert it to an electrical signal using color filters and photomultiplier tubes.

Most books and faq's about film on television contain a description of telecine technology, both flying-spot and CCD.

As far as shutters, the shutter blade(s) need to block the light while the film is moving during pulldown, otherwise, you will see a streaking known as "travel ghost". For the most commonly used 4:1 "Geneva" or "Maltese Cross" intermittent, the shutter blade needs to be near 90-degrees, depending on how efficient the shutter is in "cutting" the light. At 24fps, only one interruption per frame would give very unacceptable flicker, so a second "flicker" blade (or two rotations of a single blade) are usually used to give two interruptions per frame, or 48 per second. For two 90-degree blades, the shutter efficiency is about 50 percent. To completely eliminate flicker, an even higher frame rate is needed, or a third blade can be used on the shutter to give 72 interruptions per second at 24fps. Three 90-degree blades are only 25 percent efficient --- that is, you only get half the light compared to a two-blade shutter.

As discussed in another thread, three-blade shutters almost completely eliminate flicker, and would certainly be an advantage on small or medium sized screens, where the lower efficiency can be compensated for by a larger lamp.

For silent films (16fps), a three-blade shutter is needed to achieve acceptable flicker (3 x 16fps = 48 interruptions per second).

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

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