Dave Bird

Speaking of Shutters & Parts....

AFAIK, projectors intended for telecine (film-to-video) use a FIVE blade shutter, along with a special fast pulldown, to achieve the 3:2 pulldown frame rate conversion from 24 fps film to 30 fps video without flicker.

3-blade shutters are widely used in screening rooms, to almost completely eliminate any perception of shutter flicker (3 x 24 = 72 interruptions per second, so flicker is much less visible). A 3-blade shutter can also be used in theatre applications to minimize flicker, as long as you have enough light to overcome the lower shutter efficiency. Using a 3-blade shutter to minimize flicker, I've projected prints at light levels up to 60 footlamberts on a smaller screen, and they look stunning. The current screen luminance standard of 16 footlamberts specified by SMPTE 196M (with an allowed range of 12-22 fL for theatres) was primarily driven by the need to reduce flicker perception with a 2-blade shutter having only 48 interruptions per second.

For a home theatre with a small screen, and excess light, using a 3-blade shutter would offer the advantage of almost no flicker, and the ability to increase the light level well above 16 footlamberts, to see that "brighter is better" usually produces stunning images.

Of course, when showing silent films at 16 fps, a three-blade shutter must be used, since flicker with a two-blade shutter would be very annoying.

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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

Also, is the "hub" of the conical shutter on the XL part of or seperate from the blade itself? (One of mine is cracked, will I replace the whole blade or just a hub piece? I can't tell from the parts diagram.)
Thank you for the replies.

I don't want to say rust, but the pitting in that area of the projector made it a little difficult to disassemble the c/o zipper dowser from the cable. Before I re-attach them, what can I use to protect these little allen screws from sticking next time. Or is it such a high heat area (and so rare that you'd need to get the cable out) that I should forget it? What will clean the (very slight) pitting in this area? Thank you.

A conventional 4:1 "Geneva" intermittent using a maltese cross movement requires a nominal shutter blade of 90-degrees to block the light during the film pulldown. (See Tim Reed's excellent animated video of how an intermittent works in the "Videos" section of Film-Tech). Otherwise, light going through the film while it is moving will cause "travel ghost" on the screen. With the low light levels typical in a drive-in, a shutter blade under 90 degrees might be used to gain slightly more efficiency at the expense of a bit of travel ghost.

Special high speed "drive-in" intermittents used an extra mechanical linkage to decrease the pulldown time. A 5:1 high speed intermittent could advance the frame in only about 72-degrees (360/5 = 72). So the shutter blades used with these intermittents could be as small as about 72 degrees, putting even more light on the screen. The disadvantage of the high speed intermittents was that the extra linkage made them noisier and more problematic. The higher film accelerations also put more stress on the film perforations, which was more of an issue on triacetate prints than today's tough polyester prints.

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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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Mark: When you saw the improved definition and steadiness, could it be that you were using it with 90-degree shutter blades? If the film was pulled into position within 72 degrees, it would have more time to stabilize in the gate before the shutter opened.

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Did the Century CS-55 movements get adapted for use in the Century JJ 35/70? Over on r.a.m.t, they are looking for evidence that 55 mm prints of "Carousel" and "The King and I" were actually used in theatres. Where were the projectors installed? Were they 6-perf or 8-perf pulldown? In any case, with a high speed movement, the stress on the perfs had to be pretty high, especially with triacetate prints.

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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

Rory

I'm not surprised at the quality you are getting with a 3-blade shutter. Certainly gets rid of flicker, and allows a high level of illumination. As you note, the lower efficiency of a 3-blade shutter needs a larger lamp for a given image size.

What size and type of screen are you lighting with that 4500 watt lamp? What is the screen luminance? With a curved gain screen and decent optics, I would guess a screen up to about 20 x 48 feet would be possible, even with a 3-blade shutter.