8mm Forum: What 8/S8 proj.'s have/4 bladed shutters?

This is topic What 8/S8 proj.'s have/4 bladed shutters? in forum 8mm equipment for sale/trade at 8mm Forum.

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Posted by Ted Langdell (Member # 479) on November 25, 2005, 03:01 AM:

Am interested in what 8mm or Super 8mm projectors have four bladed shutters.

Any info greatly appreciated.

Thanks,
Ted

Posted by Jan Bister (Member # 332) on November 25, 2005, 06:26 PM:

I've never heard of any like that, nor do I really see the point in a 4-bladed shutter... [Eek!]

Posted by Ted Langdell (Member # 479) on November 26, 2005, 11:35 AM:

With four or more blades, the number of times per second the image from a frame is repeated increases compared to machines with two or three blade shutters.

It reduces flicker on the screen, but also has some benefits for my application.

If a projector is running at 8mm "silent" speed (16fms, nominally) then four blades will get the repetition rate above 1/60th of a second... the point at which I can use the "clearscan" shutter speed feature on my video camera to capture one of the repetitions while recording,

So, I'm looking for projectors with more than three blades.

Know any?

Posted by Jan Bister (Member # 332) on November 26, 2005, 11:47 AM:

Well, Kevin mentioned in response to your other thread that some Elmos may be outfitted with 5-blade shutters.
These would give you 90Hz light-dark cycles at 18fps, or 120Hz at 24fps - both suitable for telecine with an NTSC (30fps interlaced, or 60Hz) camera.
I just don't think 4-blade shutters exist because these would give you 72Hz and 96Hz, respectively - pretty useless frequencies for either NTSC or PAL video capture. So what you're looking for is 5-blade shutters...

Posted by Ted Langdell (Member # 479) on November 26, 2005, 12:30 PM:

Hi, Jan...

Video cameras with a "clearscan" feature were initially designed for shooting computer CRT's with non-NTSC refresh rates. As you know, refresh rates are all over the map, including some of the rates you mentioned.

I've had good success using a three-blade machine at 24fps (nominally a 72nd of a second) and tuning the shutter above and below that "refresh" rate to eliminate flicker as viewed on an NTSC monotir and "white bounce" as viewed on a waveform monitor.

This method of transferring sound-speed films worked much cleaner than using the true 24p feature of the camera involved... and we tried both the 24p and 24p advanced settings.

As you can figure out... 24p video is not gonna work on silent films with a nominal speed of 16 or 18fps.

Hence the need for four or more blades in order to keep the projected speed near the nominal shooting speed for natural motion and ease of transfer.

I gather that a Bolex 18-5L might work for Super 8 silent since it has five or six blades in use during 18fps projection.

What other machines come from the factory with more than three blades?

Who makes retrofit shutter discs with more than four blades for 8mm and Super 8mm projectors?

Ted

Posted by Jan Bister (Member # 332) on November 26, 2005, 02:43 PM:

I honestly have no idea. With the right tools and some ability, you could conceivably make your own shutter for the particular projector you're using. Many use a simple disc-with-blades (sort of like a propeller), others like the Elmo ST-1200 use a shutter wheel, where the wheel itself runs around the outer edges of the blades. In either case you might be able to cut out the existing blades and fashion your own, then somehow put these on...

Perhaps trying another video camera would be the easier way. [Wink]

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