Film-Tech Forum ARCHIVE: 2 blade and 3 blade shutter difference

This is topic 2 blade and 3 blade shutter difference in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Iben Jimenez (Member # 3713) on 04-21-2006, 06:35 PM:

What is the difference between 2 blade and 3 blade shutters? What does 48 and 72 interruptions of light per second mean?

Posted by Kenneth Wuepper (Member # 1174) on 04-21-2006, 08:38 PM:

Iben,

The shutter is needed to block the light while the film is moving from one frame to the next in front of the lens or else you would see a smearing caused by the film traveling in front of the lens. Although a shutter of one blade could accomplish this, it would be mechanically out of balance and, because the human eye can see slow flashes of light, would cause a flicker to be seen by the viewer.

Additional blades on the shutter will cause the light to be blocked during film movement and also provide additional flashes of light to eliminate the filcker as seen by the viewer.

For discussion only, let's make some symbols:
The shutter blocks the light -
The shutter blocks light and film moves =
The shutter is out of the light path and a flash is shown 0

Therefore the action of the projector and shutter with one blade would look like this:
=0=0=0=0=0=0=0=0=0= 24 movements per second 24 flashes 1 blade
=0-0=0-0=0-0=0-0= 24 movements per second 48 flashes 2 blades
=0-0-0=0-0-0=0-0-0= 24 movements per second 72 flashes 3 blades

Hope this helps.
KEN

Posted by David Stambaugh (Member # 1102) on 04-21-2006, 09:03 PM:

Good explanation Ken. [Smile]

Posted by Eric Robinson (Member # 2966) on 04-22-2006, 12:03 AM:

Yes Ken great insight. I was wondering the other day how our two blade shutter could be eliminated and a new design could introduce light blocking only during frame advance, but I was unaware of the human ability to percieve a flicker from this design. Now I must ponder some more...

Posted by Monte L Fullmer (Member # 2797) on 04-22-2006, 01:58 AM:

..plus the 16fps for silent films also used the 3 blade shutter to also get the 48 interruptions per second.

Posted by Louis Bornwasser (Member # 3063) on 04-22-2006, 07:55 AM:

Eric; a one blade at 2x speed would still be 48 blinks-per-second but would have the advantage of reducing the open/close time. (Christie & Kinotone) Louis

Posted by Gordon McLeod (Member # 33) on 04-22-2006, 11:38 AM:

and the GK21 had a single blade high speed shutter on some as well

Posted by Thomas King (Member # 2745) on 04-22-2006, 04:48 PM:

On a related note: does anyone use a 3-blade shutter at 24fps? I tried it once, but found that increased flicker rate wasn't worth the drop in light output.

Posted by Steve Guttag (Member # 268) on 04-22-2006, 07:00 PM:

MANY screening rooms run 3-wing shutters at 24fps.

Posted by Mark Gulbrandsen (Member # 72) on 04-22-2006, 07:50 PM:

quote: Thomas King
On a related note: does anyone use a 3-blade shutter at 24fps? I tried it once, but found that increased flicker rate wasn't worth the drop in light output.

The real idea being to bump the light up the same percentage that the 3-blade shutter decreases it for any given format. 3- bladers are a definate improvement and allow higher light levels if one needs or wants it.

Mark

Posted by Eric Robinson (Member # 2966) on 04-22-2006, 11:36 PM:

Most of the projectors I maintain are Simplex 35. As far as I know there are no options for changing the shutter speed. Although I have heard that there was a shutter blade in the past with wider blades.

Are there options for Simplex 35's? ie like for a Melinium?

Posted by Monte L Fullmer (Member # 2797) on 04-23-2006, 02:09 AM:

quote:
Although I have heard that there was a shutter blade in the past with wider blades.

Are there options for Simplex 35's? ie like for a Millenium?

..and cut out more light with a wider blade?

Options are for the Simplex35 units in as well as the Mil2k's is the usage of a shutter with adjustable blades that increases the light output by reducing the interruption attack slightly-mainly for usage in drive-ins and large screen presentation venues..along with the high-speed intermittent assembly to really make this the most light efficent presentation from a Simplex.

-Monte

Posted by Mark Gulbrandsen (Member # 72) on 04-23-2006, 06:58 AM:

Monte,

The adjusta blade shutter is no longer available from Strong.

Mark

Posted by Eric Robinson (Member # 2966) on 04-23-2006, 12:28 PM:

As I understood it, the current production Simplex shutter blade has been trimmed down to the smallest size possible.

I know that even when I have the shutter timing set perfectly, I can still detect slight ghosting at the extreme top and bottom edges of the screen.

It would seem that the ghosting would increase if the shutter blades were any smaller. Unless I guess if you used the high speed intermittent.

I'm guessing these intermittents simply have a faster frame adavnce cycle?

Are they more expensive?

More prone to break?

Do they fit all Simplex 35 XL's?

Posted by Steve Guttag (Member # 268) on 04-23-2006, 05:27 PM:

3-wing shutters are available for Simplexes and are standard on the PR1020, PR1030 projectors. Strong did loose the adjusta-shutters as Mark mentioned.

Simplex, long ago, standardized on the 84-degree shutter though. If everything is working perfectly in your machine with near zero gear lash, the 84-degree shutter should work. The problem is if Strong cuts the shutter even slightly less or if you have too much slop anywhere in the drive train...you WILL get a very faint ghost. Century needs 90-degree shutters, period (on 35mm). Century tried wider opening but they ALWAYS have ghosting then.