Film-Tech Forum ARCHIVE: conical shutters

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Posted by Erkan Umut (Member # 330) on 03-06-2006, 06:10 PM:

Are the open sectors and closed sectors (blades) of conical shutters are different in size and shape?
If yes, why?

Posted by Monte L Fullmer (Member # 2797) on 03-07-2006, 12:03 AM:

The Simplex XL/35 machines with the conical shutter were designed to cut the light where the round of the light beam was at its smallest, which was next to the aperture opening-thus allowing the most light out through the lens per rotation.

If one looks at a conical shutter against the monster fan shutters of the earlier Simplexes and Centurys, the blades are cutting the light in the middle of the light stream, thus cutting out quite a bit of light.

There are adjustable shutter blades, which adjustments are made per each blade to make the blades thinner or thicker, are available for the Simplex XL/35 units if more light needs to be available. but shutter ghosting becomes more trickier to remove with thin bladed shutters.

Thus Simplex came out with the Hi-speed Intermittent movement to aid in light output by pulling down the film faster so the non-adjustable shutter can allow more light through per each rotation.

The barrel shutters of the Motiographs and the Ernemanns had the right idea - cutting the light bean on both top and bottom like a gate when the barrel rotated around. But, these units required a mirror that was set back farther than normal so the light angle can go completely through the barrel and not get dispursed around the barrel itself. The old carbon arc lamphouses were good for this since the mirrors had long "f" stops and the angle of light was rather thin heading through the machine.

Posted by John Walsh (Member # 168) on 03-07-2006, 07:40 AM:

I think the reason is; the section that blocks the light during film pull-down must be wider to allow the intermittent enough time. The smaller section only has to block the light.

Posted by John Pytlak (Member # 331) on 03-07-2006, 07:52 AM:

If the shutter blades are not equal in size, flicker will increase significantly. The blade must be large enough to block the light while the film is moving during pulldown, or you will see travel ghosting. The "flicker" blade(s) should be the same size.

Posted by Stephen Furley (Member # 1277) on 03-07-2006, 08:28 AM:

quote: Monte L Fullmer
The barrel shutters of the Motiographs and the Ernemanns had the right idea - cutting the light bean on both top and bottom like a gate when the barrel rotated around.

Some projectors did basically the same thing with two contra-rotating conventional shutters.

Then there have been various designs of shutterless projectors, not including the Philips pulsed lamp ones.

Posted by Dave Macaulay (Member # 813) on 03-07-2006, 09:16 PM:

quote: Monte L Fullmer
The barrel shutters of the Motiographs and the Ernemanns had the right idea - cutting the light bean on both top and bottom like a gate when the barrel rotated around

I always figured this was a way to avoid infringing a patent on the disc shutter. The early history of projector companies seems mostly about patents, people making up nutty ways to accomplish something when the obvious ways were patented. How else can you explain the Simplex shutter compensator?
Barrel shutters seem to work ok, but I've noticed the counter-rotating shutters in the Century CC cause a lozenge-shaped bright area in the image across the screen at the aperture centreline. This is unavoidable because the light is ON at the centreline more time than at the top and bottom. I think the barrel shutters should do the same thing, I have never noticed it though. Possibly the "rearward" blade is at such a different point in the light cone that the effect is reduced to invisibility?

Posted by Monte L Fullmer (Member # 2797) on 03-08-2006, 12:15 AM:

quote: Dave Macaulay
a lozenge-shaped bright area in the image across the screen at the aperture centreline.

... be it the classic "hot spot" due to the bulb focus is too tight and shooting the bare light through an anamorphic lens?

I ran Motiographs for a good dozen years - both with 11mm Ashcraft lamphouses and with the Strong 4k Futura II's. Both lamphouses have the ball of light way back in the lamphouse so that the angle of light is very slim so all of the light indeed goes completely though the barrel shutter at opening and through the aperture. With this proper lamphouse/machine setup, the presentations on the screen are fabulous coming out of a Motiograph.

If the right lamphouse is used, I'd kill any day for a Motiograph booth compared to any Simplex booth any day of the week- for domestic made machines. (Import is the Cine V8r/V18 setup)

Monte

Posted by Steve Guttag (Member # 268) on 03-09-2006, 06:19 AM:

Double shutters will ALWAYS introduce a hotspot...furthermore, any slop in the gear-train is exaggerated and will introduce a hot spot that bounces...often misinterpreted as a flickering lamp. The bounce is always there...it is slow and lumbering if the blades are heavy and the gear train is sloppy, it is more violent if the blades are light and the gear train has minimal slop.