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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » 3-bladed shutters (Page 1)

 
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Author Topic: 3-bladed shutters
Matt Zeiner
Expert Film Handler

Posts: 146
From: Windsor, CT USA
Registered: Sep 2003


 - posted 01-10-2004 11:05 AM      Profile for Matt Zeiner   Email Matt Zeiner   Send New Private Message       Edit/Delete Post 
I have 2 old (black cast) XLs that have 3 bladed shutters in a screening room I service. There is plenty of light on screen. Wondering if there is any tangible benfit to using them as opposed to the standard 90 degree bowtie...these are some of the nicest running machines I have ever come across, btw. Incidentally, there are no heat sheilds installed on either machine.

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Sam D. Chavez
Film God

Posts: 2053
From: Martinez, CA USA
Registered: Aug 2003


 - posted 01-10-2004 11:46 AM      Profile for Sam D. Chavez   Author's Homepage     Send New Private Message       Edit/Delete Post 
The benefit is the flicker rate goes from 48 to 72 so the image is smoother.

You lose 50% more light, relative to a two bladed shutter, not 33% as one would initially suppose.

Interestingly, the grain in the image becomes more pronounced with a three bladed shutter. There are varying opinions as to why. One possibility is that the film breathes less (shorter pulses of light) so you are getting a more accurate view at what is actually on the frame. Perhaps it is more complicated and has something to do with the persistence of vision phenomenon.

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John Pytlak
Film God

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


 - posted 01-10-2004 12:13 PM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
I never heard that the shutter had any effect on perception of grain. Simplex's Willy Borberg and Kodak's Dr. Fred Kolb did quite a bit of reseach about the effects of radiant energy on the film frame back about 50 years ago. Borberg found that for very high levels of radiant energy, a two-blade shutter was preferred because the film frame had a longer time to achieve a stable position, especially during the second exposure:

"Effect of Gate and Shutter Characteristics on Screen Image Quality", Willy Borberg, SMPTE Journal, October 1957, Volume 66, pages 623-627

Dr. Fred Kolb published several SMPTE papers during the late 1940's and the 1950's, including the use of air pressure to cool and stabilize the film frame, and the use of wet gate projection. Dr. Kolb is still active in retirement, and was one of my mentors at Kodak.

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Matt Zeiner
Expert Film Handler

Posts: 146
From: Windsor, CT USA
Registered: Sep 2003


 - posted 01-10-2004 12:16 PM      Profile for Matt Zeiner   Email Matt Zeiner   Send New Private Message       Edit/Delete Post 
OK - I have noticed an exceptional lack of motion artifacts, come to think of it. Also noticed the grainyness - even on full-frame anamorphic prints (I am also the projectionist there). Thanks.

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John Pytlak
Film God

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From: Rochester, NY 14650-1922
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 - posted 01-10-2004 12:26 PM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
The relatively small screens used in most screening rooms don't require much radiant energy. So a three-blade shutter is almost always an advantage for a smaller screen, greatly reducing the visibility of any shutter flicker. It also is useful if you need to run the projector at less than 24 fps, showing silent films for instance, or allowing the lab color timer more time to judge the scene-to-scene color balance.

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Warren Smyth
Expert Film Handler

Posts: 157
From: Auckland ,New Zealand
Registered: Aug 2003


 - posted 01-10-2004 04:37 PM      Profile for Warren Smyth   Email Warren Smyth   Send New Private Message       Edit/Delete Post 
I'm pleased the subject of these shutters have come up. I have considered doing a conversion to a 3 bladed shutters in a home theatrette on Kalee 19s. A loss of light output is no problem as arcs are used on a matt non perforated screen that is only 12 feet wide on scope. The carbons are currently under run, so a less efficient optical train would be an advantage. I could then raise the current to give higher arc stability. (The 6mm neg and 7mm pos don't burn perfectly at 38 amps). I can't raise the level at the moment because the light output would be too high. The highlights are on the point of flashing now. Besides the fact that the cut off periods must equal the exposed periods, are there any other reguirements with regards making the shutter?

I have never heard of the apparent grain problem however, which is a real concern and making me have second thoughts. Any suggestions for and against are very welcome.

I have also considered irising down the lens if there is still plenty of light, as I understand focus may be improved. The wide screen lens is two and a half inch and the image appears sharp over the full width, even with an angled light beam. What is the current thinking on irising down? Are there any disadvantages?

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Stan Gunn
Expert Film Handler

Posts: 176
From: Clematis, in the hills near Melbourne Australia
Registered: Aug 2000


 - posted 01-11-2004 12:31 AM      Profile for Stan Gunn   Author's Homepage   Email Stan Gunn   Send New Private Message       Edit/Delete Post 
Hi Warren

My feeling is it would be the way to go as it would decrease light output and improve focus, [thumbsup] the mirror can also be defocused a tad and should have no effect on focus or light colour.

I make an asumption you are useing a President lamp house [Big Grin] ,another way would be to fit a smaller mirror or mask off the mirror.

Kalees optical system was certainly very good when useing the full Kalee system, also the Kalee lamp houses were made to run a trim of 5mm and 6mm rods another way you may be able to take.

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Warren Smyth
Expert Film Handler

Posts: 157
From: Auckland ,New Zealand
Registered: Aug 2003


 - posted 01-11-2004 04:58 AM      Profile for Warren Smyth   Email Warren Smyth   Send New Private Message       Edit/Delete Post 
Stan,
You are right. It's a complete Kalee plant - Presidents, 543 sound heads and even 6 channel G.K.Duosonic rack and panel valve power amps, ones I once ran for 70mm. They keep me warm in the winter (48 valves).

I agree the light output is pretty good from Kalee equipment, even though the 19s (and 20s)have the two bladed shutter, unlike their mate the 21 which had the single fast blade. I think the 21s were sometimes used in drive-ins in Aust because of their light efficiency.

I have tried 5mm and 6mm trims but the smaller crater size does compromise coverage for 35mm. I think these were used mainly for 16mm. They worked well with 16mm Bell and Howell projectors and Kalee Universal arcs but I'm not really happy with the results for 35mm with a slight hot spot. Mind you, that's a common occurance in plexes with xenons and high gain screens. No one seems to worry, but I'm a little traditional.

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Leo Enticknap
Film God

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From: Loma Linda, CA
Registered: Jul 2000


 - posted 01-11-2004 05:29 AM      Profile for Leo Enticknap   Author's Homepage   Email Leo Enticknap   Send New Private Message       Edit/Delete Post 
The only reason I can think of for using three-bladed shutters now is for showing silent films which run at speeds significantly below 24fps. Most designs of 'bow tie' blade will block the light source for long enough at low speeds for the human eye to pick it up, resulting in a visible flicker on the screen. In extreme cases (e.g. a Vic 5 two-blade shutter running at 16fps) the flicker is so pronounced that I guess there could be a health and safety issue with epileptics and strobe effects.

The smaller blades of a three-bladed shutter will allow you to go right down to 16 without any visible flicker. As Sam points out the quid pro quo is, of course, greater light absorption, meaning you need a more powerful xenon. If I were setting up a projector to show 24fps most of the time but with the facility for occasional, regular silent screenings (which would be the case with most arthouse venues) I would go for a design of projector in which changing the shutter is a reasonably simple operation and a slightly overpowered xenon. The machine would run with a two-bladed shutter and low amps for 24, and with the three-blade fitted and the current wound up a bit for the silent shows.

If silent shows are being done very regularly or you are dealing with pre-installed projectors which make shutter changing very difficult, it might be worth going for permanently installed three-blades and living with the extra electricity and lamp costs.

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John Pytlak
Film God

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From: Rochester, NY 14650-1922
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 - posted 01-11-2004 07:39 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
For a 12-foot wide screen in a small screening room, three-blade shutters would be fine. Even at 24fps, some people are sensitive to 48 Hz shutter flicker in brighter scenes, and going to 72 Hz greatly reduces the flicker perception.

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Bruce McGee
Phenomenal Film Handler

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From: Asheville, NC USA... Nowhere in Particular.
Registered: Aug 1999


 - posted 01-11-2004 09:08 AM      Profile for Bruce McGee   Email Bruce McGee   Send New Private Message       Edit/Delete Post 
I've got several Kodak Pageant 16mm machines that have the 'Super 40' shutter. At silent speed, the shutter is a 3 blade. At sound, it's a 2 blade. This makes the silents that I run look really nice. I also like the way sound film looks when I get a shutter that is stuck in the 3 blade mode. Sure, there is a bit of light-loss, but in a small room it is OK, at least for me.

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Matt Zeiner
Expert Film Handler

Posts: 146
From: Windsor, CT USA
Registered: Sep 2003


 - posted 01-11-2004 01:10 PM      Profile for Matt Zeiner   Email Matt Zeiner   Send New Private Message       Edit/Delete Post 
I'm running mine on a 24' screen, pair of super lumex 2k lamps. Even with the 3 blade shutter I have tons of light. The picture is always beautiful, though especially on blowups the grain is more apparent than on 2-blade systems I have run. Anybody care to speculate as to why?

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Leo Enticknap
Film God

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From: Loma Linda, CA
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 - posted 01-11-2004 02:32 PM      Profile for Leo Enticknap   Author's Homepage   Email Leo Enticknap   Send New Private Message       Edit/Delete Post 
OK, here's a complete and utter speculation. With a relatively overpowered lamp and a three blade shutter the intensity of illumination is more constant. Therefore you will see less of the 'attack' and decay' as the shutter blade covers and retracts from the light source than you would with a two-blade shutter. Because the light intensity is more static, you're looking more closely at detail in the picture - therefore seeing the grain - than you would do both with a lower overall light level (i.e. less footlamberts) and a more pronounced up and down cycle.

This is all I can think of...

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Matt Zeiner
Expert Film Handler

Posts: 146
From: Windsor, CT USA
Registered: Sep 2003


 - posted 01-11-2004 03:37 PM      Profile for Matt Zeiner   Email Matt Zeiner   Send New Private Message       Edit/Delete Post 
Since we're speculating, here's mine: Maybe since we are not as distracted by the flickering at 48hz (especially in shots that utilize camera movement) and since there is less shutter "smear," the film grain is more clearly resolved on screen??

- I guess that's pretty much what Leo said...

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Steve Kraus
Film God

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From: Chicago, IL, USA
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 - posted 01-11-2004 07:53 PM      Profile for Steve Kraus     Send New Private Message       Edit/Delete Post 
Illumination more constant? How so? It still goes from zero to maximum, holds there, then drops to zero and holds, with rise and fall times dictated by the nature of the shutter (diameter, placement in the light beam, 3 blade or 1 blade running 3X etc.) If you mean more even across the frame that doesn't follow from 3X shutters either. If you have 2X and go to 3X you must raise illumination but not necessarily evenness. You could raise it even more and make the light more even but you could have done that without 3X shuttering with even less light.

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