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Topic: 3-bladed shutters

Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 01-11-2004 08:03 PM

Actually lets do a little experiment
the smaller window of light gives less time for the eye to intigrate the volume of light (lux/time) as compared to the 2 blade that in effect has a greater amount of light over time
So as such there is less difference occuring for the brain to intigrate
Many years ago Imax did a lot of research into the whole issue of intigration of light over area and time and that was part of the determination re there screen brightness levels

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 01-11-2004 08:33 PM

Glad to be involved in another debate.

I'm glad others have seen the apparent increase in grain. What is the visual version of phycho-acoustic?

The other thing I forgot to mention is there is also an apparent loss of contrast ratio.

This is all anecdotal as I did the conversion on Dolby's DP75's in SF and used a reel of Mad Max which I knew by heart as a reference. The difference was immediate.

I went back of course and rechecked the light with a Minolta.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 01-11-2004 08:37 PM

None of this is exactly selling me on the idea of 3X. [Cool]

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Warren Smyth
Expert Film Handler

Posts: 158
From: Auckland ,New Zealand
Registered: Aug 2003

posted 01-11-2004 08:45 PM

If there is an apparent increase in the perception of grain due to a reduction in the apparent flicker, it would indicate there is an apparent increase also of the overall resolution of the image. Has this been the experience of those of you who are in the position to compare 2 blades with 3?

If not, here is another theory as to the possible cause of the phenomenon which could easily be tested. Is it possible that those situations where 3 blades are being used, tend to have, due to smaller screens and less chance of flashing on highlights, the tendency to have higher illumination? A brighter picture maybe pushing up the greys and blacks enabling this density of emulsion to be observed better by the viewer. In short, perhaps the apparent grain is more a function of brightness than the apparent reduction of flicker.

It's interesting how, in order to improve the technical quality, there is so often a trade off.

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Matt Zeiner
Expert Film Handler

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

posted 01-11-2004 09:44 PM

this is getting interesting...I might install a 2-blade shutter in one of my machines at the next screening. Match the brightness and see. There are some things that I really like about the image out the 3X and some that I really don't. Come to think of it, Sam, I am pretty sure that I have always been displeased with the overall contrast onscreen. Everything is a trade-off.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 01-11-2004 10:00 PM

An increase in perceptible resolution ought to be demonstrable with appropriate test films.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 01-11-2004 10:23 PM

I agree. Since the grain is what actually forms the image, if you see the grain more clearly, you also are seeing the image more clearly, i.e., it is sharper. I've always preferred the "look" of a three-blade shutter on a smaller screen, if only for the greatly reduced flicker perception.

I've never heard of a shutter having an effect on tone scale (contrast) if all else is equal (lens, port glass, luminance).

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 01-11-2004 10:30 PM

Contrast is not something that should be a side effect of a three bladed shutter. Overall contrast is more reliant on the optics and screen surface being used.

As for perceived sharpness I would suspect that the frame being projected is exposed to less heat and is popping out far less with the smaller shutter openings. This would allow the film to stay more in the shallow depth of focus that most lenses are capable of. Interestingly, myself and several others here have also noticed a sharper perceived image when using a high speed intermittent, but in this case with even wider drive inn openings.

In a pinch and to cut light level to permissable levels I have also used a two blade shutter with very narrow openings, in fact two two balded shutters on top of each other. A similar effect was also noted with more perceived sharpness in the image. This was one reason I speculated about there being less heat on the frame. In the 40's Kodak did some interesting 16mm high speed filming of actual 35mm frames popping when the light hit them. They also came up with a way to measure it using a Simplex -7.

Matt, A good visual test might be to use the Schnelder resolution film which is mainly black, absorbs more heat, and pops more when its in the framem. The differences in sharpness should be obvious between a 2 and a 3 blade shutter when running at the same light levels on screen.

Mark @ CLACO

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 01-11-2004 10:41 PM

quote:
In the 40's Kodak did some interesting 16mm high speed filming of actual 35mm frames popping when the light hit them. They also came up with a way to measure it using a Simplex E-7.

Yup! That work was done by Kodak's Dr. Fred Kolb, and led to several important SMPTE papers. It also helped lead to curved gates and better heat filters to improve focus and stability. Paul Preo was another Kodak researcher who worked with Dr. Kolb.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 01-11-2004 10:43 PM

John,
That would be a good group of papers to post in the manuals section if you could get ahold of them!!!
Mark

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 01-11-2004 11:08 PM

I'll see if I can get permission for reprinting from the SMPTE (the copyright holder). jhawk got permission for Preo's winding orientation paper and my paper on the SMPTE Theatre Quality Evaluation Program, so it's likely they will let them be republished here.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 01-11-2004 11:31 PM

I have a water circulator running on my JJs with 2K lamps (Super Lume X). It is pretty obvious (at least to me) when the circulator is not on. The focus is substantially sharper when the circulator is running, and yes that's even with 2000 watt lamps.

I've been toying with the idea of 3 bladed shutters. If the contrast is lowered at all though, there is no way will I pursue it. I don't really see how that could be, assuming the light levels are matched.

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Marc Jones
Film Handler

Posts: 82
From: Elizabethtown, KY
Registered: Jun 99

posted 01-11-2004 11:35 PM

I don't know if this would apply, but at one time I was told that if you used a three blade shutter then you would get less flicker in the film if you recorded it with video recorder?.

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Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000

posted 01-12-2004 01:54 AM

Not sure how that would affect videoing it in NTSC, but with PAL a two-blade shutter (in mechanical telecines) with the film running at 25fps is the norm - each frame scanned twice fits precisely into the 50hz scanning rate. Some machines I've seen also have a 16 2/3fps option, scanning each frame three times.

quote:
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.

It was the time factor I'm thinking of. With a two-blade shutter the 'attack' and 'decay' phases take longer than with three blade (which is fitting an extra cycle into the same length of time), therefore the level of illumination at any given point on the screen across the entire cycle will appear to the naked eye to fluctuate less. In other (very crude) words, because you're seeing less of a flicker, you're able to see more detail in the projected image.

Agreed, though, that heat on the film is another factor.

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Carl Martin
Phenomenal Film Handler

Posts: 1424
From: Oakland, CA, USA
Registered: Feb 2002

posted 01-12-2004 02:39 AM

i would think the "attack" and "decay" would take just as long regardless of 2 or 3 blades. assuming the blades are the same and spinning at the same rate.

or are the 2 "non-essential" blades smaller than the one that obscures the film travel? my interpretation of sam's statement that:

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

is that a 3-bladed shutter has blades the same area as a 2-bladed shutter, blocking ~75% rather than ~50% of the lamphouse's output.

so you'd need twice as much light. is that right?

what about 5-bladed shutters? how do they let any light through at all? does one need a special fast intermittent?

carl

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