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IMAX and 35mm Anamophic


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#1 Mathew Collins

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Posted 23 October 2016 - 09:29 PM

Hi,

 

I was reading this link.

 

https://britishcinem...k-knight-rises/

 

A question about the aspect ratio given in the link.

 

"Pfister and Nolan decided to produce dialogue scenes in 35mm anamorphic format and everything else in IMAX format. To put that into perspective, an IMAX 4:3 frame is 65mm wide and 15 perforations long. The image area is approximately 10 times larger than a 35mm frame composed in anamorphic format."

 

My understanding about the picture area of IMAX is 70.41mmx56.62mm and cinemascope is 24.9mm x 11.1mm.

 

Could some explain,

 

1.IMAX 4:3 frame is 65mm wide

2. The image area is approximately 10 times larger than a 35mm frame composed in anamorphic format.

 

-Mathew


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#2 Tyler Purcell

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Posted 23 October 2016 - 09:33 PM

IMAX runs horizontal through the camera and projector, so the sprockets are on the top and bottom. That's generally people's confusion about the format compared to ALL THE OTHER formats, which -outside of vistavision- run vertical.

A standard 4 perf (cinemascope) print is around 5 megapixel. Where an IMAX 15/70 print is 56 megapixel.
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#3 David Mullen ASC

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Posted 23 October 2016 - 10:51 PM

15-perf 65mm negative is about 4:3 but the projection aperture is 70mm x 48.5mm, which is 1.44 : 1.

4-perf 35mm anamorphic projection area is 21mm x 17.5mm, which is 1.20 : 1 but once doubled in width to get rid of the squeeze, it becomes 2.40 : 1.

70mm x 48.5mm is 3395 sq./mm

21mm x 17.5mm is 367.5 sq./mm

Which works out to be a 9.2X difference in area.
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#4 David Mullen ASC

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Posted 23 October 2016 - 11:01 PM

I'm not sure where the 24.9mm x 11.1mm figure comes from -- that's a 2.24 : 1 aspect ratio without anamorphic lenses. The closest thing I can think of is the 2.40 extraction area from Super-35 spherical, which is a crop to 24mm x 10mm. Maybe it's some sort of scanning area spec though usually you'd scan the whole 4-perf 35mm full aperture frame for Super-35.
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#5 Mathew Collins

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Posted 24 October 2016 - 12:01 PM

15-perf 65mm negative is about 4:3 but the projection aperture is 70mm x 48.5mm, which is 1.44 : 1.

4-perf 35mm anamorphic projection area is 21mm x 17.5mm, which is 1.20 : 1 but once doubled in width to get rid of the squeeze, it becomes 2.40 : 1.

70mm x 48.5mm is 3395 sq./mm

21mm x 17.5mm is 367.5 sq./mm

Which works out to be a 9.2X difference in area.

 

 

What is the aspect ratio of IMAX? Is it 1.90:1 or 1.44 : 1?

 

I have red in a document that Roger Deakins framed Skyfall IMAX version in 1.90:1.

 

If we consider physical dimension mentioned in the the right side picture(2.35:1), anamorphic squeeze is 21.95mm x 18.59mm(.864'' x 0.732'').

 

The measurement given by you is 21mm x 17.5mm (4-perf 35mm anamorphic projection area is 21mm x 17.5mm).

 

Is that difference is the difference of 2.35:1 to 2.40:1?

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Edited by Mathew Collins, 24 October 2016 - 12:02 PM.

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#6 David Mullen ASC

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Posted 24 October 2016 - 12:11 PM

Traditional 15-perf 70mm IMAX film print projection is 1.44 : 1. Digital IMAX 4K projection uses a 1.90 : 1 container as its biggest area,
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#7 David Mullen ASC

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Posted 24 October 2016 - 12:19 PM

Camera apertures are usually a bit bigger than projection apertures for formats that are contact printed -- the truth is that most 4-perf 35mm cameras are set-up to expose full aperture (silent era 1.33 : 1) it's that with sound formats like anamorphic, the lens is centered for the sound aperture area rather than the silent / Super aperture area, and the ground glass framelines give you the area to be extracted for the image.

The 4-perf 35mm anamorphic format uses more or less the sound Academy width but the silent / Super height of the negative.

The specific gate size combined with the 2X horizontal expansion determines the aspect ratio.
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#8 David Mullen ASC

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Posted 24 October 2016 - 12:51 PM

Originally the plan for CinemaScope in 1952-53 was to project the 4-perf 35mm silent / full aperture area -- since that is 1.33 : 1, the unsqueezed anamorphic image would become 2.66 : 1, which would have matched the rival Cinerama format that started the widescreen craze in 1952 (Cinerama though was a lot more spectacular than CinemaScope since the image consisted of three 6-perf 35mm frames side-by-side, a total area somewhere between 5-perf 65mm and IMAX).

Multi-channel sound would have been run on a separate 35mm roll of mag stock as Cinerama did.

However before the first CinemaScope movie premiered in 1953 ("The Robe"), a decision was made to put the sound on the 35mm print. 20th Century Fox had Kodak make a print stock with smaller sprocket holes ("CS" perfs) and four thin magnetic stripes were added to the print, two on each side of the image. This shaved the projection aperture width for the image, which was 2.55 : 1 when unsqueezed.

A few years later, Fox decided to print CinemaScope in the same way as normal Academy 1.37 and matted 1.85 movies were printed, with an optical soundtrack on the left side, shifting the projected image over to the right side of the print and reducing the width to 2.35 : 1. I once saw a new contact print struck of an early CinemaScope movie, "20,000 Leagues Under the Sea", and during the credits you could tell that the movie was framed for 2.55 : 1 with the image centered on the print because everything was off-centered slightly when using a modern 35mm anamorphic gate in the projector.

2.35 : 1 was the standard until the early 1970s when the projector gate / mask for anamorphic was slightly reduced in height to hide splices better. The reduced height changed the shape to 2.39. : 1. Then in the early 1980s the overall projection aperture for anamorphic was adjusted again to make a standard width for Academy, 1.85, and anamorphic (.825") but the aspect ratio still came out to be about 2.39.
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#9 Mathew Collins

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Posted 25 October 2016 - 10:42 PM

Thank you David.

 

I have confusion here.

 

Physical dimension(image size) mentioned in the picture (2.35:1), anamorphic squeeze is

21.95mm x 18.59mm (.864'' x 0.732''). This is 1.18:1 by doubling it for anamorphic desqueeze is 2.36:1.

 

The measurement given by you (4-perf 35mm anamorphic projection area) is 21mm x 17.5mm (0.827 x0.689).

I think this is the image size in film for 2.40:1

 

>Then in the early 1980s the overall projection aperture for anamorphic was adjusted again

make a standard width for Academy, 1.85, and anamorphic (.825") but the aspect ratio still came out to be about 2.39.

 

What is 0.825'' measurement for?


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#10 David Mullen ASC

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Posted 25 October 2016 - 11:18 PM

In the early 1980's, the ANSI standard for projection apertures became .825" wide (20.96mm) for scope and 1.85.  Some charts just round 20.96mm to 21mm.

 

.825" was already the standard width for Academy 1.37 and 1.85, 1.66, etc. so it was just the standard for the anamorphic aperture that changed to match the rest.

 

Current standard for an anamorphic aperture for a projector is .825" x .690" (1.1956521 : 1, which doubled becomes 2.3913 : 1.)

 

Now the same chart in the ASC Manual converts that to metric as 20.96mm x 17.53mm.

 

Before the early 1980's, the standard for an anamorphic projector gate was .838" x .700" (1.1971428 : 1, which doubled became 2.3942856 : 1.)  This was the new standard put into place in the early 1970's.

 

In 1957, the standard was set as .839" × .715" (1.1734265 : 1, which doubled became 2.346853 : 1.)  You can see how the height of the gate has been shrinking over the decades to hide any errors in making negative splices.  The space between the frames in CinemaScope was so small that you had to use a special negative splicer to be more precise and any bad splices would show up on screen as a flash of light on the top or bottom of the image depending on the projection. So a thicker frame line due to a shorter gate hid those problems better.

 

Today, for a 2K "scope" DCP, the standard is 2048 × 858 pixels (2.3869463 : 1.)

 

---

 

Now again, I'm talking about projection apertures and aspect ratios.  The camera gate is often larger than the projector aperture -- what matters more is what your groundglass frame lines tell you is the area you are composing within.

 

Panavision, for example, lists in the ASC Manual that their 4-perf 35mm anamorphic camera aperture is .866" x .732" (22mm x 18.59mm) but the truth is that most of their cameras will actually expose Full Aperture, it's just that your lens is centered for the sound aperture and you are composing for the area to be extracted for projection.  But even the standards for the area scanned is slightly different again, which is why sometimes it is simpler to just talk about the area that gets used for projection.

 

What matters the most is that the squeeze/desqueeze is a standard 2X amount. The other difference is mainly in just how much of the negative is trimmed, which affects the final aspect ratio.


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#11 Mathew Collins

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Posted 26 October 2016 - 12:23 AM

Great knowledge. Thank you David.


Edited by Mathew Collins, 26 October 2016 - 12:23 AM.

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#12 Mathew Collins

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Posted 26 October 2016 - 12:48 AM

>but the truth is that most of their cameras will actually expose Full Aperture, it's just that your lens is centered for the sound aperture and you are composing for the area to be extracted for projection.  But even the standards for the area scanned is slightly different again, which is why sometimes it is simpler to just talk about the area that gets used for projection.

 

Is that the reason the physical dimension(image size) mentioned in the picture (2.35:1), anamorphic squeeze is

21.95mm x 18.59mm (.864'' x 0.732'') which different from the 1957's standard 21mm x18mm ( .839" × .715")?

 

21.95mm x 18.59mm (.864'' x 0.732'') is exposed area and 21mm x18mm ( .839" × .715") is anamorphic projector gate.

 

Before scanning does the DI technician select required area from each frame?


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#13 David Mullen ASC

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Posted 26 October 2016 - 01:24 AM

The anamorphic squeeze is 2X.

 

Don't concentrate so much on this drawing's dimensions, it seems to be confusing you, which is why it is better to just think about the area that gets projected.  Besides, it is not an exact science -- there are standards but the actual gates in these cases may or may not be exactly to the standards down to fraction of a millimeter.  And screen masking and focal length of projector lenses can further trim the image.

 

That ".864" width is clearly wider than any of the standards for projection so it must refer to some camera manufacturer's camera aperture for anamorphic.

 

If you look at ARRI's list of camera hard mattes / gates for Arricams and look up the 4-perf 35mm anamorphic one here:

http://www.arrirenta...ormat_guide.pdf

 

You see it listed as "2.35" and the dimensions are 22mm x 18.6mm / .866mm x .732mm, which is actually 2.36559 : 1 once unsqueezed.

 

Generally for a D.I. you'd just scan the whole 4-perf 35mm full aperture area and then crop it for the actual area to be seen in release. Some scanners might be set-up to scan Academy / 1.85 / Anamorphic width instead of Full Aperture (Silent / Super) width.

 

You'd just scan whole rolls, you wouldn't select different areas of different shots, you'd just take the scan into the color-correction session and do any reframing or cropping there.


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#14 Mathew Collins

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Posted 26 October 2016 - 02:08 AM

Thank you David.


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