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Topic: Viewing Angle

Lyle Romer
Phenomenal Film Handler

Posts: 1400
From: Davie, FL, USA
Registered: May 2002

posted 03-09-2006 02:00 PM

I was reading through the TAP manual in the archive and was hoping somebody could explain a couple of the points about viewing angle.

quote:
The horizontal viewing angle (field of vision) from the most distant seat should be no less than 26 degrees (36 degrees recommended).

What is this angle? From the seat to the center of screen? From seat to edge of screen?

quote:
The vertical viewing angle from the first row should not exceed 35 degrees.

Is this 35 degrees from head to bottom of screen? Head to top of screen? Floor to bottom of screen? Floor to top of screen?

quote:
To keep the viewing angle distortion at a minimum, all seats should be contained within a 45 degree Iso-Deformation line, as defined in EG18-1994.

Does this just mean to draw a line from the center of the screen to the back wall and then draw a 45 degree line on each side and make sure all the seats are in there?

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Brian Guckian
Jedi Master Film Handler

Posts: 594
From: Dublin, Ireland
Registered: Apr 2003

posted 03-09-2006 06:19 PM

The Horizontal viewing angle is that angle between two lines drawn from the eye position of a viewer in the centre of the farthest row to each edge of the screen on 'Scope. (NB - use of common height for all ratios is assumed!).

If this angle is less than 26 degrees, the image will seem too small for viewers at the back of the theatre, and likewise, much greater than 36 degrees will overwhelm viewers near the front.

The Vertical viewing angle is that angle between two lines drawn from the eye position of a viewer in the centre of the front row*; the first line being from the eye position to the top of the screen (again - common height is assumed), the second a horizontal line from the eye position to the screen.

If this angle is greater than 35 degrees viewer comfort is seriously compromised; conversely a low vertical viewing angle could mean the Bottom Picture Line (BPL) is too low down, compromising sightlines.

On architectural plans, the Horizontal angle is obviously examined by looking at the Auditorium Plan, whilst the Vertical is done by looking at the Section.

Also - references to the edge of the screen and top of the screen here mean the edges and top of the image, not the masking / screen frame, etc.

Now the 45-degree Iso-Deformation line as outlined in SMPTE EG18-1994 is a much more complex matter and one needs to refer to that document, or others. I believe EG18 was archived by the SMPTE some time ago, and it needed revision to take account of changes in cinema design practice since the time of its publication. Hopefully John Pytlak could help more on this.

Hope that helps!

* If the rows are curved or banked, one should use the closest seat to the screen as the reference position

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-09-2006 07:07 PM

EG18 was a document that was too good, and that was its only "fault"...it was shelved for political reasons only for nothing in it was "out of date."

Anyway...to the 45-degree issue. Once one has a 45-degree or greater angle of view to an image on screen, it has been shown that it is objectionably distorted. Thus one's viewing angle to any part of the screen from any seat should be 45-degrees or less.

The 26-degree angle from the last row, center seat to the edges of the screen was primarily to keep the stereo sound "image" effective...with a long, skinny theatre having very poor stereo perception.

The 35-degree angle refers to the comfort level of a person's head articulation. The document showed the comfortable range of motion in the human head, the normal viewing angles and such.

Sorry, the but the withdrawing of EG18 is a sore spot for me and the manner in which it was withdrawn quite embarrassing. Beyond that, I can't discuss.

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John Pytlak
Film God

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

posted 03-10-2006 09:58 AM

EG18 had the risk of drawing an engineering organization into lawsuits over the misinterpretation of good engineering design with customer use specifications.

Just go to the source, which is excellent:

"Design of Large-Screen Motion Picture Theatres", Will Szabo, SMPTE Journal, Volume 85, March 1976

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Dick Vaughan
Phenomenal Film Handler

Posts: 1032
From: Bradford, West Yorkshire, UK
Registered: Jul 2000

posted 03-10-2006 11:29 AM

quote: Steve Guttag
The 35-degree angle refers to the comfort level of a person's head articulation. The document showed the comfortable range of motion in the human head, the normal viewing angles and such.

In the UK the 35 degree angle actually formed part of the requirements for issuing a cinema licence. We had to get special dispensation as a "special venue" when we opened the first IMAX theatre in the UK as we obviously couldn't comply.

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Gordon McLeod
Film God

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

posted 03-10-2006 01:12 PM

EG18 should not have been withdrawn it still represents the purpose of the society to draw and set standards for presentations whether a theatre chooses to ignore it is at its own peril

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Lyle Romer
Phenomenal Film Handler

Posts: 1400
From: Davie, FL, USA
Registered: May 2002

posted 03-10-2006 08:29 PM

What was so controversial in EG18 that it had to be put out to pasture?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-10-2006 09:29 PM

It told you how to build your theatres correctly. Now that is a controversy!

The problem stemmed from a "Guideline" (SMPTE's lowest form of document) being used as some form of "Standard" and/or being incorporated into law.

Somehow the industry is better served to not have a document to tell architects/exhibitors how to properly design theatres. Everything in that document was derived from actual practice and experimentation rather than just some theory.

Imagine, if you will, a document that defined such parameters as sightlines, areas of comfort for human head movement and visibility as well as taking into account geometric distortions from extreme viewing angles. With all this information now imagine a cone of acceptance that virtually defines the proper areas to place seats for optimal movie viewing...now imagine if some people don't find themselves within that cone.

Better to get rid of a document like that than to actually build your theatres properly.

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Lyle Romer
Phenomenal Film Handler

Posts: 1400
From: Davie, FL, USA
Registered: May 2002

posted 03-10-2006 09:35 PM

I guess we can blame it on the lawyers. My opinion is that a movie theatre should be the optimum venue to view a movie and therefore all seats should be located where the patron will have a proper view.

Is there any way to find out what all these guidlines were?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-10-2006 09:43 PM

Whereas the document was "Withdrawn" I don't know if it has any availability (John P would know). If it had been merely archived, then it would definatley be available from the SMPTE.

There are copies of it out there though...it is a copyrighted document so it is not a simple matter to just post it. With the right SMPTE CDs, there is an electronic version of it (I want to say it was a mid 1990s version).

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Lyle Romer
Phenomenal Film Handler

Posts: 1400
From: Davie, FL, USA
Registered: May 2002

posted 03-10-2006 10:04 PM

Are there still people around that know all the angles to calculate the "cone of acceptance"? Is it just the angles that I posted in the original post?

Is there an angle used to calculate the highest seat in a stadium configuration?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-10-2006 10:08 PM

It matters not stadium seating or slope floor...that is a misconception on most people...

It is best done with CAD nowadays though pencil and paper may be used for sure.

You note where the bottom of your image is, and draw sight lines such that people can see over the tops of the heads of the people in front of them...ACAD makes it easy...most people that do this have their "dude" that defines the person's eye height and head top to place in the seats.

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Lyle Romer
Phenomenal Film Handler

Posts: 1400
From: Davie, FL, USA
Registered: May 2002

posted 03-12-2006 09:54 PM

quote: Steve Guttag
Anyway...to the 45-degree issue. Once one has a 45-degree or greater angle of view to an image on screen, it has been shown that it is objectionably distorted. Thus one's viewing angle to any part of the screen from any seat should be 45-degrees or less.

Just to clarify this point, this means that if you take a seat, draw a straight line to the screen and then draw a line to either screen edge, the angle should not exceed 45 degrees, correct? I am differentiating this from drawing a line to both screen edges and having that angle be less than 45 degreens.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-13-2006 07:45 AM

Your description is correct for a flat screen, for a curved screen you need to worry about 45-degrees off the tangent of the curve...but often the critical one on that is to the vertical. The person in the front row will have a very distorted view of the top of the screen.

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John Pytlak
Film God

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

posted 03-13-2006 09:15 AM

quote: Steve Guttag
Whereas the document was "Withdrawn" I don't know if it has any availability (John P would know). If it had been merely archived, then it would definatley be available from the SMPTE.

There are copies of it out there though...it is a copyrighted document so it is not a simple matter to just post it. With the right SMPTE CDs, there is an electronic version of it (I want to say it was a mid 1990s version).

As I said before, go to the source:

quote: John Pytlak
Just go to the source, which is excellent:

"Design of Large-Screen Motion Picture Theatres", Will Szabo, SMPTE Journal, Volume 85, March 1976

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