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Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

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Page 1: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens
Page 2: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Cinema Screen Specification & Design

Andrew Robinson

Managing Director

Harkness Screens

Page 3: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Cinema Screen Specification & Design

• this presentation will focus on importance of the screen in a cinema

• screen often given inadequate consideration at the design stage

• screen can significantly affect the way the film is seen and heard and the overall movie-going experience

• presentation relates to 35mm projection but will also cover digital cinema

Page 4: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Choice of screen impacts on the overall experience:

• picture quality/viewing experience• sound quality/acoustic performance

It can also affect cinema operating costs

Page 5: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen impact on picture quality:

• brightness• colour rendition• contrast• distracting imperfections• overall uniformity of picture

The screen should show the film the way the director intended.

Page 6: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen impact on acoustic performance:

• distortion of sound from behind-screen speakers

• particularly loss of high frequencies

Selecting the right screen can optimise sound quality.

Page 7: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen brightness

International standards exist for brightness levels.

• SMPTE recommendations• 16 ft. lbts (55cd/m2) at centre• 12 ft. lbts at corners• measurements made using white light (no film

running)• the centre of the screen should not be

excessively bright (no hot spotting)

Page 8: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen brightness is affected by many factors

• light emitted from lamp/light source in projector

• light lost between lamp and screen

- mirror

- lens

- port glass

• light reflectance back from screen

The screen is an important factor in the brightness of the image.

Page 9: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Light sources

• modern cinemas have projectors using xenon lamps

• carbon arc technology still used in some older cinemas

• xenon lamps between 2.0 and 7.0 kva are used in modern cinemas

• more powerful lamps cost more, have shorter lives and consume more electricity

Page 10: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Light reflectance

• screen is major factor in amount of light reflected back to audience

• matt white screens scatter light

• 'gain' screens reflect more light back to audience

Page 11: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Light reflectance

Gain screens reflect more light back to the audience

Gain Screen Matt White Screen

Page 12: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Measurement of gain

Projector

Light meter

Magnesium carbonate block

Screen surface

Gain is measured according to British Standard BS 5382

Page 13: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Measurement of viewing angle

Gain is measured at intervals of 10° by comparison with reference standard

Page 14: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Types of cinema screen

Screens are available with various gain levels:• matt white: 'gain' typically 0.8 – 1.0• 'gain' screens: up to 2.0 or more

: typically mid gain (~1.4)

: or high gain (~1.8)

: above 1.8 gain risk of 'hot spotting'

Page 15: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Gain vs. viewing angle

•with all screens, perceived brightness reduces as viewing angle increases

•brightness of gain screens reduces more than matt white as viewing angle increases

Page 16: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Gain curves of typical screens

Page 17: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Benefits of 'gain' screens

• can achieve higher brightness level with lower lamp power

• with very large screens it may be essential to use gain screen to get SMPTE level brightness

• with digital projection, screen gain helps achieve brightness level

Disadvantage – gain screens have a narrower viewing angle than matt white screens

Page 18: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

•This theatre has most seats with an acceptable viewing experience.

Viewing Angle

Page 19: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen type/lamp power

       

 

    

Parameters that can affect the presentation

lamp power vs. screen gain

Screen width (m)

Cinemascope format9 12 15 18

Screen gain level

1.0 flat

1.5 curved

1.8 curved

lamp kw required

1900 3400

2700

2100

5300

4200

3300

7600

6000

4700

Potential financial benefits of gain screens:

lamp costs and power savings

Page 20: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen size/screen type

Harkness recommend the use of different screen gain levels according to screen width:

35mm projection/scope picture• up to 35' (11m) – matt white (1.0)• 35' to 45' (14m) – mid gain (1.4)• over 45' (14m) – high gain (1.8)

Page 21: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen size

Choosing the appropriate size of the screen is important

• absolute size is not the issue• screen size relative to auditorium size and

viewing distance is the important consideration

• optimum screen width gives a subtended horizontal angle from "reference" seat of about 45°- 50°

Page 22: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen Size

•Optimum subtended angle 45-50 with cinemascope picture

•A screen with a larger angle may reduce picture quality

•A lower angle makes the screen seem small, particularly in large auditoriums

Page 23: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen shape

General guideline is that:• matt white screens should be flat• gain screens should be curved

Page 24: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen shape

•Light scattered by a matt white screen can fall on another part of the screen if it is curved, potentially reducing contrast.

•Matt white screens should therefore be flat.

Page 25: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen shape

A curved gain screen reflects more light back to the audience

Page 26: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen shape

•Gain screen curvature

Harkness guideline is 5% curve

R.O.C. = 5% of chord

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Screen shape

• curving a large screen may also be desirable to increase audience involvement

• with a curved screen it is recommended to use a gain screen

Page 28: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screen rake

•With stadium seating, raking the screen may be beneficial

•Each 1 rake gives 2 improvement in reflected light angle

•A rake of more than 5 is not recommended

Page 29: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Acoustic performance of cinema screens

• screen blocks sound from behind screen speakers

• particularly affects high frequencies• screens are therefore perforated• perforation pattern is important

- optimise acoustic performance

- be invisible at closest viewing point

Page 30: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Acoustic performance

Screens can be perforated with different hole sizes and perforation patterns

• Typical commercial cinema screen perforation pattern

1.0 – 1.2mm diameter holes (0.04" – 0.048")

5% open area• For closer viewing (<5m/16')

0.5 – 0.6mm holes (0.02" – 0.024")

2% – 5% open area

Page 31: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Perforation Size and Density

Standard Perf Mini Perf Mini Perf Super 1.2mm diameter 0.5mm diameter 0.5mm diameterDensity 5.5% Density 1.7% Density 4.9%

Page 32: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Sound attenuation of different Harkness perforation patterns

Page 33: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Other important screen characteristics

As well as brightness and acoustic performance, these other screen characteristics are also important:

• colour rendition- accurately portraying colours

• contrast - preserving the contrast variations of the film

• no visible seams or other imperfections

Page 34: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Picture formats/maskingMost common movie formats

are:• Cinemascope 1:2.35• Widescreen 1:1.85

Screen size can be adjusted by• keeping screen height

constant

or

• keeping screen width constant

1

1

2.35

1.85

Page 35: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Picture formats

Constant screen height is optically better:• 1.85 film frame is smaller than 2.35 • less light reaches screen (all other things being

equal)• with constant height, 1.85 is the smaller screen• consequently, light levels are about the same for both

picture formats

With constant width:• 1.85 screen is bigger than 2.35 screen• in this case, less light has to cover a bigger screen

Page 36: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Picture formats

Constant screen width is popular because can use available height better:

• with stadium seating• in small auditoria

However, it is optically worse:• correct light levels are harder to achieve for both

formats 1.85 and 2.35

Page 37: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Picture formats

With constant screen width

• must have sufficient light for 1.85

• use gain screen if large• 'lose' light for 2.35 (to avoid excessive brightness)• adjust lamp current or defocus lamp • use variable aperture lens

Page 38: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Frames and masking

Moving masking is often used to give a sharp edge to each format

• constant height: moving side masking

• constant width: moving top and bottom masking– or moving top masking alone

• if moving masking passes in front of speakers– use acoustically transparent cloth

Page 39: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screens for digital cinema: 2k projectors

• SMPTE brightness standard 14 ft-lbts (16 ft-lbts for 35mm)

• generally follow same guidelines as for 35mm projection

screen <11m (35ft) use matt white screen

screen <14m (45ft) use 1.4 gain screen

screen >14m (45ft) use 1.8 gain screen

• light distribution is more even with 2k projectors – less hot spot risk

Page 40: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

2k projectors : film formats

Changing film formats can be achieved by different means:

•with “constant height” can do this electronically by reducing the area of DMD that is used

• not all available light from projector is used

Page 41: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

2k projectors : film formats

• alternatively using an anamorphic lens for ‘scope’ picture

•this maximises the use of available light

•requires activation of anamorphic lens

•these anamorphic lenses are expensive

•this is the only practical approach on large cinemascope screens

Page 42: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

2k projectors : film formats

•Changing film formats on ‘constant width’ screens

•This is easily achieved electronically

•With digital projection, light is reduced changing from 1.85 screen to 2.35 screen, but so is the screen size. Brightness levels are maintained.

Page 43: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

D-Cinema brightness levels

• depending on the method used, available light varies and therefore screen brightness

• lamps in 2k projectors are expensive (particularly the special short-arc xenons)

• using gain screens can compensate for light losses

• gain screens can be used with standard lamps – saving on lamp costs

Page 44: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

E-Cinema projection

• there are no standards for E-Cinema• brightness level is usually the main issue• gain screens are usually advantageous• depending on projector lumens/screen size,

gain screens from 8m may be necessary• pixilation interference may also be a problem

(moiré) – use a different perforation pattern

Page 45: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screens for 3D

• digital technology gives very high quality 3D with single projector

- can also use film with 2 projectors• most popular technology uses polarised light

- “passive” system• requires ‘silver’ screen to maintain polarisation

- 130:1 extinction ratio (linear polarisation)

- also polarised glasses are needed

Page 46: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Screens for 3D cont’d.

• alternative technologies- “active” system uses moving shutter

glasses- “passive” system uses colour filters

with special glasses• all 3D technologies lose at least 75% of

available light- normally need gain screens

• can use 3D screens for 2D movies

Page 47: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Maintenance of cinema screens

• in clean environments screens should last 7-10 years

• install screens in clean dust-free conditions- all fit-out should be completed beforehand

• periodic soft brushing of screens (vertically)• do not wet screens or use chemicals

Page 48: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Replacing Screens in existing cinemas

• consider screen replacement if

- screen is dirty

- light levels are low

- screen has visible seams or other imperfections

• new screen likely to give significant improvement

- particularly when large matt white screens changed to gain screens

Page 49: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

SummaryScreen can significantly affect movie-going

experience in terms of• picture quality• acoustics/sound qualitySpecification and choice of screen is critical• manufacturing quality• gain level • screen shape (flat/curved)• relative size to auditoria• special performance requirements (e.g. 3D)

Page 50: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Cost consideration

• screen surface cost is low part of total fit-out costs

• difference in cost between good screen and bad screen is 1-2% of fit-out costs

• potential lamp cost and operating savings from using brighter (gain) screens

Page 51: Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

Final thought

• Movie-goers spend less than 30 minutes in foyer areas

• they may spend 2-3 hours looking at the screen

• money spent on optimising screen performance is well worthwhile!