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 moviegoing experience
• presentation relates to 35mm projection but
will also cover digital cinema
Choice of screen impacts on the overall
experience:
• picture quality/viewing experience
• sound quality/acoustic performance
It can also affect cinema operating costs
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.
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.
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)
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.
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
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
Light reflectance
Gain Screen
Matt White Screen
Gain screens reflect more light back to
the audience
Measurement of gain
Projector
Light meter
Magnesium carbonate block
Screen surface
Gain is measured according to British Standard BS 5382
Measurement of viewing angle
Gain is measured at intervals of 10° by
comparison with reference standard
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'
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
Gain curves of typical 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
Viewing Angle
•This theatre has most
seats with an acceptable
viewing experience.
Screen type/lamp power
lamp power vs. screen gain
Screen width (m)
Cinemascope format
Screen gain level
1.0 flat
1.5 curved
1.8 curved
9
12
15
18
lamp kw required
1900
3400
2700
2100
5300
4200
3300
7600
6000
4700
Potential financial benefits of gain screens:
lamp costs and power savings
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)
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°
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
Screen shape
General guideline is that:
• matt white screens should be flat
• gain screens should be curved
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.
Screen shape
A curved gain screen reflects more light back to the audience
Screen shape
•Gain screen curvature
Harkness guideline is 5% curve
R.O.C. = 5% of chord
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
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
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
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
Perforation Size and Density
Standard Perf
1.2mm diameter
Density 5.5%
Mini Perf
0.5mm diameter
Density 1.7%
Mini Perf Super
0.5mm diameter
Density 4.9%
Sound attenuation of different Harkness
perforation patterns
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
Picture formats/masking
Most common movie formats
are:
• Cinemascope 1:2.35
• Widescreen 1:1.85
Screen size can be adjusted by
• keeping screen height
constant
1
2.35
or
1
• keeping screen width constant
1.85
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
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
Picture formats
With constant screen width
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•
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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
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
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
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
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
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.
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
E-Cinema projection
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•
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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
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
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
Maintenance of cinema screens
• in clean environments screens should last 710 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
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
Summary
Screen can significantly affect movie-going
experience in terms of
• picture quality
• acoustics/sound quality
Specification and choice of screen is critical
• manufacturing quality
• gain level
• screen shape (flat/curved)
• relative size to auditoria
• special performance requirements (e.g. 3D)
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
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!