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
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/m 2 ) 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 screens reflect more light back to the audience Gain ScreenMatt White Screen
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
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
This theatre has most seats with an acceptable viewing experience. Viewing Angle
Screen type/lamp power Parameters that can affect the presentation lamp power vs. screen gain Screen width (m) Cinemascope format 9121518 Screen gain level 1.0 flat 1.5 curved 1.8 curved lamp kw required 19003400 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 Mini Perf Mini Perf Super 1.2mm diameter 0.5mm diameter 0.5mm diameter Density 5.5% Density 1.7% 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 or keeping screen width constant 1 1 2.35 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 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 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 contd. 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 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
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!