Cinema Screen Specification & Design

2. Cinema Screen Specification & Design Andrew Robinson Managing Director Harkness Screens

3. CinemaScreen 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

4. Choice of screen impacts on the overall experience: picture quality/viewing experience sound quality/acoustic performance It can also affect cinema operating costs

5. 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.

6. 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.

7. 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)

8. 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.

9. 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

10. 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

11. Light reflectance Gain Screen Matt White Screen Gain screens reflect more light back to the audience

12. Measurement of gain Projector Light meter Magnesium carbonate block Screen surface Gain is measured according to British Standard BS 5382

13. Measurement of viewing angle Gain is measured at intervals of 10° by comparison with reference standard

14. 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'

15. 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

16. Gain curves of typical screens

17. 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

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

19. Screen type/lamp power Parameters that can affect the presentation

20. 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)

21. 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°

22. 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

23. Screen shape General guideline is that: • matt white screens should be flat • gain screens should be curved

24. Screenshape • 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.

25. Screen shape A curved gain screen reflects more light back to the audience

26. Screen shape•Gain screen curvature Harkness guideline is 5% curve R.O.C. = 5% of chord

27. 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

28. 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

29. 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

30. 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

31. 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%

32. Sound attenuation of different Harkness perforation patterns

33. 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

34. 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 2.35 1 1.85

35. 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

36. 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

37. Picture formats With constant screen width • must have sufficient light for1.85 • use gain screen if large • 'lose' light for 2.35 (to avoid excessive brightness) • adjust lamp current or defocus lamp • use variable aperture lens

38. 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

39. Screensfor digitalcinema: 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

40. 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

41. 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

42. 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.

43. 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

44. 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

45. 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

46. 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

47. 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

48. Replacing Screens in existing cinemas • consider screen replacement if - screen is dirty - light levels are low - screen has visible seams or otherimperfections • new screen likely to give significant improvement - particularly when large matt white screens changed to gain screens

49. 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)

50. 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