A CINEMA PROJECTOR FOR 70 mm AND 35 mm FILMS

A CINEMA PROJECTOR FOR 70 mm AND 35 mm FILMS

APRIL 1956 299 A CINEMA PROJECTOR FOR 70 mm AND 35 mm FILMS 778.554.1 In the last few years various new systems of making and projecting films hav...

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APRIL

1956

299

A CINEMA PROJECTOR FOR 70 mm AND 35 mm FILMS 778.554.1

In the last few years various new systems of making and projecting films have heen used. Philips is indirectly involved in one of these, viz. the Todd-AD.1) system. The American Optical Company, the firm that undertook the development 'of the "Todd-A.O." system turned to Philips in Eindhoven for the development; and manufacture of the necessary special projectors. We shall deal hriefly with the "Todd-A.O. system" and its position in regard to two other well-known new systems, namely "Cinerama" and "Cinemaêcope", hefore turning to the proj ector itself. The aim of these new systems is to strengthen the impression of "realness" created hy the film. The method used in the ahove threesystems is to photograph a wider field of view hy using wide-angle taking lenses and to take up more of the field of vision of the audience with the projected picture hy widening the screen. It is not sufficient to fill the higger screen hy projecting a normal film that has heen enlarged still further; this would only produce the same effect as if the audience were to sit nearer to the screen. It is most desirahle to combine the use of a wide screen with stereophonic sound. The positions on the screen where the actions take place now vary so much that it would he distracting were the accompanying sound to come from just one fixed direction. Increase in the picture angle at the filming stage has heen taken furthest in the "Cinerama" system. In this system three cameras are used which take adjoining pictures, and this gives a total picture angle of 146° in filming. When these are projected, a wide curved screen is used on which the three films are projected next to each other (fig. 1) hy three synchronized projectors. It is true, as can he seen from fig. 1, that the great majority of the audience will see the picture at an angle considerahly less than 146°, hut experience shows that this is not ohjectionahle. The success of "Cinerama", which in Europe has heen seen in London, Paris, 'Milan and Rome, was so complete that audiences accepted the shortcomings of the system. Fiom the audience's point of view the greatest ohjection is that the two dividing lines on the screen where the pictures join, have not yet heen successfully eliminated. The brightness and colour of the three pictures are never absolutely alike. Móreover, every picture projected dances a little: the position of the frames on the film and the transport mechanisms of the projectors are never 1) Todd is the name of the man who advocated the system; A.D. stands for "American Optical Company".

quite perfec~ and this means that consecutive frames never occupy exactly the same position in the film gate. The dancing effect is not the same for each of the three films so that they can he seen to quiver with respect to each other at the picture houndaries. Possibly even more distracting is the fact that at a picture houndary the faults in the picture, though slight; change in a discontinuons manner. This can cause, for example, a long ohject situated across the width of the screen to show a kink at a picture houndary. This is especially an~ noying when an ohject of this kind (e.g. a hoat)

86207

Fig. 1. Schematic diagram of the Cinerama system, showing the arrangement of the screen S, the three projectors PH P2 and P3 in their projection rooms Cl> C2 and C3, and the audience A.

moving right houndary.

across the screen, passes a picture

From the point of view of the cinema management, "Cinerama" has the further disadvantage that the three projection rooms have to he placed in the auditorium itself, so that a considerahle number of seats have to he given up to make room for them (fig. I). Projection is not possible from rooms situated high up as the light heams would strike the screen obliquely and horizontal lines for instance would he reproduced as curved ones hecause of the curvature of the screen. Moreover, the whole arrangement is very complicated and several technicians are necessary to operate it. It is understandable that other systems have heen . tried with a view to achieving the desired effect while avoiding the difficulties mentioned. An elegant approach to the -problem was made possible hy the development of a special wide angle

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17, No. 10

In fig. 2 we have a strip of 70 mm film~and in objective by Professor Brian O'Brien of the fig. 3 strips of normal 35 film and of 35: ~mlfilm American Optical Company. This lens has a 0 for "Cinema.Scope". In all the films the perforations picture angle of 128 (but nevertheless has a have the same spacing. With the 70 mm film, howcornparatively large numerical aperture). A film ever, the height of the frame is 5 times the pel-forataken with this lens consequently covers an area only slightly less than that of the three "Cinerama" cameras combined. Such a film can be projected on to a wide, curved screen and this produces, with a single projector, a similar effect to that of "Cinerama". Incidently, the "picture angle" of the projector does not need to be made specially large. This special objective forms the nucleus of the "Todd-A.O." system, but the system has other characteristic features. One of these is that it has completely broken with tradition by using 70 mm film in place of 35 mm and at the same time the frame frequency has been increased from 24 to 30 frames per second. The higher frame frequency produces smoother motion and lessens flickering in the picture reproduced on the screen. This is very desirable, for the eye is most sensitive to flickering at the periphery of the field of vision and, as a result, flickering on a wide screen might become noticeable. Fig. 2. Strip of 70 mm film. It has six magnetic sound-tracks, The problem of obtaining a sufficiently bright three on either side of the film. The wide hlack bands on the outside of the perforations carry two sound-tracks each; the picture on the large screen is greatly simplified by narrower bands inside thc perforations carry only one each. the wide film, since the area of the frame on 70 The height of the frame is equal to 5 perforations. mm film can be made 3.5 X as large as that on nortion spacing whereas it is only 4 times with 35 mm mal 35 mm. For the same luminous intensity on the film; this means that the frame on the wide film is film, 3.5 times as much light strikes the screen. not only wider but also higher than that on normal In addition, the higher frame frequency contributes film. In contrast with "CinemaScope", the scene to less heating of the film. is photographed on the film in natural proportions. Another important advantage is that the big The shape of the projected picture therefore corresscreen can be filled without abnormally large ponds to that of the frame (the film mask is 48.5 magnification. With the small frame of 35 mm film, by 22 mm) and a so-called anamorphic projection the grain of the film emulsion would be visible and lens (as in "CinemaScope") is not used. would tend to blur the image.

a

b

c

Fig. 3. Strips of 35 mm film (a) normal and (b and c) "CinemaScope". The normal 35 mm film has one optical sound-track; the 35 mm "CinemaScope" film has either four magnetic sound-tracks, two on either side of the film (b), or one optical sound-track (c). Only in the second case (b) is stereophonic reproduetion possihle.

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In "CinemaScope", for which many cinemas have already been adapted, 35 mm film is used. By means of the anamorphic lens used in this system, the picture is compressed in a horizontal sense (fig. 3b and c) when being taken. When the film is being projected the picture is expanded horizontally by a similar lens, so that the natural relationships are restored. The relationship of width to height of the projected picture can be larger by these means than it actnally is on the film. The picture angle during shooting is about 900 as compared to 1460 for "Cinerama" and 1280 with "Todd-A.O.".

On the wide film there is room for the six magnetic sound-tracks which give well-nigh perfect stereophonic reproduction. (A magnetic soundtrack can give a higher quality of reproduetion than an optical sound-track). Behind the screen there are five groups of loudspeakers, whilst in the auditorium there is a further number of loudspeakers used for special sound effects. Each group is supplied by its corresponding sound-track. It is now not necessary to have the six sound-tracks on a separate synchronously driven film as is the case with the "Cinerama" system. The greater frameheight and the higher frame-frequency combined, increase the film speed by a factor 5/4 X 3°/24 = more than 1.5 times over that with normal film. This improves the quality of the sound: high frequencies can now be better recorded and reproduced.

Fig. 5. Path of film when projecting either 70 mm or "CinemaScope" (35 mm) with magnetic sound-tracks. The projector in the figure is threaded with 70 mm film. After leaving the upper spool A, the film is fed past the magnetic sounel head B. The film then passes to the take-up spool E via the curved film guide C, by-passing the optical sound head D. If normal 35 mm film or "CinemaScope" film with an. optical soundtrack is being projected, the film by-passes the magnetic sound head and is fed past the optical sound head.

The projector

Fig. 4. The 70 mm film projector (type EL 4000) which at the same time is suitable for projecting normal 35 mm and "CinemaScope" films (with 4 magnetic sound-tracks or with one optical sound-track).

As already mentioned, the special projector for the "Todd-A.O." system has heen developed in Eindhoven and is now being manufactured there (Type EL 4000). The projector is so made that it is suitable not only for the new system but also for normal and for "CinemaScope" films. A cinema adapted for "Todd-A.O." is, with one type of projector, equipped for most other current projection systems at the same time (not, of course, for "Cinerama".) Fig. 4 is a photograph of the projector. The projector has an optical sound head (for the optical sound-tracks on 35 mm film) and a magnetic sound head for 35 mm "CinemaScope" film and for 70 mm film. These heads are so arranged that the film can by-pass the heads not in use (fig. 5). The magnetic sound head has a total of 10 pick-ups (fig. 6); 6 of these correspond to the sound-tracks of 70 mm film and the other 4 to the sound-tracks on "CinemaScope" film (35 mm). The sprockets have 4 toothed rims; the inner two are used for transporting 35 mm film, the outer

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Fig. 6. The magnetic sound head of the EL 4000 cinema projector. 10 pick-ups can be seen as narrow ridges projecting from the mount. The four in the middle, which are those corresponding to the sound-tracks on "CinemaScope" film (35 mm), do not project quite as far as the others so that when 70 mm film is being projected they cannot cause any damage.

two for 70 mm film (fig. 7). The film is drawn forward by a 4-slot Maltese cross mechanism and the intermittent sprocket must therefore have a periphery equal to 4 times the size of the frame 2). As already stated, the height of the frame in 70 mm film is 5/4 times that of 35 mm film. The periphery, and consequently also the diameter of the intermittent sprocket must differ by this same factor for the two sizes of film. Hence the 70 mm film is clear of the sprocket teeth for 35 mm film.

Fig. 7. Sprocket for 70 mm and 35 mm film. The toothed rims in the centre (for transporting 35 mm film) are set deeper so that they clear the 70 mm film.

2) See Philips

tech. Rev. 16, 158-171, 1954/55.

REVIEW

VOL.

17, No.

10

The sprocket shown in fig. 7 is the type used both for the take-off sprocket and for the take-up sprocket, which respectively draw the film at uniform speed from the feed spool and lead it on to the take-up spool. The diameters of the toothed rims for 70 mm and 35 mm film also differ by a factor of 5/4 but the peripheries are six times the size of the frame. When transferring from one film size to the other, some re-adjustments have to be made: e.g. the film guide (which guides the film at the gate, see fig. 5) and the pad rollers (which keep the film on the teeth of the sprockets) have to be changed. In addition the speed of the projector has to be changed and for 'thispurpose the apparatus has 2 motors (visible in fig. 4) and a selector switch. The objective too must of course be the correct one for the projection system in operatien. 70 mm film has a greater tendency than 35 film to buckle in the film gate under the influence of the heat generated by the are lamp. This would cause the projection to .become blurred and so to prevent this, the film guide has been slightly curved.jfig. 5) which gives the film more rigidity at that point. The normal flat pressure springs need now to be replaced by thin steel strips, whose tension:can be adjusted and which press the film tightly to the gate. The projector is fitted with a single-blade rotating shutter and the two interruptions per frame that are necessary are achieved by allowing the shutter to make two revolutions in this period. The effective region of the shutter blade is at the outer edge and at a large distance (about 12 cm) from the point of rotation. This blade interrupts the lightbeam only 12 mm from the film at a point where the diameter of the beam is small. With these measures shutter losses are reduced to 4.6% 3). The high number of revolutions of the shutter (3600 revs/min for 70 mm film) cause the projector to run with more noise than is usual. Also the flapping of the wide film is noisier than that of normal film. This is due to the increased width, the greater frame-shift and the higher frame-frequency. However, when the door of the projector is closed, the noise is not annoying for the operator. The "Todd-A.O." system had its public debut on 13th October 1955 with the film "Oklahoma" shown in the Rivoli Theatre on Broadway, New York. The strip of 70 mm film reproduced in fig. 2 contains a scene from this film. J. J. KOTTE. 3) The high speed of the effective part of the shutter

blade produced by the doubled rotation speed and the large radius of the shut ter, lessen the effect of the so-called "covering angle". A small beam diameter at the point of interception is also favourable in this connection. See article quoted in 2).

APRIL 1956

303

ABSTRACTS OF RECENT SCIENTIFIC PUBLICATIONS BY THE STAFF OF N.V. PHILIPS' GLOEILAMPENFABRIEKEN Reprints of these papers not marked with an asterisk * can be obtained free of charge upon application to the Philips Research Laboratory, Eindhoven, Netherlands.

2227: M. E. Wise: A quickly convergent expansion for cumulative hypergeometric probabilities, direct and inverse (Biometrika 41, 317-329, 1954). Sampling without replacement from finite populations is treated. If n units are taken from a population of N containing Nx defectives, we may want to know the probability P that (say) c defectives or less are found in the sample of N; or, conversely, what is the value of x corresponding to given values of c and P. It was generally believed that' these results were far' more difficult to work out than for the corresponding problem with "infinite batches" in which we do not have to allow for the units removed in the sample as affecting the composition of the rest of the batch; this case only involves binomial probabilities, whilst the finite batch case involves hypergeometric ones. This paper derives simple but accurate approximations for these probabilities and for the inverse case. The mathematical method is an unusual one and is given in full, as it might be usable in quite different problems leading to hypergeometrie series. Two numerical examples are given, in each of which, for given c, points in a pox curve are calculated and compared with the corresponding exact values. 2228: P. F. J. Bogers: Organische stoffen bij demineralisatie (Water 38, 229-302, 1954). (Organic substances in demineralization; in Dutch). Report of investigations into the poisoning of ion-excliange resins by organic substances present in water. 2229* : J. Smit and H. P. J. Wijn: Physical properties of ferrites (Advances in Electronics and Electron Physics 6, 69-136, 1954).

It is shown that the vibrational structure appearing in the luminescent emission close to the fundamental ,absorption bands of ZnS, CdS. and ZnO corresponds to the frequency of the longitudinal lattice vibrations ofthe opticalbranoh. This proves that the edge' emission is a property of the pure, unperturbed lattice. In connection with observations by Klick it is concluded that the fluorescence is due to èxcitons, The appearance of double peaks in the infra-red absorption spectrum of ZnO and BeO is explained by a two-phonon process, involving phonons of the optical and acoustical branch according to a theory given by Born and Blackman. 2231: C. Z. van Doorn: Temperature dependence of the energy-gap in ZnS (Physica 20, 11551156, 1954). The temperature dependence of the energy-gap. in ZnS was determined by direct measurement of the shift of the absorption-edge as a function of temperature. The results were in good agreement with calculations by W. W. Piper and measurements by J. H. Gisolf. 2232: T. Tol: Fundamentale Probleme bei der Röntgen-Kinematographie 'oot Bildverstärker (Research Film, No. 5, pp . .1-6, Dec. 1954). (Fundamental problems in X-ray cinematography with the image intensifier; in German). Brief survey of selected .topics presented in previous article in Philips tech. Rev. 17, 69-97, 1955/1956 (No. 3). 2233: L. A. JE. Sluyterman and The rate of condensation methyl esters in solution Pays-Bas 73, 1001-1008,

H. J. Veenendaal: of some tripeptide (Bec. Trav. chim. 1954). ,

Survey of theory and experimental results concerning the properties of Ferroxcuhe, up to the end of 1953. See also Philips tech. Rev. 8, 353-360, 1946; 9, 185-190, 1947/48; ll, 313-322, 1949/50; 13, 181-193, 1951/52; 16, 49-58, 1954/55; and these abstracts Nos. 2092 and 2109.

The condensation rate of a few tripeptide methyl esters in methanol has been studied at 65 The peptide esters with a glycyl residue at both ends have been found to he equally reactive, regardless of the nature of the amino acid residue in the middle. A side chain situated on one of the terminal amino acid residues decreases the reaction rate:

2230: F. A. Kröger and H. J. G.. Meyer: The edge emission of ZnS, CdS, and ZnO and its relation to. the lattice vibrations-of these solids (Physi~a 20, 1149-1155, 1954).

2234: C. G. J. .Iansen, R. Loosjes and K. Compaan: Distribution anormale des vitesses des électrons émis par une cathode à oxydesen, régime d'impulsions (Le Vide 9, 129-134 1954).

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TECHNICAL REVIEW

VOL. 17, No. 10.

French version of paper published in Philips Res. Rep. 9, 241-258, 1954 (see these abstracts No. R246).

fruit trees cannot live in ivy; and vice versa. Owing to unfavourable weather, experiments to test this hypothesis have not given definite results.

C. G. J. Jansen, R. Loosjes, J. J. Zaalberg van ZeIst and G. A. Elings: Dne méthode oscillographique pour determiner le Potential d'Extraction en fonction de la ,température (Le Vide 9, 135-138, 1954).

2238: J. G. van Pelt and H. Keuker: De electrometrische Karl Fischer titratie (Chem. Weekblad. 51, 97-99, 1955, No. 7). (The electrometric Karl Fischer titration; In Dutch).

2235:

An oscillograph has been developed which describes the saturation emission current is of a diode as a function of the temperature T of the cathode. The curve is described in about ten seconds, during which the anode-cathode voltage remains .practically constant. The temperature T is measured .hy a Pt-PtRh thermocouple connected to the metal of the indirectly heated cathode. As the is = f(T) curve is determined in 'such a short time, the effects of poisoning of the cathode surface are kept to a minimum. Moreover, it is possible to determine very. quickly not only the work function ep of the cathode hut also its temperature coefficient dep/dT from a graph of saturation current density js as a function of absolute temperature, with the help of Richardson's formula. 2236:

A. Venema: Applications de la cathode (Le Vide 9, 269-272, 1954).

L

The construction and working of the L-cathode are described and some of the special precautions necessary in its fabrication are mentioned, The special properties of this type of cathode are then dealt with in connection with the metallic emitting surface (no oxides) and the replenishment of the activating material (barium). The application of the L-cathode in the EC56 disc-seal triode (power amplifier, up to about 4000 Mc/s) is described. Another example of its use is in the 4J50 magnetron, which gives a 250 kW output at a wavelength of 3 cm. The use of the L-cathode in klystrons and in X-ray tubes is also described.

A simple and practical apparatus for electrotitration for the determination of water and a method for quick preparation of the necessary reagents. 2239: N. W. H. Addink, J. A. M. Dikhof, C. Schipper, A. Witmer and T. Groot: Quantitative spectrochemische Analyse mittels des Gleichstrohmkohlebogens (Spectrochimica Acta 7, 45-59, 1955, No. I). (Quantitative spectrochemical analysis by means of the D.C. carhon are; in German). Detailed account of the "Constant Temperature Arc" method of analysis developed in E~dhoven (see N. H. W. Addink and W. de Groot, Philips tech. Rev. 12, 337-348, 1950/1951. The method consists of completely volatilizing 5 mg of a powdered sample in a shallow anodic crater of a carbon are, with the addition of materials to modify the rate of volatilization if required. The linè intensities are calibrated and corrections are made by comparison with selected Fe-lines, originating from a "standard light source" so as to get comparable analytical results; the calculations required are illustrated by several examples which also indicate the accuracy of the method. Tables are given of the empirically . determined K-values, so that they can he checked in other laboratories. 2240: A. Kats and J. M. Stevels: Colour centres in alkali silicate glasses (Z. physik. Chem. 3, 255-260, 1955, No. 3-4).

It appears that the theory of colour centres, caused by X-ray and U.V. irradiation, as developed 2237: J. Meltzer: Morphopogical notes on Bryobia in recent years for alkali halides, also holds for alkali forms of fruit trees and ivy (Entomologische silicate glasses. The effect of such irradiation has Berichten 15, 337-339, 1955). been studied by the changes in the absorption spectrum between 200~ Á and 10000 Á for various Bryobia mites (Bryobia praetiosa Koch) found glasses with different alkali oxide content. The on apple and pear trees appear to differ morphologictheoretical background of the results is briefly . ally and in size from those found on ivy. The author helieves that the two types represent different , discussed; a full account of this work will appear in . species. There a~e indications that those living in Philips Research Reports.