Journal of the Society of Motion Picture Engineers (Volume 55) online

the fact that most films show compression effects in that range. Print
characteristic curvatures between the densities of fog level and 0.4
are usually too great to be tolerated by a system which increases that
curvature. Of course, there are printing systems which depend upon
a balance between a long curved negative characteristic and a com-
plementary print curve. In this case, the above statement may re-
quire modification, but it is believed that very little printing is done in
this manner. When "normal" printing is used, best results will be ob-
tained if the significant densities are placed in the range from 0.4 to



1950 TV FILM SPECIFICATIONS 151

1.9, with only unimportant areas or areas lacking detail permitted to
fall outside these limits. In cases where large black areas must appear
at the bottom of the frame or where black backgrounds are required
for short periods of time, a further reduction in density of these black
areas is recommended. A maximum density value of 1.5 in these areas
is more appropriate if flare and the resulting bleeding of the black are
to be held to a minimum. Ordinarily such a background will be re-
produced as black on the television system, since the original intention
will be obvious to the video operator.

Many film producers have requested specifications on film stocks
and development gammas rather than a required range of densities.
It has not been possible to make any firm statements of this type for
the following reasons:

Gamma is the parameter for which most specification requests are
received. Without any information other than the question, ^'What
gamma is best for television films?" no answer can be given at all. The
term "print gamma" usually refers to the value of the slope of the
density vs. exposure curve for a particular stock developed under some
particular conditions. Usually it is read at the high-density end of
the curve. When this is done an excellent measure of the effects of
development is obtained, but with very little information concerning
the appearance of the picture. As a tool for processing control, print
gamma is excellent, but the picture density range is usually not
"read." Thus two films may be handled so that their IIB densities
may be plotted as straight lines from values of 1 to 2.5, but exhibit
entirely different characteristics below that range. They would both
have the same "gamma," as far as quoting a number is concerned,
making such a quote an extremely unreliable basis for judging picture
quality.

Again, if a negative is low in contrast, a higher print gamma is re-
quired than if it were "normal." Both of these conditions can produce
good pictures, as can the case for a high contrast negative and a low
gamma print. Obviously, some knowledge of the negative develop-
ment would be required for print gamma specification.

"Print-through-gamma" is also an elusive quantity. Curve slopes
are never read in the actual picture range, especially since evaluation
of gradients in that range is difficult. The net result of combining
two gammas is dependent, therefore, on the curve shapes, as well as
the exact portions of those shapes actually used. Even when a pro-
ducing company has arrived at standard developments for negatives
and positives, the assignment of a particular print-through-gamma is
dangerous because of variations in the original scene contrasts and in
negati ve'exposure .



152 CHARLES L. TOWNSEND August

Most film that is good for television use has employed a restricted
scene brightness range. This does not mean "flat" studio lighting.
All the accent lighting used so effectively by Hollywood can and
should be retained. But the ratio of that light to fill-light must be re-
duced. Again it becomes a problem of fitting the scene into final print
densities which can be faithfully reproduced. If it is judged that for a
particular scene the brightness ranges that are high in value are the
most important, then it may be that large values of back-light and
high-light can be tolerated, and the densities representing these
brightnesses must be printed within the range. But if it is judged
that for another scene the low- value brightnesses are most important,
then high-lights must be sacrificed, and exposure increased to get the
print densities down within the specified range. If 100- or 200-to-l
films are made, only disappointment can result from compressing
them into a 30-to-l channel.

Many television films are made outdoors with enormous scene
brightness ranges, and yet produce excellent results. Some of these
films actually show a print density range of 3. This case is a good ex-
ample of the above reasoning. If the wide range film is mostly small
detail of trees, rocks, etc., the video signal will show no texture in the
blacks or whites, but none is needed, since these areas are "texture"
in themselves. As soon as a medium shot or close-up requires detail
in light or dark areas, those areas must be protected from compression
by placing them within the specified range. If the large range is
maintained, faces will become blank white, and dark horses become
animated charcoal drawings. Judicious use of reflectors or fill-light
of any kind will reduce the range of most outdoor close-ups to permit
the adjustment of exposure to produce the densities required.

From the above it will be seen that many combinations of negative
gamma and print gamma can be made to yield good pictures, de-
pending upon the control exercised in original scene brightness range
and exposure. The final product is a range of densities, which has
been specified; and the means by which an individual producer ar-
rives at those values is largely a function of his own operating condi-
tions.

II. RESOLUTION

1 . Television System Characteristics

The television picture delivered to the home viewer is limited in res-
olution by the bandwidth specified by the Federal Communications
Commission, and by the performance of the equipment utilized. In
general, acceptable sharpness is obtainable under normal circum-



1950 TV FILM SPECIFICATIONS 153

stances. Several studies have been made to determine just how sharp
a picture can be broadcast in the present television channel. Tests
with photographic methods whereby an ideal television system can be
simulated, and the use of actual television equipment of a highly re-
fined type, have both shown that present system standards can de-
liver truly excellent definition. That such results are not always at-
tained can be attributed to the large number of system elements
which are difficult to control. Some of these are discussed below.

Under normal circumstances the amplifiers and circuits of the
television system impose no limitation on the transmission of fine
picture detail. Pickup tubes, however, can exert a large effect on
final picture sharpness. Ideally, such a tube should have full video
voltage output at the highest frequency utilized. That is, the finest
black-and-white detail to be transmitted should produce as much
signal voltage as does any larger area. Present-day pickup tubes do
not completely fulfill this requirement, having a reduced output level
at the frequencies corresponding to fine detail in the picture. Elec-
trical equalization is used to compensate for this effect, but this in-
creases the fine-grain "noise" in the transmitted picture so that large
amounts of compensation are not desirable. Great care must be ex-
ercised to see that the pickup tube is supplied with the best possible
picture, in order that over-all degradation is kept to a minimum, since
any degradation in the picture will be compounded with degradation
in the television system.

Suppose for a moment that an audience will accept without com-
ment a well-defined maximum loss in picture detail at a certain viewing
distance. If a television picture having that loss is viewed in that
manner, acceptable results are obtained. If a film picture having that
loss is viewed in that manner, acceptable results are also obtained.
However, if that film, which is acceptable, is viewed over that televi-
sion system (which in itself is acceptable) seriously degraded and un-
acceptable pictures will result. Neither picture system in itself is bad,
but the combination of the systems adds their individual losses, and
the result is noticeably poor.

This introduces the idea that each element of a picture transmission
system must be assigned its appropriate part of the total permissible
loss. Each such loss must be as small as the state of the art permits.
Good circuit design has reduced amplifier losses to a negligible value,
but the enormous complexity of picture tube design and construction
has not permitted attainment of that degree of perfection in their
operation. It has thus long been good practice to assign the major
portion of the total permissible resolution loss to the pickup tube. A



154 CHARLES L. TOWNSEND August

great deal of research is being devoted to reducing this loss but for the
present it is well to continue to "pamper" the pickup tube.

In live-studio practice it is fairly usual for optical systems to de-
liver to the pickup tube photo-cathode images having limiting res-
olution in excess of one thousand television lines. Under such cir-
cumstances very little degradation is contributed by the optical image,
and the net effective sharpness is that of the picture tube. With
film, however, projected image resolution rarely reaches such a high
value, and the net effective sharpness is below that of the pickup tube
alone. It is interesting to note that live-studio pictures are noticeably
degraded when the optical resolving power drops below 800 television
lines.

Further complicating the resolution problem is the electrical grain
or "noise" inevitable in present systems. If pictures having small
"signal" content (low density range) are fed to such a system, am-
plifier gain must be raised beyond normal limits to regain normal
operating levels. This increases the effect of noise, masking the fine
detail in much the same manner as does the grain in a poorly made
photograph.

Kinescope picture viewing tubes also are pertinent in a discussion of
resolution. Good tubes having fine spots are available, but generally
some loss should be allowed for this device. An effect called "bloom-
ing" is particularly important in film reproduction. Whenever an
excessively wide gray-range is fed into the television system, very
bright white areas are likely to produce high signals which are well
above the general "tone" of the scene. In order to reproduce the
lower signals properly, the voltages must be amplified more than
usual before being fed to the picture tube. In this case the bright
white signals are too high in level for normal operation and those
areas blur, losing line structure and picture texture. A reasonable
balance between "whites" and "blacks" is desirable for maximum
sharpness.

2. Film Capabilities

Having established the resolution needs of the television system, it
becomes possible to define the performance required of film systems
designed for its use. Again, some portion of the total permissible res-
olution loss must be assigned to the photographic medium. But
every effort must be made to match the live pickup sharpness, which
means that very little loss can be so assigned. Photography is an old,
established craft capable of excellent image sharpness, so it seems



1950 TV FILM SPECIFICATIONS 155

reasonable that stringent requirements should be placed upon it,
leaving more leeway for the infant television art.

Quite often it is said that film has such excellent resolution that
there cannot be any problem in its television use. Published values
of limiting resolution for many films seem to confirm this, but a closer
investigation indicates differently. First, it must be remembered
that the film resolving-power ratings are for "cutoff" conditions.
That is, they state the highest value at which any line structure can
be seen. This, of course, is at a very low contrast far too low to be of
any value to the television system. "Contrast" is "modulation" in
the electrical system, and it is possible to plot the response of film in
much the same manner as an electrical system. When this is done, it
is discovered that films have no "flat bandwidth." That is, their
contrast falls off as the size of the elements to be resolved decreases.
If the total photographic system is allowed about 10% loss in contrast
at the maximum television resolution, it is found that its limiting res-
olution value must be well above the television cutoff. As a result of
this, the best 16-mm films will be found to be barely good enough.
As a matter of practical fact, it is exceedingly difficult to realize a res-
olution of 400 television lines with a high value of contrast in an
ordinary 16-mm release print. Such a print includes degradations due
to all the elements of the photographic system, including the effects
of printing. For the present, only the very best products and tech-
niques can be combined to produce a 16-mm print which will not
seriously limit the results obtainable through the television channel.
Whenever feasible, 35-mm film should be used, and in this case also,
the best methods should be followed. Unfortunately, not all televi-
sion stations are equipped to transmit 35-mm film, but if original
shooting is done in that size, good quality can be expected from most
of the larger stations, and the rest can be served by reduction-printed
16-mm versions.

III. SCENE CONTENT

1. Reproduced Area

Reference is made to the Television Test Film of the Society of
Motion Picture and Television Engineers. The projector alignment
section of that film includes an implied standard definition of the area
to be scanned. Many stations now have copies of this film, and it is
believed that following its directions will lead to satisfactory results.
Approximately 1^% of the standard projector frame is cut off in
scanning at the top and bottom of the frame, and the sides are cut by



156 CHARLES L. TOWNSEND August

an amount required to maintain the 3X4 aspect ratio specified by
law. The side losses are not the same for 35-mm film as for 16-mm
film, due to the different film frame aspect ratios.

Alignment chart sections from the 35-mm and 16-mm versions of
the test film can be purchased separately, thereby reducing costs.
Frequent reference to these charts, along with the instruction book
accompanying them, is recommended.

Also included in the above chart is a rectangle enclosing approxi-
mately 65% of the frame area. The lines forming it are placed so as
to produce a 10% border within the televised frame. The area within
the rectangle is believed to be reasonably well reproduced on the home
receiver even when scanning is poorly adjusted and centering is badly
set. Important information should be kept within this area, es-
pecially commercial copy titles or trade-marks.

2. "Busy" Scenes

Care should be taken to insure that a scene being photographed
does not have a high-contrast background that will detract from
foreground action when the picture is viewed on a small screen.
Simplicity seems to be required in backgrounds for television more
than for theater use, where images are not "crowded" by the frame
size.

3. Shot Sizes

Television has long made good use of close-ups and medium shots.
Small screen sizes are not the only reason for this. The resolution
needed for a close-up is less than for a long shot, merely on the basis
that less fine detail is needed to carry the intended information.
Thus, receiving sets which are mis-tuned or are out of focus will
reproduce close-ups when long shots will be hopelessly blurred.

The above is not intended to eliminate long shots. Establishing
locale and impressions of size are as important as in the theater, but
important details of wide-angle shots should be pointed up with
clever accent lighting and reduction in unimportant competing de-
tail.

4. Scene Tone Balance

Some refinements in smoothness of reproduction can be obtained
when large black-and-white areas are needed, if they are used with
care. Half-black, half-white pictures, with the dividing line running
horizontally, usually require relatively large shading corrections.
This is particularly true if the lower half of the picture is black. Sea-



1950 TV FILM SPECIFICATIONS 157

scapes or any sky and land scene can fall into this category if no large
foreground objects are available to break up the pattern. Also, sudden
large changes in scene brightness should be avoided, as they place
severe requirements on both transmitter and receiver "d-c insertion"
performance. Smooth changes or small steps are usually reproduced
without trouble. Cutting between shots of an object which have
radically different background brightnesses can cause the object itself
to appear to change tone, becoming darker with the light background,
and lighter with the dark background. Avoid if possible the use of
full daylight shooting of night scenes when the required effect is pro-
duced by purely photographic means. "Blacks" look severely com-
pressed in that case, and video operators tend to raise their brightness
control to bring out what may be there, but is not. If possible, al-
ways include some full-level high-light to define the "white signal"
limit. Usually this can be done without harming the scene mood for
direct projection and will greatly aid in television transmission.

APPENDIX : RECAPITULATION OF SPECIFICATIONS

1. Density. Normal contrast range, 1.5; minimum density, 0.4; and

maximum density, 1.9.

2. Gamma. No exact statement possible, but generally the above will

require that gamma be somewhat lower than usual in films in-
tended for theater use.

3. Resolution. Limiting value, minimum, 800 television lines.

4. Scene content

Follow : SMPTE frame-size specifications in the Television Test
Film.

Avoid : Sudden large brightness changes, large black areas near
frame edges, "busy" backgrounds, too great gray range, arti-
ficial night shots.

REFERENCES

1. Otto Schade, "The electro-optical characteristics of television signals," RCA

Rev., (Publication #ST353, Tube Dept., Harrison, N.J.), 1948.

2. R. B. Janes, R. E. Johnson and R. S. Moore, "Development and performance

of television camera tubes," RCA Rev., vol. 10, no. 2, pp. 191-233, June 1949.

3. D. R. White (Chairman), "Films in television," Jour. SMPE, vol. 52, pp. 363-

379, Apr. 1949.

4. G. D. Gudebrod, "Television-film requirements," Jour. SMPE, vol. 53, pp.

117-119, Aug. 1949.

5. A. J. Miller, "Motion picture laboratory practice for television," Jour. SMPE,

vol. 53, pp. 112-113, Aug. 1949.

6. The Use of Motion Picture Films in Television, 56 pp., Eastman Kodak Co.,

Motion Picture Film Dept., 343 State St., Rochester, N. Y., 1949.
See also: "Television test film," Jour. SMPTE, vol. 54, pp. 209-218, Feb. 1950.



A 100,000,000 Frame Per Second
Camera

BY M. SULTANOFF

TERMINAL BALLISTIC LABORATORY, ABERDEEN PROVING GROUND,
MD.



SUMMARY: Shock waves close to the edge of explosive charges have been
successfully photographed at rates exceeding 100,000,000 frames/sec.
These ultra high framing rates are obtained with a multi-slit focal plane
shutter which is transported optically across the film plane by a rotating
mirror. Linear shutter speeds up to 3,000 meters/sec are easily obtained,
and the resulting framing rates with the proper selection of slit widths can be
varied from 10 5 to 10 9 frames/sec. Each individual frame is composed of a
series of lines, and the degree of "discontinuity" across each frame is pro-
portional to the total number of frames.

THE EXPERIMENTAL STUDIES of the shock and detonation which
accompany explosive reactions have been hampered by the lack
of ultra high-speed instrumentation. Short duration optical studies
are particularly required for the investigation of self-luminous detona-
tion and shock waves.

The velocity of these transients averages about 8 mm per micro-
second; therefore, usable photographic exposures of these transients
must not exceed 10 ~ 7 sec. Kerr cell shutters 1 have been used to ob-
tain a single or a few successive short duration exposures, while
multi-lens cameras 2 have produced continuous short duration ex-
posures, but at rates which are not adequately high. The O'Brien-
Milne camera, 3 which is rated at 10,000,000 frames/sec, but which
displays poor resolving power, could not be obtained commercially,
and its precise optical system made it impractical to build locally.

A motion picture camera which employs simple optical and me-
chanical systems to obtain up to 300 successive 4 X 4 in. frames at rates
which can be varied from 10 5 to 10 9 frames/sec, and which exhibits
satisfactory resolving power, is described in this paper.

THEORY OF GRID FRAMING

The standard variable slit focal plane shutter in common use ex-
poses a time-space record as it travels across the film plane. Al-
though the slit moves slowly across the film, the exposure time can be
made extremely short by reducing the width of the slit.

PRESENTED: April 26, 1950, at the SMPTE Convention in Chicago.
158 AUGUST 1950 JOURNAL OF THE SMPTE VOLUME 55



100,000,000 FRAMES PER SECOND



159



The framing grid is a focal plane shutter with a series of parallel
slits placed at regular intervals across it. This shutter, therefore, is
required to move only the distance between two successive slits to
expose the entire film. To understand how this grid records suc-
cessive frames, consider a series of optically clear slits .0005 in. wide,
cut at .015-in. intervals across a 4 X 4 in. optically opaque plate.
If this grid is held in a fixed position on a 4 X 5 in. photographic plate,




Fig. 1. Single still photograph of spherical charge in firing
position, taken through .0005-in. slit, .015-in. space grid.

a single exposure made through it would consist of a set of parallel
lines which occupy only ^Q of the total picture area with an over-all
dimension of 4 X 4 in. A sample exposure of this type is shown in
Fig. 1. By moving the grid across the film perpendicularly to the
slits for a distance of .0005 in., and exposing a second still picture in
this new position, a second series of lines lying alongside the first set
and again occupying only ^ of the total picture area will be pro-



160



M. SULTANOFF



August



duced. Thirty such single pictures will result from only .015-in. move-
ment of the grid, and will expose the entire film area. To the casual
observer the resulting picture will be an indistinguishable jumble.
However, by proper positioning of the grid, any one of the 30 ex-
posures can be studied separately. This type of grid framing has
been used for years in animated greeting cards and photographic ad-
vertisements.

If the photographic object is moving, and if the grid is moved at a
uniform rate across the film for a distance of .015 in., the resulting
picture can be viewed through the grid as 30 separate exposures, one
at a time, or, by viewing through the grid moving at any uniform



ROTATING MIRROR





CHAROE



OSCILLOGRAPH



-o


SIGNAL




GENERATOR







Fig. 2. Synchronizing circuit for ultra high-speed camera.

speed, flickerless motion pictures will be observed. This adaptation
of grid framing has been described in papers delivered by Dr. Fordyce
Tuttle of the Eastman Kodak Co. 4

At this laboratory we have been successful in combining a stationary
framing grid with a rotating mirror to obtain framing rates in excess
of 10 8 frames/sec.

THE ROTATING MIRROR GRID COMBINATION

The optimum slit width for the multi-slit focal plane shutter ap-
pears to be of the order of .0001 in. A shutter with .0001-in. slits
is required to move 10,000 in./sec to produce 10 8 frames/sec. It is



1950 100,000,000 FRAMES PER SECOND 161

impractical to accelerate to, maintain, and decelerate from, such
high velocities with a linearly moving shutter. A rotating focal
plane shutter, on the other hand, has the double disadvantage of re-
quiring tapered radial slits and the combination of a large diameter
and high rotational velocity. A method for moving the image of the
shutter across the film plane by reflection from a rotating mirror was
obviously a simple solution to this problem. The rotating mirror
optical system in a Bowen RC-3 Rotating Mirror Camera, 5 although
not adequate for this application, was available at this installation,
and it was modified to take a 4 X 4 in. multi-slit framing grid and a