Download Report - Academy of Motion Picture Arts and Sciences

of existing lens equipment and on his expectations
of future developments.
The demands of the motion picture industry have
driven the lens manufacturers to attempt to supply
lenses of a relative aperture which twenty years ago
would have been regarded as impracticable. Progress
in this direction has been attended by much
efiort and expense. It is very doubtful whether
the profits on all the high speed lenses sold are equal
to the money which has been spent in design. But
with all the effort, no essentially new principles of
lens design have been involved. There is no lens
construction in use today which could not have been
produced twenty or more years ago if the designer
had had the courage to attempt the task, or any reason
to believe that there would have been {ound any
useful application of the type o{ lens he could have
produced.
The short focal lengths required in motion picture
work and the pictorial character of the work
are the factors which have made reasonably high
speed lenses possible. The definition in the image
formed by any lens depends upon the residual aberrations
which still remain after the designer has
done his best with the correction. In general, all
lenses of a series of focal lengths sold under the
same name are geometrically similar. That is, the
radii of curvature of the surfaces, the thicknesses of
the component lenses, and the separations of the
lenses are usually all exactly twice as great in a 6-
inch as in a 3-inch of the same series of lenses. It
follows that the numerical value of the aberrations
is proportional to the focal length and that it may
be easily possible that the quality of image produced
by a 2-inch lens may be satisfactory while a 6-inch
of the same type might be regarded as useless. Early
photography did not use 2-inch lenses, hence the
designer was wise in regarding F:2.0 lenses, for
example, as impractical. Further, in the early days
of the anastigmat nothing was regarded as acceptable
other than the sharpest possible definition. This
attitude has fortunately been abandoned by everyone
but photo-engravers, scientists, engineers and
others whose work requires for its success the closest
possible approach to absolutely sharp definition.
There is no doubt that absolute sharpness of definition
is undesirable in pictorial photography. There
is an equal degree of certainty in the mind of the
speaker that both in portrait and motion picture
photography the departure from sharp definition
has been carried too far to please the general public.
There is no doubt that this has been the result
of the enthusiasm with which we are all prone to
receive any new thing, using it without discretion
until our appetites are jaded and we relapse into
boredom unless another novelty takes its place. On
the other hand, while the question of the extent to
which definition should depart from perfection is
debatable there is probably no dissent from the general
proposition that a certain amount of softness
enhances the pleasure we derive from any photograph
intended to appeal to our sense of beauty.
These two facts have made the fast lenses possible.
If a higher degree of definition be demanded
of the fast lenses it can be attained only by complicating
the construction and thereby reducing the
realizable, efiective speed' The economic law of
"diminishing returns" applies to lens'design as well
as to agriculture or to selling efiorts. A general
demand for better definition than is now possible
can be met only by lenses of lower relative aperture'
by lens constructions so complex that the ultimate
result is equivalent to lenses of lower aperture, or
by new discoveries in the realm of lens design and
manufacture. In fact, it is reported that existing
high speed lenses fail to show exposures commensurate
with their relative apertures.
Twenty years ago a relative aperture o{ F:4.5
was regarded as very high for anastigmat lenses.
When such lenses were applied to photography it
was found that fore-ground and back-ground fell
out of focus very rapidly for all but very long shots.
This marked lack of depth of focus was seized upon
by the salesmen as a mark of superiority' They
claimed it added depth or plasticity, stereoscopic
efiect, to present the principal object in sharp focus
against an out-of-focus back ground, making a virtue
out o{ a defect, as salesmen in all lines of merchandise
are prone to do. The public accepted this
view for a time, but the public is today more inclined
to independent judgment as to what is good
and bad photography, having been largely educated
therein by the marvelous accomplishments of the
cinematographers. The public today is not pleased
by photography in which the {ore ground and back
ground are masses of haze. It was suggested in
one of the meetings of last week, and, I believe,
there is truth in the suggestion, that lack of depth
of focus is often responsible for criticism of the
general or ayerage definition of a picture.
Depth of. focus, if there were no other considerations
involved, sets a limit to the speed to which it
is desirable to carry lens design. Just what that
limit is in cinematography I cannot definitely say
for it is a matter o{ opinion how much blurring of
the fore ground and back ground should be per*
mitted. Undoubtedly it should vary with the character
of the set. If flexibility in lighting be permitted,
a much more extensive use of the diaphragm
than is common today would improve the technique
of the cameraman.
In view of the above and other considerations into
which time will not permit us to go, it is questionable
whether better average photography would not
result from the use of lenses of somewhat less aperture
than is now employed.
In addition to the quality of the image produced
by a lens the focal length of it is an important factor
in determining the character of the picture as it
appears to observers in the theatre. All sets are
three-dimensional and the arrangement of the actors
and properties in respect of their relative distances
from the camera contributes nearly as much to the
final efiect of composition as do their separations in
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