Page 28 - CinemaRecord Edition 3-2003 #41

Why Cut

An

Aperture?

by Ross King

The size and shape of the aperture
of a film projector - the opening where
the film is exposed to the light beam -
determines the dimensions of the
image. Of course it must be magnified
and focused by the projector lens on to
a cinema screen. It’s optical
engineering of a high order. Why then
was it ever necessary to alter the size of
an aperture?
In theatres such as Melbourne’s
Athenaeum or the former Metro
Bourke Street, where the projection
room was at the rear of the Upper Top: Metro Bourke Street. A high projection room created an image with a keystone
Circle, the projectors had to be tilted of this shape (above, left). If the projectors were to the left of the central axis of the
downwards at an acute angle to get the screen the distortion was this shape (above, right).
image on to the screen. This created an
Often, modifications were needed to the Care was needed when filing out an
image with splayed sides - the keystone
lens mount assembly to hold an aperture plate as one slip with the file
effect.
anamorphic lens when swing-away could mean starting all over again. For
A similar problem occurred at the
brackets were not used. this reason it was advisable to use a
Palais St Kilda where, prior to
Modification on this scale was a job small flat file with safety edge. The
Cinemascope, the projectors were
for specialists. In Melbourne the rounded corners of the standard
located in the ceiling dome bio-room.
principal engineers or firms involved in aperture and screen became too difficult
Vertical keystone was corrected or
conversions were Arthur Pyers, Bryant to file accurately, and so emerged the
disguised in one or more ways: by re-
and Hunter, Thomas McMurtrie of square cornered picture. Debate
shaping the aperture, screen masking
Austral Argo and C. Alger and Sons. continues about which is the more
and in extreme examples, such as at the
Even after this initial modification, a visually pleasing.
Athenaeum, by tilting the screen.
resourceful projectionist might do some Since the aperture plate is in a
Horizontal keystone was a problem
more reshaping of the aperture to different focal plane to that of the film,
in theatres where the projection room
improve on the result. the image will always look a bit fuzzy
was not central to the axis of the
For the projection of ‘squeeze’ around the edges. Screen masking
screen. It could also be minimised by
prints such as CinemaScope, the provides the desirable sharp edge.
reshaping an aperture.
development of the prismatic variable With modern zoom-type lenses that
The introduction of widescreen
anamorphic lens partly solved the give a near infinite number of focal
systems brought new challenges for
problem of different screen widths and lengths, the need to cut an aperture is
projectionists. Although new projectors
stage prosceniums, but in many cases it almost a thing of the past. ★
were manufactured with provision for
was still necessary to cut an aperture to
Cinemascope and its variants, many
suit the screen.
more standard projectors in use at the
time were converted for the job.
Three actual aperture ratios:
Basically, the back-plate of the film
gate had to be milled out to allow
aperture plates to be easily changed. In
most instances the aperture plate was a
small slide of either brass or copper
sheet, cut so as to slide into the milled
slot. For some projectors special
aperture plate blanks had to be
purchased from the manufacturers. Standard Academy CinemaScope with Widescreen
4:3 optical soundtrack 1.85:1
2.35:1
28 2009 CINEMARECORD