Mirrors


This month I am not going to talk about electronics. Rather, I
decided to relate experiences using mirrors used to extend
projection capabilities in production situations. Mirrors made of
both glass and mylar can be put to good use in order to solve a
number of production challenges involving projections and general
lighting. Here I am using examples where limited projection
distance is a significant constraint to the size of image that can
be produced.

Ever had a situation where a large projection was needed only to
find that there was not enough projection distance to achieve the
image size desired or that the position in which the projector was
to be placed created large keystone distortions? Didn't have,
couldn't afford the necessary lens? An ordinary bureau size mirror
can allow you to often double the effective projection distance by
allowing the projector to be placed at the base or above the
projection surface facing downstage. The projector to mirror
distance should be the maximum that allows the projection image to
fill the mirror. Of course often a piece of scenery is necessary to
mask the mirror. The mirror is then placed at a distance that will
fill the projection surface or the maximum downstage distance while
maintaining the projector to mirror distance. Careful positioning
of the projector and mirror can also be effective in cancelling all
or most of the keystone effects of projecting at an angle. The
larger the mirror, The more distance possible between the projector
and the mirror and, therefore, the greater the magnification that
can be achieved. Glass mirrors in my experience work best for this
setup due to their inherent rigidity. Mylar mirrors have to be
mounted in such a way as to be perfectly flat and rigid. There will
be some loss of image brightness because the mirror's reflection is
not 100 per cent but all in all this procedure works well.

A relatively small mirror can be utilized as an inexpensive 90
degree lens to turn a projection to a right angle horizontally or
vertically. This technique is particularly useful if the projector
must be overhead and the projection is to be straight down on the
floor. Again any possible distance between the projector and
mirror, assuming the mirror is large enough, is added to the
projection distance.

The same rationale applied to lighting instruments, although some
consideration must be given to the projected heat of a lighting
fixture. The heat consideration is generally negligible for
carousel type projectors. Here precise clarity is not generally an
issue so unmounted sheets of mirror plexiglas can suffice so long
as they do not warp sufficiently to produce distortion patterns.
Using a 4x4 foot sheet of mirrored plexiglas is extremely useful
when a large object such as a moon shape must be silhouetted or
illuminated from the rear but the distance to the cyc wall is only
three or four feet. The additional throw distance achieved has the
additional effect of de-emphasizing the hot spot of the instrument.
Multiple lighting fixtures can be mounted on a tree to the side
with focus on the mirror serving to allow them to seem to have the
same origin, i.e., the center of the object being illuminated.

I put this mirror reflection technique to a particularly
interesting use a few years ago. For a scene in Tennessee Williams'
"The Glass Menagerie", candlelight was required that emanated from
a candle placed on the floor. I didn't want to place lighting
fixtures on the floor in front of the set as they would have been
obtrusive to the audience. The candle light needed to cover a large
stage area over a wide arc downstage to upstage. The initial idea
was to build frames to hold mirror plexiglas bent into a 90 degree
arc. This produced the typical psychedelic distortion patterns when
lights were projected onto the mirrors from above. The solution to
this difficulty came in covering the mirror with frost or silk
diffusion media. Interestingly, it didn't matter what type or
density of diffusion was used. The instruments used in this case
were a series of 3 1/2 inch ellipsoidals sharply focused onto the
mirrors(We only have a 12 foot ceiling). Slightly different values
of the warm color for the candlelight were placed in each of the
lighting fixtures. The result was a soft even wash of light seeming
to emanate from the area of the candle. The effect was enhanced by
using several instruments and pulsing the intensities. In this way,
the romantic effect of the flickering candle was created. 

A last practical use is to use strategically placed small mirrors
to allow a stagehand to see events not normally in his field of
view. In all cases, this and all previous examples, care must be
taken that extraneous lights do not strike the mirrors causing
unwanted reflections.

In an upcoming production, I am considering the use of flat mirror
plexiglas, placed at an angle on the front of the stage, in an
attempt to produce the clarity of a lighting fixture placed in the
position of a footlight without the distraction of the lighting
fixtures having to be placed in view of the audience.