Sky and Telescope - November 2018 - 33

three times more telescope time than what was required for a
monochrome image). As this was unachievable with the limited telescope time available, Malin decided to use as much
archival material as possible. This approach took advantage
of monochrome plates made for photometric work using the
standard astronomical B, V, and R photometric system to
create a realistic RGB color image. The decision enabled the
acquisition of plates to fit into the normal routine of the telescopes. This meant that plates obtained for variable-star photometry or supernova studies could also be used to produce
color images. As a bonus, there were already many previously
exposed B and V plates; only an additional R-band plate was
required to complete a color composite. These could often be
obtained in twilight at both ends of the night.
The original plates were obtained using Kodak spectroscopic emulsions and Schott glass filters. Going forward, all
the plate batches were tested to characterize their long-exposure sensitivity to establish the best exposure time for each
color band, typically between 40 and 60 minutes for each
type of hypersensitized photographic emulsion.
After some time experimenting with darkroom procedures,
Malin established a technique to
make positive copies of the plates by
controlling contrast, density, and
dynamic range during the chemical
u GALACTIC FIREWORKS Because
many B and V plates were recorded for
spectroscopic studies, the R (red) plates
needed to complete the color set were
often recorded several months or even
years later. The B and V exposures of this
photograph of Centaurus A were recorded
shortly after the discovery of a supernova
in its dust lane, but poor weather delayed
the exposure of the red plate until long
after the star had faded, resulting in the
odd blue-green star.

processing. Then, the three copies were overlaid sequentially
by projection on color-sensitive photographic paper using an
enlarger with red, green, and blue filters for the appropriate
exposures. A simple frame permitted aligning the projections.
The process could be performed in less than 15 minutes.
Malin successfully applied Maxwell's tricolor composition
technique using monochrome plates from one of the best
astronomical telescopes in the Southern Hemisphere. And he
did it more than 100 years after Maxwell presented his theory
about color photography.
The technique allowed Malin to create a number of images
from the late '70s through the mid-'80s when he had access
to the AAT and plates from UKST. Nebulae and galaxies were
shown in their natural colors, and a chromatic explosion
began appearing in magazines. Color images also made it possible to visualize some astrophysical processes for the first time.
The photographs were not only useful for science, but
also in promoting the beauty of astronomy. Color psychology
did its work, and suddenly, everybody wanted color photographs of the universe. People unconnected to astronomy
felt attracted to those images, combining familiar color and
distant splendor.
All this extraordinary dynamism
of color developed in the analogue
processes of chemical photography
in the late '70s, converging just
before an emerging technology rose
to the forefront. The charge-coupled
device (CCD) and computerized
image processing were on the horizon, which together would change
photography and astronomy forever.
Chemical processing, glass plates,
and a lot of hypersensitization gear
were leaving observatories as the
digital age ushered in a new order
where color images are much easier
to obtain and process.
However, some things haven't
changed.
Tricolor imaging through
t COLOR EXPLOSION
red,
green,
and blue filters is still the
Recorded over several
months in 1979 with the
preferred system for recording the
UKST, this deep image of
best deep-sky images by amateur
M20 (top), M8 (right), and
astrophotographers and professional
NGC 6559 (left) was the
astronomers alike.
best natural color photo of
Malin's images played a big part
the field at the time.
in popularizing astronomy in the
late '70s and '80s thanks to the enigmatic attraction of color
over all of us. This is one major legacy of his work.

¢ ANTONIO PEÑA is an engineer working in the European
aerospace industry. In his free time, he images the night sky
with a Ritchey-Chrétien telescope and DSLR camera with
lenses. He is grateful to Dr. Malin for his help and support while
researching this article.
sk yandtelescope.com * N OV E M B E R 2 018

33


http://www.skyandtelescope.com

Sky and Telescope - November 2018

Table of Contents for the Digital Edition of Sky and Telescope - November 2018

Contents
Sky and Telescope - November 2018 - Cover1
Sky and Telescope - November 2018 - Cover2
Sky and Telescope - November 2018 - 1
Sky and Telescope - November 2018 - Contents
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