The Use of Wide-angle Slide Projection Lenses
in the Planetarium
Frank Andrews, Richard Hall and
Wayne Orchiston
Carter Observatory
PO Box 2909,
Wellington, New Zealand
Abstract The use of ultra wide-angle projection lenses in slide projectors
at the Carter Observatory's Golden Bay Planetarium is discussed.
The placement of the ultra wide-angle projectors and ways in which
they are used in conjunction with standard projectors to produce
spectacular and dynamic visual effects is outlined.
Introduction
Planetariums have an important role in science education and in
popularising astronomy (e.g. see Manning 1995, Othman 1991, Sampson
1993, Urke and Laerarhogskule 1993), and the emergence of the
thematic "feature planetarium show" is one of the highlights
in the twentieth century evolution of the planetarium. Such shows
take advantage of the stunning visual images that are now available
through the Hubble Space Telescope, and the achievements of such
astro-photographic pioneers as Dr. David Malin.
Colourful undistorted astronomical images can have major public
appeal, but their impact is often reduced in small to medium-sized
planetariums where limitations of dome size and capital budget
prohibit the use of expensive wide-angle projection systems found
in larger more affluent planetariums. Since more than 62% of all
planetariums have dome diameters of 9m or less (Petersen 1997),
this means that the majority of the world's planetariums are disadvantaged
in this way. This paper reports on the way in which this deficiency
was overcome at the Carter Observatory by using a mix of standard
slide projectors and slide projectors with relatively inexpensive
ultra wide-angle lenses.
Carter Observatory is the gazetted National Observatory of New
Zealand and was opened in 1941. It currently has four discrete
functions: research, heritage preservation, education, and public
astronomy. In 1992 a small visitor centre was added, and this
included the relocated Golden Bay Planetarium with its aging ZKP1
Zeiss projector. Since this event there has been a major expansion
of the Observatory's education and public astronomy programs (e.g.
see Leather et al. 1997; Orchiston and Andrews 1995; Orchiston
and Dodd 1996; Orchiston and Hall 1996; Orchiston et al. 1998).
This was prompted, in part, by changes to the national schools
curriculum where "astronomy" is now a compulsory segment
of the Science curriculum, within the strand "Making Sense
of Planet Earth and Beyond" (Leather et al., 1998; Science
in the New Zealand Curriculum, 1995).
The Ultra Wide-angle Lens System in the Golden Bay Planetarium
When it was first incorporated into the Carter Observatory's operations,
the Golden Bay Planetarium employed six standard Kodak carousel
projectors, with 85mm f/2.8 S-AV 1000 lenses. These projectors
were equi-spaced around the periphery of the 6-m dome (in harmony
with a concentric seating configuration), and were controlled
by a tape which also carried narration, sound effects and background
music.
Visits to IMAX theatres and planetariums in the United States,
Europe and Hong Kong, quickly brought home to the authors the
advantages of using wide-angle projection systems in a planetarium
environment. Film projection systems encountered typically used
projection lenses of 40-50mm focal length and focal ratios of
2/2.5 or f/2.8, which produced large impressive images, but such
systems were beyond the Observatory's price range and incompatible
with our dome size. The challenge was to find an affordable lens
of between 24 and 30mm focal length which would provide an acceptable
"IMAX-effect" in our small planetarium dome.
Enquiries in the United States and Germany revealed that a small
number of 26mm f/2.8 lenses had been manufactured for the Kodak
Carousel S-AV 2050 projector, which was the model used at the
Carter Observatory, but this line had been discontinued when the
projector was superseded. However, the factory in Germany had
one remaining lens, and this was purchased.
This lens was then tested in the Golden Bay Planetarium and proved
very satisfactory, although slight repositioning of the front
condenser lens was necessary in order to obtain even illumination.
In addition, only the sharpest slides, made on the finest grain
film, produced acceptable results.
The search was then on for a further lens, and a secondhand one
was eventually located in the United States.
The Observatory's first planetarium show featuring the new lenses
was titled "Venus and Mars: The Doomed Planets", and
this was launched on 1995 January 29. The concentric seating arrangement
was retained, and projectors with the two ultra wide-angle lenses
were positioned so as to project onto the east and west sides
of the dome. Meanwhile, five projectors with "standard"
lenses were distributed around the dome. Although the planetarium
show was a great improvement on earlier shows, and the large images
produced by the two new lenses were much appreciated by audiences,
the new configuration generated excessive head movement and failed
to provide an effective focus of interest for viewers.
The Observatory's next planetarium show, "Journey to the Centre of the Galaxy", was due to be launched on 1996 February 19, and in planning this a unidirectional seating arrangement was decided on. This allowed us to reposition the two slide projectors with the ultra wide-angle lenses so that they would project lap-dissolved images on the northern half of the dome. These projectors were housed in a purpose-built "projection booth", together with three standard projectors whose images could be superimposed on those produced by the ultra wide-angle lenses. The other two standard projectors were positioned on the dome perimeter 45° on either side of the main projector bank, in order to project images onto the eastern and western sides of the dome (near the edges of the ultra wide-angle frames).
By using such techniques as masking, pin registration, lap dissolve
and customised art work we were able to produce far more dynamic
effects and images than were feasible with the original projection
system.
Concluding Remarks
By using a combination of standard and ultra wide-angle 26mm f/2.8
Kodak projector lenses it has been possible to produce captivating
and visually stunning planetarium shows at the Carter Observatory
that are comparable to shows produced in larger planetariums employing
much more expensive wide-angle projection systems.
A relatively inexpensive hybrid projection system like that employed
at the Carter Observatory can be replicated with comparative ease
at any small to medium-sized planetarium facility with a limited
budget, provided the appropriate ultra wide-angle lenses can be
sourced.
Acknowledgments
We are grateful to Mark Petersen for providing relevant data on
planetariums.
References
Leather, K., Andrews, F., Hall, R., and Orchiston, W., 1998. Coping
with a new curriculum: the evolving schools program at the Carter
Observatory. In McNally, D., Norton, A., and Percy, J. (eds.).
New Trends in Astronomy Teaching. Cambridge, Cambridge
University Press (in press).
Leather, K., Andrews, F., Buckley, D., Carter, B., Hall, L., Hall,
R., Hall, S., Leather, K., Leather, N., Matla, P., Orchiston,
W., and Sule, C., 1997. Special school holiday programs at the
Carter Observatory. Publications of the Astronomical Society
of Australia 14: 283-287.
Manning, J. G., 1995. The role of planetariums in astronomy education.
Planetarian 24 (4): 5-8.
Orchiston, W., and Andrews, F., 1995. A cloudy night under the
stars: "Overnight Extravaganzas" at the Carter Observatory.
Planetarian 24 (4): 15-19.
Orchiston, W., and Dodd, R.,1996. Education and public astronomy
programs at the Carter Observatory: an overview. Publications
of the Astronomical Society of Australia 13: 165-172.
Orchiston, W., and Hall, R., 1996. Exploiting an opportunity:
the diorama displays at the Carter Observatory. Planetarian
25 (4): 10-14.
Orchiston, W., Carter, B., Dodd, R., and Hall, R., 1998. Selling
our southern skies: recent public astronomy developments at the
Carter Observatory. In McNally, D., Norton, A., and Percy, J.(eds.).
New Trends in Astronomy Teaching. Cambridge, Cambridge
University Press (in press).
Othman, M., 1991. Science education in a planetarium. Proceedings
of the Astronomical Society of Australia 9: 69-71.
Petersen, M., 1997. Tallying the world's planetarium audience.
Groton, Loch Ness Productions.
Sampson, G. E., 1993. Bringing the cosmos to the people: planetarium
education in the 1990s. Mercury Sept-Oct: 26-28.
Science in the New Zealand Curriculum. Wellington, Learning
Media (1995).
Urke, T., and Laerarhogskule, V., 1993. Research on the effects
of teaching astronomy with a planetarium. Planetarian 22
(4):19-20
Reproduced from the Planetarian, Vol. 27, #1, March
1998. Copyright 1998 International Planetarium Society. For permission
to reproduce please contact Executive Editor, Sharon Shanks.
