Digistar planetarium technology question?

hsap...@clark.net

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Jan 2, 1996, 3:00:00 AM1/2/96

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Manolis Zoulias (mzou...@hol.gr) wrote:

: surfing the web I came along Digistar's www site and saw that it uses , for
: projecting stars , constellations etc. a CRT , the light from which is
: projected on the dome through a fish-eye lens.

I recently had the chance to visit a Digistar-equipped star theatre
(Philadelphia) and was actually less than impressed with the quality of
the starfield that the projector rendered on the dome. The stars were
quite fuzzy and had an alarming tendency to jump about within their
constellations as the sky was in motion! Is this perhaps because Philly
has an early model of the projector or are new Digistars also prone to
this phenomenon?

The console operator didn't have much to say on this subject.

One thing which *was* spectacular about the Digistar, though, was its
ability to project animated computer diagrams over the entire dome. What
I wouldn't have given for that capability when I was in the business...

--
| $ |
|---. ,---. ,---. ,---. . ,---. ,---. ,---. | "Most people would sooner die
| | `---. ,---| | | | |---' | | `---. | than think; in fact, they do."
` ' `---' `---^ |---' ` `---' ` ' `---' | -- Bertrand Russell
| hsap...@clark.net |

Paul Schlyter

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Jan 3, 1996, 3:00:00 AM1/3/96

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In article <4bhvn1$1...@newsflash.hol.gr>,
Manolis Zoulias <mzou...@hol.gr> wrote:

> surfing the web I came along Digistar's www site and saw that it uses , for

> projecting stars, constellations etc. a CRT, the light from which is

> projected on the dome through a fish-eye lens.
>

> Since no planetarium using this modern technology is installed here in
> Greece, to check it out, I was wondering if anyone knows about the
> technology of such CRTs, since producing enough light for all these stars
> and effects on a 12 to 25 meter dome, requires a rather large amount of
> light, that normal CRTs have not the ability to produce (not even close).

Be happy that your country has no DigiStar planetarium.

A few years ago, the very first large planetarium in Sweden, "The
OmniTheatre", was opened in Stockholm. It uses the DigiStar
projector, and the image quality is NOT GOOD! The image is faint,
unsharp, and of course in black-and-white only. The DigiStar may
offer some flexibility, however the image quality is far inferior to
the image produced by a traditional Zeiss planetarium. I almost
never visit the OmniTheatre here in Stockholm, where I live --
instead I try to visit Zeiss planetaria in other cities of the world,
whenever I have the opportunity.

--
----------------------------------------------------------------
Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF)
Nybrogatan 75 A, S-114 40 Stockholm, SWEDEN
e-mail: pau...@saaf.se p...@home.ausys.se

John A. Schroer IV

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Jan 4, 1996, 3:00:00 AM1/4/96

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As a planetarian that has used both traditional (Minolta) and modern
(Digistar) planetariums, I feel that I can fairly judge the pros and cons
of both technologies.

Well, here goes..............

Traditional planetarium such as Zeiss and Minolta use brilliant light
sources to illuminate star plates with holes for the stars, and colored
glass to give stars their proper color. The light then passes through
several lenses, and is projected onto the dome.

Digistar utilized a computer to store the pertinent information, uploads
the required information to the Digistar graphic processor, which draws the
image, and then sends it out the the Digitstar projector. The projector
consists of a 7 inch (17.75 CM) cathode rat tube (CRT), power supplies,
deflector amps which guide the projected electrons and create the image.
The light from the CRT is sent through a large fish eye lens onto the dome.

That's how both work. Now for the pros and cons.

1. Digistar images are monochromatic (a single color, light green)
Traditional projectors have proper star colors.

2. Digistar images are not as sharp as traditional, since it is a video
projection system.

3. HOWEVER, only Digistar can show an audience the effect of proper motion,
traverse a sphere of the Earth's neighborhood in the Milky Way
approximately 900 light years in radius, bring up constellation pictures
for all 88, draw constellation boundaries, Right Accession and Declination
grids, celestial coordinates, and other effects that traditional
planetariums can not touch.

In my humble opinion, Digistar has a place as an excellent educational tool
for teaching astronomy. But you won't find me using Digistar only. I need
to see the real sky once and a while.

BY THE WAY.....traditional planetariums such as the Zeiss can run up to 2
million dollars (US), while a Digistar comes in at five to six hundred
thousand dollars (US).

I hope that you find this information enlightening.

Also, the London, England Planetarium just converted over to
Digistar...Digistar II that it. The NEW Digistar II uses a mini-tower Sun
workstation and has sharper stars and more memory.

Check it out!!!

--

John A. Schroer IV
Assistant Curator of Astronomy
Dayton Museum of Natural History
2600 DeWeese Parkway
Dayton, Ohio 45414
(513) 275-7431 ext. 36

Chuck Wilcox

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Jan 5, 1996, 3:00:00 AM1/5/96

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In newsgroup sci.astro.planetarium,
jschr...@usa.pipeline.com(John A. Schroer IV) wrote:

>Traditional planetarium such as Zeiss and Minolta use >holes for the stars, and colored glass to give stars their >proper color. The light then passes through several

>lenses, and is projected onto the dome.

One other detail about the Zeiss, at least the Model VI we
have here in Boston, MA (Charles Hayden Planetarium):

The brightest stars (to mag. +1.0) each have dedicated
single-shot projectors mounted on the collars of each of the
large star spheres, outboard of the planet cages. This
allows for a much greater range of magnitudes than is
possible with a system that relies only on the size of the
holes punched in the star plates, or the intensity of the
CRT beam. This, IMHO, is what sets the realism of the Zeiss
sky apart from that of Digistar.

Of course, systems that use fiber-optic light guides offer
an even more tremendous brightness range combined with an
extremely small star image size on the dome. The realism
thereby produced is truly stunning.

Prior to the installation of our Zeiss in 1970, we had a
custom-built projector constructed by Bill and Frank Korkosz
(you may have heard of them) of Springfield, Massachusetts.
For a purely optical system it ranked among the finest (more
stars than even our Zeiss' 8900 stars, smaller images, and
even a Uranus planet projector!)

Chuck Wilcox
Charles Hayden Planetarium
Museum of Science, Boston
wil...@a1.mos.org

Jack Dunn

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Jan 6, 1996, 3:00:00 AM1/6/96

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Paul Schlyter (pau...@electra.saaf.se) wrote:
: In article <4bhvn1$1...@newsflash.hol.gr>,
: Manolis Zoulias <mzou...@hol.gr> wrote:

Unfortunately NO Planetarium projector is as good as the real sky.
That goes for contrast, color, and all visual elements. The debate about star
projectors has ranged for years and started long before Digistar. I
believe that it ignores a fundamental concept of the planetarium. We
have to ask ourselves what the facility is trying to do. We can't
outdo God, the Cosmic AC or whatever in reproducing the sky. The
Planetarium is merely a tool. If I'm trying to teach the
constellations or explain the motions of the Earth, explore the
mysteries of the planets, etc. - it all depends on how I use what
tools I have. I've seen people teach more astronomy in a portable
planetarium than in a huge theater with a Zeiss. That doesn't mean
the inflatable's sky is truer to the real thing. What it means is
that someone is doing a better job of teaching and that's a human
question not a machine question. And this is where our energy should
be spent. You can do it with a Zeiss, a Digistar, or any other
projector if you have the talent and the motivation.

The knowledge of the heavens for the average citizen is abysmal. The
knowledge of the average elementary or secondary school teacher when
it comes to astronomy is worse than ever and it affects what their
students know. These are our real problems today.

I do not mean that we should select flash over substance. But there
are real principles which computer graphics can demonstrate that a
fixed projector can't touch. Maybe we'll address them with Digistar
or video or laser projected via something like Omniscan. But they are
things worth teaching non the less. And what about all the great new
images and information provided by the Hubble Space Telescope or any
of the space probes of recent years. There's a whole body of
information in astronomy to teach and it doesn't depend what the stars
look like on a certain star projector.

If your thought is that the planetarium is merely a curiosity to be
visited once in a lifetime. And if you don't care about learning
anything - all you want is to "experience" a sky, then go find an old
projector in a big dome and stare at it. You'll be impressed.
But so what?

We need more people committed to reaching the people of this world
with the exciting discoveries and mysteries of astronomy. That
commitment - rather than worrying about star projectors and misguided
nostalga is what is important.

But then, I'm just a lowly planetarium person. I'll take what ever I
can get be it a Zeiss, a Digistar, a Spitz, a Goto, a Minolta, or an
Omniscan. Hey, wait maybe I should ask for one of each.

But none of them looks like the sky from the a real dark-sky site.
Guess what? It doesn't matter.

--
Jack Dunn - Mueller Planetarium-UNL
On the Web at http://www.4w.com/mueller
If you have a laser projector, join ILDA

Paul Schlyter

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Jan 8, 1996, 3:00:00 AM1/8/96

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In article <4cmsd0$9...@crcnis3.unl.edu>,

Jack Dunn <jd...@unlinfo.unl.edu> wrote:

> Paul Schlyter (pau...@electra.saaf.se) wrote:
>: In article <4bhvn1$1...@newsflash.hol.gr>,
>: Manolis Zoulias <mzou...@hol.gr> wrote:
>
>:> surfing the web I came along Digistar's www site and saw that it
>:> uses , for
>:> projecting stars, constellations etc. a CRT, the light from which is
>:> projected on the dome through a fish-eye lens.
>:>
>:> Since no planetarium using this modern technology is installed here in
>:> Greece, to check it out, I was wondering if anyone knows about the
>:> technology of such CRTs, since producing enough light for all these stars
>:> and effects on a 12 to 25 meter dome, requires a rather large amount of
>:> light, that normal CRTs have not the ability to produce (not even close).
>
>: Be happy that your country has no DigiStar planetarium.
>
>: A few years ago, the very first large planetarium in Sweden, "The
>: OmniTheatre", was opened in Stockholm. It uses the DigiStar
>: projector, and the image quality is NOT GOOD! The image is faint,
>: unsharp, and of course in black-and-white only. The DigiStar may
>: offer some flexibility, however the image quality is far inferior to
>: the image produced by a traditional Zeiss planetarium. I almost
>: never visit the OmniTheatre here in Stockholm, where I live --
>: instead I try to visit Zeiss planetaria in other cities of the world,
>: whenever I have the opportunity.
>

> Unfortunately NO Planetarium projector is as good as the real sky.

I know -- but some are better than others. The DigiStar is a clear
step backwards in sky realism, compared to the better of the earlier
projectors.

Above you really say that planetarium shows are directed to people
whose knowledge about astronomy is abysmal. It's of course ok that
the planetarium tries to target its shows to as large an audience as
possible, however this causes problems for visitors who doesn't fit
this category, i.e. for people who knows something about astronomy.
Perhaps we'll just have to face the fact that planetariums today
aren't meant for such people?

> But then, I'm just a lowly planetarium person. I'll take what ever I
> can get be it a Zeiss, a Digistar, a Spitz, a Goto, a Minolta, or an
> Omniscan. Hey, wait maybe I should ask for one of each.
>
> But none of them looks like the sky from the a real dark-sky site.
> Guess what? It doesn't matter.

That depends on what you want!

If all you want is some entertainment, either by some "laserium" show
or by some planetarium show with lots of flashy pictures presenting
the latest fantastic facts from astronomy, it of course doesn't
matter.

Also, if all you want is an audience who don't know the sky, and you're
not having any ambition to try to learn them, then it doesn't matter
either.

But if so, is the planetarium projector needed at all? If the
planetarium sky need not look like the real sky, why not simply
replace it with a projector projecting a collection of bright dots,
randomly, on the dome? The average person won't notice the
difference, and the planetarium instructor can have a good show anyway,
right?

--------------

One thing I tried to use planetariums for earlier, during many years,
was to learn the constellations of the southern sky: I would check a
star map carefully before the show, and then try to find Centaurus,
Vela, and all those southern constellations from whatever glimpses of
the southern sky that particular planetarium show would allow
(interestingly, "laserium" show were often better for this, because
quite often the planetarium projector were then left to move around
more or less randomly, presenting the southern sky as often as the
northern sky. Normal planetarium shows were far too often displaying
only the northern sky + only small parts of the southern sky, as
directed by the programme). Later, when I saw these constellations
for the first time on the real sky, I recognized them much easier,
because I had "seen" them before. Even today I try to do this,
whenever I have the chance to visit a planetarium with Zeiss-like
quality of the sky, since I do enjoy watching constellations, and I
don't get the opportunity to see the far southern skies that often.

I've also tried this on a DigiStar planetarium show (here in
Stockholm), but it's MUCH HARDER to recognize the constellations when
the brigtnesses of the "stars" aren't reproduced very well.

Isn't this what planetariums really were meant to be used for: to
learn your way around the sky? Of course I know that most people
aren't interested in this. Perhaps I'm also committing a "cardinal
sin" when I want to use the planetarium for my own purposes instead
of just following the planetarium show as presented?

You suggested:

# If your thought is that the planetarium is merely a curiosity to be
# visited once in a lifetime. And if you don't care about learning
# anything - all you want is to "experience" a sky, then go find an old
# projector in a big dome and stare at it. You'll be impressed.
# But so what?

an that's NOT what I want to get out of a planetarium show! First,
I'm not merely getting "impressed" -- I'm trying to find my way
around the artificial sky, as the show allows. Second, I'm not
visiting just once -- a Zeiss planetarium I'd like to revisit
numerous times. During a one-year stay in New York City in 1977,
I visited the Hayden Planetarium there about 10 times. Here in
Stockholm I've visited the "Omnitheatre" perhaps 4 times, and only
2 of these visits were to planetarium shows, the others were
OmniMax film shows (which indeed are impressive, however they don't
even use the Digistar projector....).

And I guess it's time to try to get an up-to-date list of the
planetaria that still uzes Zeiss projectors. London recently
switched to DigiStar, so I need not visit there anymore. What about
Copenhagen? Munich? Anyone who knows where such a list can be found?

lhsa...@garnet.berkeley.edu

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Jan 9, 1996, 3:00:00 AM1/9/96

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From am...@gemini.oscs.montana.edu Mon Jan 8 17:26:00 1996
Subject: Digistar

Friends:

Concerning the "Great Planetarium Debate," I'd like to offer one tiny
nugget of wisdom I've picked up after 20 years in the business and after
working for years with Digistar, two kinds of Zeiss projectors, a Spitz
A3P, a Starlab, and being familiar with other models and machines: there
is no perfect planetarium projector.

Every model has its strengths and weaknesses. One of the weaknesses of
Digistar is its (current) inability to project as crisp and sharp a
starfield as analog projectors and fiber-optics models. One of its
strengths is its ability to present honest-to-God three dimensional
astronomy as a part of its computer graphics capabilities which can educate
every bit as much as entertain. It looks different in different theaters:
on large domes with relatively low reflectivity, Digistar is dimmer and
fuzzier; on smaller domes with greater reflectivity, the images are
brighter and sharper. And Digistar's manufacturer continues to make
improvements--even as do the other planetarium manufacturers.

Any choice of planetarium projector requires compromise; those who buy and
use them must determine which strengths they wish to take advantage of and
which weaknesses they're willing to live with.

Different people come to different conclusions. And you know what? That's
okay.

Regards,

Jim Manning
Museum of the Rockies
Bozeman, Montana USA

*********************************************************
* James G. Manning - Director | /\ MOR |
* Taylor Planetarium | / \ /\ |
* Museum of the Rockies | / / /\ |
* Bozeman, MT 59717 | / / / \ |
* am...@gemini.oscs.montana.edu |/____/__/____\|
*********************************************************

Kevin Conod

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Jan 9, 1996, 3:00:00 AM1/9/96

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> Above you really say that planetarium shows are directed to people
> whose knowledge about astronomy is abysmal. It's of course ok that
> the planetarium tries to target its shows to as large an audience as
> possible, however this causes problems for visitors who doesn't fit
> this category, i.e. for people who knows something about astronomy.
> Perhaps we'll just have to face the fact that planetariums today
> aren't meant for such people?

That's exactly right! Planetariums ARE directed to those people. And
rightfully so. Who the hell wants to preach to the choir?!!

> Isn't this what planetariums really were meant to be used for: to
> learn your way around the sky?

Yes, and they still are...but not EVERY single show we present is about the
constellations. Planetariums have grown to be more than that - we present the
latest from the space program and the latest astronomical discoveries as well.

> Of course I know that most people
> aren't interested in this.

On the contrary, it is still the most popular topic under our domes.

Kevin Conod | kdc...@delphi.com
Astronomer, |
Dreyfuss Planetarium | Check out our Web Page:
Newark Museum, NJ | http://www.rutgers.edu/newark/MUSEUM/dreyfuss.html

Christopher A. Seale

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Jan 9, 1996, 3:00:00 AM1/9/96

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>From am...@gemini.oscs.montana.edu Mon Jan 8 17:26:00 1996
>Subject: Digistar

>
>Any choice of planetarium projector requires compromise; those who buy and
>use them must determine which strengths they wish to take advantage of and
>which weaknesses they're willing to live with.
>
>Different people come to different conclusions. And you know what? That's
>okay.
>
>
>Regards,
>
>Jim Manning
>Museum of the Rockies
>Bozeman, Montana USA

I've been waiting for this debate to resurface on this newsgroup... in my
opinion, this is more or less a variation on recent perennial debates such
as "Which is better: live or canned shows?" and "Which is better: large
or smaller theaters?"

A couple of others here have already raised this point, but I think it's
worth restating: "There's more than one way to be a planetarium." I've
had the fortune of working in several different theaters in several
different cities, with very different equipment and operating styles.
I've also been fortunate to see them all get the job done in their
different ways.

Digistar is not, by any wild stretch of the imagination, a really good
simulation of the night sky. It is, on the other hand, a *really* good
educational tool, if it's users choose to employ it as such.

hey, but Zeiss is cool too.

--
ch...@laserfantasy.com Christopher A. "mothboy" Seale, signing off.
Performing live for Laser Fantasy at The Children's Museum of
Indianapolis..."There's a flame around here, I'm sure of it!"

Paul Schlyter

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Jan 10, 1996, 3:00:00 AM1/10/96

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In article <4cu2cg$5...@agate.berkeley.edu>,

<lhsa...@garnet.berkeley.edu> wrote:

> Every model has its strengths and weaknesses. One of the weaknesses of
> Digistar is its (current) inability to project as crisp and sharp a
> starfield as analog projectors and fiber-optics models. One of its
> strengths is its ability to present honest-to-God three dimensional
> astronomy as a part of its computer graphics capabilities which can educate
> every bit as much as entertain.

How does that work?

I suppose the Digistar cannot project holograms on the dome. What
seems to remain is then using twin Digistar projectors, with either
red+green filters, or polarizing filters + corresponding glasses on
each person in the audience. But wouldn't that make the already quite
dim Digistar image still dimmer?

Mark Petersen

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Jan 10, 1996, 3:00:00 AM1/10/96

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Weighing in on this perennial debate:

>> Isn't this what planetariums really were meant to be used for: to
>> learn your way around the sky?

>Yes, and they still are...but not EVERY single show we present is about the

>constellations. Planetariums have grown to be more than that - we present the
>latest from the space program and the latest astronomical discoveries as well.

No one person can say "what planetariums really were meant to be used
for", since they can and are used for many purposes.

And I have to laugh at the notion of someone going to a laser show to see
Southern hemisphere stars! "But the dang laser keeps blocking the view..."

>> Mark

--
/-------------------------------------------------------------------------\
| Mark C. Petersen Loch Ness Productions 7225...@compuserve.com |
| ma...@lochness.com http://www.lochness.com mar...@scicom.alphacdc.com |
\--------------------------**-GEODESIUM-**--------------------------------/

John A. Schroer IV

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Jan 10, 1996, 3:00:00 AM1/10/96

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In the final analysis, it is how you use the star projector, and not its
particular pros and cons, that determine if our field can turn around
the incredible lack of knowledge and apathetic view of astronomy.
Thanks, Jack, for reminding all of us on what is really important!!!