Chp. 1: To Be Fulldome or Not

Chapter 1 – To Go Fulldome or Not?

One of the first questions to ask yourself in this process is: Do you need and/or want to convert to fulldome video at all?

Answering this question will require asking yourself how you use your theater now, how you’ve used it in the past, and how you envision using it in the future. It will also involve examining what features of the planetarium are most important to you, and what level of sustainability and maintenance a given system will require in your dome.

There are several options to consider when looking to update equipment in your planetarium:

  • Keep the star projector, get new star projector, or use digital video projection for stars?
  • Keep the slide projectors, move to small video projectors, or use digital fulldome video for visuals?

Let’s step away from the practical concerns of budget and maintenance. What, in your wildest dreams, would you want to do with your facility in the future?



If the answer is exclusively observational astronomy, you may want to continue using an opto-mechanical star projector for your night sky simulation. No one can deny that opto-mechanical projectors produce the most vibrant, realistic and detailed starfields available. OK, sure, some of the older-model opto-mechs might not look great, and some of the newer digital sky projections get awfully close but are still not the same.

While an opto-mechanical projector’s star size (and brightness) is a fluid range of pinholes, digital projectors are restricted by the sizes of their pixels: A star can’t be smaller than a single pixel, or else it just won’t be projected at all. And while an opto-mech can smoothly move on its gears, a digital projector is changing projected images on its fixed pixels. It’s also the case that many digital projectors don’t have the same range of brightness in their stars that opto-mechs have.

Generally speaking, you’re going to get the best stars with an opto-mech, especially the newer models. You’ll also get very convenient and easy-to-manually-operate controls for your sky, planets and the basic arrays of coordinate systems necessary to teach pretty much everything covered in observational astronomy classes, and much of what is needed to do sky tours for members of the public as well.


Fulldome Video Stars

One of the leading discussions with fulldome systems since their inception has been their resolution and how that translates into the quality of the starfield. Fulldome projectors are available in a wide range of projection resolutions - from about that of a common computer monitor, to beyond the 8k resolution currently in some of the largest domes. A tremendous variety of options exist in the range in between, based on a wide range of different hardware configurations.

As you increase the size of your dome, you also increase the size of each projected pixel as well; putting a too-low resolution system in a too-large dome will make the shortcomings more apparent.

This has typically meant that digital systems’ starfields don’t look as nice as those of opto-mechs. In general, higher resolution will improve starfield quality, and this becomes necessary as dome size increases. There will be discussion of matching resolution to your dome size later on, but, in general, there are solutions that look acceptable and will continue to improve as projection technology improves and drops in price—but probably won’t match opto-mechanical quality for some time, if ever.

One advantage of fulldome video starfields is that they are not simply an Earth-centered view; instead, they are 3D simulations. Many astronomical concepts can be demonstrated by careful use of this technology as an instructional tool.

In some cases, it may be desirable to switch completely to a digital video sky. Some older star projectors make unattractive skies that are less realistic than some of the fulldome video skies. It doesn’t mean that such projectors are ineffective in teaching the night sky. It simply means that switching over to an all-digital sky might not be a bad idea, especially if your budget will not allow both a fulldome system and a new opto-mechanical projector.


Best of Both Worlds?

If your budget is sufficient, you can change to a system using both an opto-mechanical star projector and a fulldome video system. If the star projector is programmable, it can be linked to the fulldome system so that images and video from the fulldome system will align properly with the opto-mechanical projector. Then, to use the 3-dimensionality of the fulldome system, you can crossfade the realistic sky for the 3D sky.

It may also be possible to use an older star projector by hand for sky talks, and switch to the digital system for other uses. This works particularly well if your older star projector is on an elevator so that it won’t cast a shadow when showing other fulldome content.


Slide Projectors

In many domes, opto-mechs have long been supplemented by slide projectors to add additional visual illustrations. The trend in recent years has been to move away from use of slide projectors, but that doesn’t mean that you must abandon them any time soon.

Slide film and mounts, while they have had dips in availability, are still around, and probably will continue to be for some time to come. But we can probably expect continued drops in availability and increases in price as they become used only by smaller and smaller specialized markets.

Realistically, the slides themselves aren’t the problem - the projectors are. Slide projectors haven’t been manufactured since 2004, and repair shops for them are not as common as they once were. However, their lamps continue to be available, and many of the most basic repairs can be performed by anyone.

Slide projectors aren’t necessarily the weak link they’re portrayed as by some, and especially in the short term, there’s been a flood of used slide projectors on the market from planetariums that have converted and no longer need them. Staying a “classical” planetarium is still a viable option.


3-Screen Video

That said, slides aren’t always the best or most adaptable display solution, and for years many have supplemented them with video projection, which, of course, can also be used to display still images. In fact, even facilities with fulldome projection systems benefit from having a dedicated LCD or DLP projector for presentations and talks run from laptops.

The use of video in our domes has led to a not-uncommon low-budget method for upgrading opto-mechanical planetaria: a layout called 3-screen video.

3-screen video is exactly what it sounds like: The star projector is supplemented by three video projectors which provide all the auxiliary images for your presentation. 3-screen video can be used for fairly robust presentations, and can be a great way to enhance an older theater if you don’t need fulldome video.

Going to 3-screen video, and maybe keeping a few slide projectors, will allow most opto-mechanical theaters to continue presenting all the programming they’ve always done, and even enhance some presentations.



Content – Shows and Show Kits

And shows—that’s another topic to think about. Do you run prerecorded shows in your theater? Do you produce them in-house, or purchase them from other theaters or vendors that specialize in show creation?

The availability of shows can be another area of concern for classical theaters. While many classical shows are still available for theaters, the producers in the industry have been moving to fulldome video. Even though shows will continue to be available for classical theaters, an increasing number will probably be conversions of fulldome productions that may not offer the complete experience intended by the program. If you present prerecorded shows, even if you choose not to adopt fulldome video, it may still be dictating what programs are available to you.

If you produce your own content in-house, changing to fulldome might require significant changes to your production workflow. But the flexibility of the medium may allow you creativity and freedom never before possible.



          Lastly, we should also look at the expenses involved in fulldome video. It’s not a cheap endeavor, and it has many maintenance costs associated with it that we’ll look at in later chapters. Even if you want the versatility and capability of fulldome, if you can’t justify the ongoing maintenance and upgrade costs, it’s probably a good idea to stick with analog equipment. Non-digital opto-mechs and other classical components tend to be less fussy than computer components.



It’s not a simple, straightforward question. Should you switch to fulldome? Take some time, think long and hard about how you use your theater and what you might want to do with it. What is your vision of what a planetarium could and should be? What technology will actually help you meet that vision? There are many great qualities to fulldome video, and there are many great qualities to classical theaters—and there can be downsides to both. Both can be used to reach your audience and teach and inspire the next generation, but which will best enable you to do it? That’s not a question this booklet, or anyone else, can answer for you.