Chp. 5: Choosing System Specifications

Chapter 5 – Choosing System Specifications


So you’ve decided to go fulldome. You’ve hopefully also decided what you want to do with your system, are prepared for the necessary investments both up front and ongoing, and you are raising the capital to convert.

Now you get to choose your fulldome system.


The fulldome marketplace is a pretty good one. There are many excellent vendors to choose from offering excellent products. The challenge for you is matching their offerings with your wants and needs. That’s going to mean more research and more decisions on your part. Don’t be afraid to talk to the vendors and ask tough questions, and make sure they’ll really meet your needs. They’re here to provide the products we want, and without our feedback and demands, they can’t do that well.


Wants and Needs


Your needs will largely depend on many of the decisions you have already made at this point. If you are building a brand-new planetarium, you can do almost anything you want—new dome, new system, new seats. If you’re converting an old installation, your decisions will be affected by what existing components you want to keep. Make sure to discuss these factors with potential vendors and with other planetarians who have made such decisions themselves in recent years.


For example, are you using an existing dome? As addressed earlier, when you shop for systems you may need to look into resurfacing to achieve optimal surface reflectivity. You may even want to consider a totally new dome anyway. The size of dome you have will affect the number of systems available to you.


Are you using an existing opto-mechanical star projector? Does it operate on an elevator? Do you want it to be controlled by the fulldome system you purchase? These factors will also affect the systems that can potentially fulfill your needs.


Do you want to keep your seating facing the same way? Do you have seat-button controls you would like to keep and utilize? An existing lighting system or plans for a new lighting system? Existing audio system or plans for a new one? Existing special effects projectors that you wish to use?

There are many variables that will affect the products you will consider, and a great deal of personal preference is going to enter into it as well. We can’t give you the answers in this booklet, but we hope to at least help you clarify the questions.




One of the big talking points as you shop for your system is going to be resolution. Resolution isn’t the be-all, end-all it’s sometimes portrayed as, but it’s important to keep in mind as you shop.


How big is your dome? Domes range from the smallest portables, 10 feet and under, up to 80 feet and greater in the largest installations. Because the planetarium industry is such a small market, fulldome equipment is generally repurposed products from the general A/V and Digital Cinema industry. Because you need a lot more pixels to cover an immersive dome screen than a flat screen, the smaller your theater is, the more projection solutions that are likely to be available to you.


Unfortunately, there are no hard and fast rules governing dome size and system resolution. Many facilities already have a preexisting dome to work with. 


There are scores of different resolutions based upon even more arrays of hardware configurations. Resolution refers to the number of pixels to be projected. The greater the number of pixels, the greater amount of projected detail will be on your dome. Instead of actually stating the number of pixels, the resolution is stated in terms of how many pixels cross the diameter of the dome. 1024 (1k), 2048(2k), 2400, 3600, and 4096 (4k) are fairly common as of this writing, but there are plenty of others available.


Pre-rendered shows are sometimes only produced in a handful of resolutions, but if your system is close, the shows should play back just find. For example, if the system you install has a projection resolution of 2400, you will still be able to play back shows created to run at a resolution of 2048 without noticing much of a difference in quality, if any.


So how much resolution do you need? In general, the more pixels on the dome, the better the quality of the projected images. Higher resolutions on smaller domes generally look great, but there are trade-offs. If the dome is also using an optomechanical projector, the surface of the dome may need to be brighter than for pre-rendered fulldome video. In that case, perceived quality of higher resolution might be lost to the extra reflected light washing out the projected images. 

Another trade-off is cost of commercial pre-rendered shows. Keep in mind that commercial pre-rendered shows are usually more expensive for domes with higher resolutions. Conventional thought is that larger diameter domes have larger budgets, although that isn't necessarily true for older facilities converting from slide projectors. 


In general, the smallest domes can get away with lower resolutions. 


1k systems, although 2k systems can look spectacular in them. Between 20 and 40 feet (maybe 45) you should begin shopping in the 2k range. 45 feet and up need to take the next step, and most would recommend they be at least 3k, although 4k is becoming predominant in domes of that size. Some installations have used 4k up to 60 or 75 feet, but for the largest domes 6k and 8k is gaining popularity. No single cinematic projector provides an 8k by 8k image (currently, anyway, but there are prospects on the horizon!), so as you climb above 2.5k, you start needing multi-channel projection arrays. 4k, currently, can be met by a pair of projectors, at minimum, while 8k installations may use between 6 and 20 projectors.


An increasingly common type of fulldome system is the truncated projection system. In a truncated system, a section at the back of the dome is left unused. Instead of projecting a circle to fill the dome, a rectangle is used. A truncated 1k system, for example, might have a 1024 horizontal resolution and a 768 vertical resolution, but the vertical component only extends from the front of the dome to 3/4ths of the way across the dome.


Truncated systems can be a great solution to maximize the coverage of your projector, although they obviously work best in unidirectional seating configurations. They may not, however, work for everyone that needs to do very thorough observational astronomy lessons that actually might involve the audience having to look behind them (but that’s not to say this challenge is unconquerable).



Brightness, Contrast and Color


As you start to figure out your needs in terms of resolution, the next area to turn your attention to will probably be the actual image quality—the brightness (the amount of light being put out by the projector), contrast (the range of difference between black, white and shades of color), and color characteristics (the richness of color, the steps between shades, etc.) of your projector. None of these factors can be looked at individually: You can get a very bright projector, but this will often come with relatively low contrast. You can also get an extremely high contrast projector, but this may come at the expense of brightness and color saturation.


One of the biggest changes going from an opto-mech is the contrast. When you have the analog contrast of an opto-mechanical projector your black is honestly, truly black—the light from the projector is being physically blocked by the metal of the projector itself, and the stars are the pure light of the illumination source. Digital projectors achieve black and white in several different ways (the glossary explains a few of these) which result in wildly varying black levels, from a fairly bright gray, to quite close to true black.


Because a high-contrast projector has a bigger difference between white and black, many find they look relatively brighter than a higher-brightness, lower-contrast projector. This may, however, be a matter of personal preference for you.


More brightness isn’t always better either, especially in the dome environment, because we have a unique concern flat screen theaters don’t have to deal with- cross-bounce. You can, of course, view an image on the screen because the light hitting the screen is bouncing back off it. But this light is not just going into the eyes of the audience, it’s going all over the room—including the opposite side of the dome. Too much light on the dome will bounce over the whole thing, making the entire thing brighter than it might be with the same projectors in a flat screen configuration. This, along with optimizing contrast for your projection solution, is where the resurfacing and repainting of your dome can be key to a high-quality final projection.


It can be hard to know just from the numbers what a given system will look like in your dome. One of the best things to do is take some trips to your neighboring planetariums and attend conferences to see the wide variety of equipment demoed in different environments to get a feel for what projection systems will work for you.


You should also keep in mind what you’ll actually be doing with your system. While brightness and contrast are very important for astronomy content, not all dome theaters are planetariums. Dome theaters built for a different puprose, such as explaining marine life, are going to have different concerns than dome theaters needing to project simulated stars. Even in a planetarium, you may need to balance a quality night sky with quality of playback of other types of content.


Projector Placement


Different systems and different projection configurations will have different mounting needs. If you’re going to have an opto-mech, they universally need to live at the center of the theater. That means you’ll have to place fulldome projectors around it—they either need to be capable of being offset to the defined front or back of the room, they need to be a multi-projector rig that projects outwards from the center, or a multi-projector rig that projects across the dome from its edges.


Even if you don’t have an opto-mechanical projector, you’ll still have to make decisions on projector placement. If you want a concentric seating arrangement, you may still want to keep the projection in the center of the room where it’s difficult to place seats. In a unidirectional seating configuration, not having equipment at the center can maximize your number of optimal seats, and you may want cove-mounted projection. In some truncated projector configurations, it’s even possible to place all of your projectors near the defined back of the theater, especially useful if you have a very low springline and unidirectional seats facing the defined front of the theater.


Multi-projection systems can be big maintenance jobs. At the dawn of the fulldome era, the CRT projectors used could require almost constant maintenance to keep them aligned. Nowadays, many advanced systems are built with greater stability to keep their alignment for long periods of time, and some even use auto-alignment systems that require only a rough alignment of the projectors, then use the power of computers to figure out the best display of the final image. More projectors, more potential for misalignment. Mounting and securing the projectors properly will minimize aligment issues, but earthquakes and nearby construction can and do rattle projectors into misalignment. If your system requires manual alignment of multiple projectors, you will want to ensure that you and your staff are well-trained for the job.


Most vendors will offer a wide variety of projection options to suit different theater configurations. Some will even work with you very closely to design a custom configuration just for your theater.


Software Control


As you’re developing an idea of what projection systems will work for you, you will also need to look at the hardware and software controlling the projection.


First, it’s important to understand that there are generally two parts to the content transmission of most planetarium systems. One part is that of the realtime components—those that are acting in real time, right now, as you are sitting at the controls!—the computer is calling up graphics, datasets, models, images and simulations from its memory as the presentation happens. The realtime components are what you would typically think of as the planetarium controls, and are also what many use to recreate their classical presentations. The other part of the system is the pre-rendered components, where the computer is merely playing back a sequence of frames or a video transport stream. Most systems will feature both of these components—the pre-rendered components differ little between them, the biggest differences being how they handle the individual frames or transport stream, and some have different levels of integration to the realtime software. The realtime components can be very different between systems, and it’s good to match the one you want with what you want to do with it.


Is teaching observational astronomy your focus, or do you do lots of other things? Are live, interactive astronomy programs with on-the-fly changes to suit the audience part of that? Or do you mainly focus on pre-recorded shows? Do you prefer to make shows yourself, or to only purchase shows from outside sources?


All of these questions can affect the software you might want to control your planetarium. If astronomy is your focus, especially live shows that you can control on-the-fly, as you might be accustomed to in controlling an opto-mech, you’ll want to make sure you get a system that has robust astronomy software and is easily controllable. If you plan to mostly do prerecorded shows, that won’t be as important.


Some systems also use realtime planetarium software that’s based on, or compatible with, commercial or free software that can be used on ordinary computers, such as Starry Night or Stellarium, which can be useful in an educational setting. Many others use proprietary programs developed specifically by a vendor.


If you want to be able to program your own non-astronomical content, or even a wide array of astronomical images—say still images or additional video sequences or 3D models, you’ll need to make sure the software will support your needs.

As you are researching and shopping, try to actually sit down at the console of a few different systems and see which programs feel most natural to you. Vendor areas at conferences and visiting neighboring planetaria are two great ways to do this. Keep in mind that a system with a simple interface may not prove robust enough for work you want to do once you get used to it, but one with too complex an interface may make it hard to do the programs you want to with ease. You’ll need to figure out what features are important for your presentations, and the level of “tech savvy” of yourself and your staff.


It is worth understanding that many features are not exclusive to a given vendor. Many vendors provide similar datasets and atlases packaged into their systems, the key differences being how you navigate through them. As above, try to find the opportunity to use the systems to get some idea of how they work to determine your preferences.


Hardware Control


Different systems also need different amounts of back-end hardware to control them. Small dome systems might only need one or two very powerful computers, while multi-projector arrays might require several racks of servers. In addition to the hardware needed for the graphics, you may also need many additional computers and components to manage audio, and for any other automation integration of lights and other effects in your theater. As mentioned in earlier chapters, larger systems also have special power and HVAC needs that will have to be accounted for.


Production hardware is another thing to keep in mind. Even if your system has a robust realtime system allowing you to create and recreate shows with relative ease, you may not want to use up premium presentation time for production. A good solution is to have another copy of the system’s software on a computer outside the dome to do this production on.


Generating pre-rendered fulldome animations can be totally different: rather than being done with the planetarium software, this is often done with traditional 3D and video production software. While it will also require powerful computers for this work to be done, the software is not specific to any given planetarium system.


What you need for production hardware, and how powerful it needs to be, will depend on what you intend to produce.




It can help, as you begin this process, to develop a clear idea of what topics you cover in a presentation. Make a list. Then make a list of what you’d like to be able to do. As you research, speak with vendors about the items on your lis,t and find the one that works best for you.


This all might sound intimidating, and it can be, but it’s worth it to make sure you end up with a product that is satisfactory. More work now will avoid headaches and difficulties down the line. It’s also good to have a clear idea ahead of time, so you can better explain to administrators and donors what your preferences are and why.