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Frequently Asked QuestionsBelow are answers to common or important questions.
BasicProjectionProduct ComparisonsSoftware FeaturesInflatable DomesGeneralPurchasingBasicWhat does it mean that your systems are digital? Why is that important?A digital planetarium system is a computer based system using digital projection, as opposed to an analog type pin-hole or lens based projection system. It is a huge difference, because a computer based system is so much more flexible than an analog system. Think of the difference between a computer and a slide projector and you start to see the power of a digital system. In a digital system, the projected image is made up of individual pixels. Because the dome is covered by an array of pixels rather than a fixed set of holes or lenses, anything can be projected: views from other planets, videos, images, other applications. Analog systems can often produce smaller stars and higher contrast ratios, but without any of the flexibility of digital systems. So unless your goal is to try to match the night sky as closely as possible, and nothing more, you really need a digital planetarium system. For more detail, see How does a Digitarium system compare to an analog Starlab projector?. I want to build a planetarium. Where should I start?
ProjectionCan the same projector be used in domes of different sizes?Yes. The lens has almost infinite depth of field, which means there are no focus issues due to differing dome sizes, although brightness is an issue:What is the maximum dome size recommended for a Digitarium system?It depends on the Digitarium model. Details are on this page. Dual lamp models are brighter and can work in larger domes. With a dual lamp system in a smaller dome you can either have brigther projection, or use just one lamp and keep the other on standby for automatic failover. Your dome surface and projection content will also play a role in determining what model is acceptable. What is the minimum dome size for a Digitarium system?Approximately 1 foot/30 cm in diameter.Will stars be larger on a larger dome?At the surface of the dome each pixel will be physically larger on a larger dome. However, angular pixel dimensions do not change with dome size, so on average pixels do not appear larger to an audience. Someone sitting next to the side of the dome will obviously see larger pixels nearby than on the opposite side of the dome due to their perspective. Someone seated near the middle would not notice any difference other than brightness between domes of different sizes.How high a contrast ratio do I need?In a planetarium, it is somewhat distracting if the dark areas of a starfield are a dark gray rather than a full black. How black the dark areas appear depends on a number of factors, including the contrast ratio of your projector. The contrast ratio of a projector is the ratio of the luminance of a white projection compared to a black projection. Digital projectors usually have much lower contrast ratios than analog projectors, which is just inherent to the technology differences. The higher the contrast ratio, the darker the black areas are compared to the bright areas. With a low contrast ratio, blacks appear as dark gray rather than true black. A number of LCD digital planetarium systems have a contrast ratio of 400:1. The Digitarium Alpha 2 has a measured contrast ratio of approximately 900:1 in low contrast mode. The Digitarium Alpha 2+ has a measured contrast ratio of 1200:1. The Digitarium Gamma has a measured minimum contrast ratio of 2100:1 in dual lamp mode. When comparing systems, ask whether the contrast ratio quoted was actually measured with the lens you would be using on the projector. Also be aware that there is a tradeoff between projection brightness and contrast so you usually can't get the highest contrast and highest brightness at the same time. Usually a digital projection system is used with a light gray dome surface to enhance the black level. The light grey is less reflective than a traditional white dome, and thus darkens the projection and reduces the luminance of the black areas. Since the black level is more noticeable than the actual contrast ratio, this tends to be a good solution. The gray color further reduces cross-reflection on the dome, when a bright image on one side of the dome reflects across the dome and washes out darker areas. Another option to adjust the black level is just to turn the projector lamp down to low. As you would expect, the dome size also will affect the black level seen by the audience. In summary, it is the black level luminance perceived by the audience that is what you should focus on, although selecting an acceptable level is subjective. The projector contrast ratio affects the black level, but there may be more cost effective ways to achieve the same effect with a lower contrast system. If I project a rectangular image, movie, or PowerPoint through your projector, what will it look like?Fisheye projectors will introduce a large amount of distortion if you project a standard perspective image or application at full projector resolution. By distortion we mean that the projected image is deformed from its natural shape. In a Digitarium system a central circular area of the video source is projected onto the dome. The outer rim of the circle is projected at the horizon, and the center of the image is the zenith (top of the dome). This is called a polar projection. If you projected a PowerPoint slide full of text at full projector resolution, you would see your text cover the entire dome, but half of it would be upside down as it wraps past the zenith. So what we recommend is to save your slides as images at about half your dome diameter resolution and flip through these from a USB thumb drive using the built in media browser. You can easily go back and forth between a slide and the sky for demonstrating celestial phenomena. With common images the human mind copes pretty well with the distortion. Lower resolution or smaller content works great as it will appear more or less undistorted at the zenith. Fulldome applications and content are designed to immerse the audience in a 3d environment. It is not possible to add this extra dimension to regular perspective content after the fact. So while it's easy to project over the entire dome, unless you have content or an application that supports polar projection, your content will definitely be distorted to some extent. This may or may not be a problem. Is your lens distortion free?(Be sure to read the above question and answer also.)As an affordability tradeoff, our lens varies slightly from an ideal linear polar distortion. In most cases this will not be noticeable. The following two images illustrate this slight distortion (in this case for the Digitarium Alpha 2). If the first image was projected through the projector over the whole dome, it would end up looking like we had projected the second image through an ideal distortion lens.
  Pacific Science Center, Seattle As you can see, the distortion is subtle. Your audience will generally experience a lot more distortion simply due to their perspective away from the center of the dome (where distortion due to perspective is zero). Our planetarium software uses distortion correction software algorithms, so you will not see any lens distortion using the planetarium features. The slight variation in pixel sizes across the dome is not noticeable. If you need exact distortion for a custom fulldome application we can supply distortion functions. Where do I put my projector in a fixed dome?Our projector is designed to be placed in the center of the dome, whether fixed or portable. Here are diagrams explaining how to calculate projector placement:
Product ComparisonsWhy is your system so expensive?
Why is your system so inexpensive?
Aren't there patent issues with fisheye projectors?Yes. There is a very broad patent covering digital projection through a fisheye lens: US patent 5,762,413. We felt the patent license fees were unbearably high, so we were forced to design our own optics. During this process we assumed that this patent was completely valid, and then meticulously designed around its claims with the assistance of a knowledgeable patent attorney. Despite the many limitations this imposed, we succeeded in developing workable optics. Based on the opinion of our patent counsel, we do not believe our product infringes on this patent.How does a Digitarium system compare to an analog Starlab projector?The digital technology used in a Digitarium system offers many advantages over portable analog (pinhole) systems like Starlab. For example:
In short, a Digitarium system offers tremendously more flexibility, capability, and cost effectiveness than a portable analog system. See our products page for more information. How does your Digitarium Gamma Portable compare to the Digital Starlab projector?Based on publicly available information, these are the most important differences that we see between these two systems. (LTI will not allow any of our staff to see their system.)The Digital Starlab:
The Digitarium Gamma Portable:
How does your Digitarium Alpha 2 compare to the MirrorDome system?The MirrorDome system, developed at Swinburne University in Australia, consists of a portion of a spherical mirror, a data projector aimed at the mirror, and a computer running specialized software. The software has to "warp" each video frame before sending it to the projector in order to counteract the severe distortion from the mirror. After reflecting off the mirror images are projected onto a dome. The MirrorDome system:
The Digitarium Alpha 2:
Our Digitarium Alpha 2 and 5m dome costs $27,230. In the US, a MirrorDome from e-planetarium starts near $36,000 (unclear if a dome is included) as of February, 2008. A similar product, the Newtonian 1 with 5m dome is $22,140 from the same source. Using a spherical mirror for planetarium projection has many drawbacks. In particular we would highlight the typical lack of full sky projection, warping artifacts (especially with starfields), and the bulky setup. Plus you miss out on the many benefits of a Digitarium, including the uniquely easy to use handheld remote control interface. For astronomy educators the sheer number of pixels projected is simply not the most important feature of a planetarium system. We believe the main application for spherical mirror type systems is for projecting high resolution wide angle movies at lower cost than with a fisheye lens. The lower quality projection is not as noticeable with bright movies with lots of gradations. A spherical mirror is also an option when a fisheye planetarium system is out of reach. In that case we would recommend putting together your own system for a fraction the cost of a pre-assembled system. Stellarium planetarium software, which we help develop, is free and already includes a spherical mirror warping mode. So all you need is a mirror, a compatible projector, a computer, and time to put it together. Here is a FAQ on the subject. What does it mean that some competing systems have truncated projection?Systems with a truncated projection do not project over a full hemispherical dome -- some portions of the sky are not projected. Usually truncation is a tradeoff to reduce costs or improve resolution in the areas that are projected. Digitarium Systems are true full-dome systems and project the entire sky with a full, uninterrupted horizon onto a dome. We feel that for astronomy education having a full sky projection is critical. The whole point of a planetarium is to immerse the audience in a full simulation of the night sky so that three dimensional concepts can be experienced first hand. Having empty black areas in the sky makes both teaching and learning in a planetarium more difficult for obvious reasons. Here is a visual comparison of approximate sky coverage for 1.) a fulldome system such as a Digitarium, 2.) a spherical mirror system with a 4:3 aspect projector, and 3.) a truncated 4:3 aspect fisheye projection system. Red areas are areas with no projection coverage. 
Software FeaturesWhat software does a Digitarium system run? Can it run Starry Night, Celestia, The Sky, etc.?Digitarium systems run Stellarium, an open source planetarium program. You can connect a separate computer to the projector to project other applications. However, the application needs to support fisheye rendering (polar projection) to be useful. You also must make sure that this use doesn't conflict with the software's license.
For example, retail versions of the planetarium software Starry Night can not be projected using a Digitarium system
because the Starry Night end user license agreement prohibits use with an audience. (There are dome versions which
can be used with an audience, but these can not be purchased independently of
certain planetarium systems.)
From what culture(s) are the constellation labels, line drawings, and artwork?Currently we have line drawings, labels, and artwork for the 88 official Western constellations, as well as line drawings and labels for Polynesian, Chinese, Navajo, Lakota, Inuit, Norse, and ancient Egyptian constellations. We plan to add constellations from more cultures. When available, customers will be able to download the changes using the Digitarium system's software update feature.I don't know anything about the Linux operating system. Will I still be able to use a Digitarium system?You don't need to know a thing about Linux to run the system. You can't even tell what operating system is running, as the system is operated via a hand-held remote control.How do I get software and image updates?Hook your Digitarium system up to an ethernet network with Internet access (see the user manual if you need more information on this), bring up the menu, scroll down to “Administration,” then select Administration sub-item “Update me over the Internet.” The projector will do the rest for you. Software updates are free for the life of your system.What formats are supported by the Digitarium system's multimedia player?MPEG-2 is the best supported video format. If you have a question about a specific format, contact us.Are prerecorded shows available for the Digitarium system?Fulldome video prerecorded shows or segments are available from third party producers and distributors such as:
Inflatable DomesCan I use my Starlab dome with a Digitarium system?Yes, a Digitarium system will work with any portable dome. However, if you project anything besides dark starfields you will see the extensive wrinkling in the silver StarLab domes. The reflective surface is also problematic. The Digitalis dome is specifically designed to be used with digital projectors. Our design has fewer wrinkles and no entrance tunnel interrupting the projection surface.Can I set up a Digitalis dome outside?No. Setting up a Digitalis dome outside is strongly discouraged. The dome is lightweight and could blow away, harming your audience or equipment, plus the outdoor environment could damage your dome.Is the Digitalis dome handicapped accessible?Yes. The dome does not have a solid floor; the wall of the dome wraps around and creates a skirt about 18 inches/45 cm wide which rests on the floor. To admit a person in a wheelchair, simply lift a side of the dome and push the wheelchair under. This process is much easier if you have a second person to help you lift the side of the dome. Once the dome is lowered back to the ground, it will reinflate fully in about one minute. What is the procedure for an emergency exit from a Digitalis dome?As mentioned above, Digitalis domes do not have a solid floor, so audiences can exit the dome very quickly by lifting the side and ducking under. Why do you use such a small dome at trade shows?We usually use a 9 foot diameter dome at conferences to economize on exhibit expenses so that we can keep our prices as low as possible. Keep in mind that a competitor displaying a larger dome usually is spending almost four times as much on exhibit space, which adds up quickly.GeneralHow can I see a Digitarium system in use?Go to our see one page to review our conference schedule and demo policy, or contact us.Can someone at Digitalis help me apply for a grant or sponsorship?Yes, you can contact Karrie Berglund, Director of Education, for help with funding proposals. However, please first read our funding page to see if it gives you the information you need. What kind of maintenance is required by the projector and dome?Very little. The projector lens will need to be cleaned from time to time with a soft, lint-free cloth and alcohol (see your user manual for more information), and lamps will need to be replaced when they burn out or reach the end of their design life (the projector tracks usage information for you). You should have your system checked for dust accumulation once a year and cleaned if necessary. The dome can be cleaned with a damp sponge if needed.Is there a warranty for your products?All our equipment has a two year limited warranty, which you can read on the order form.PurchasingDo you accept credit cards?No. See the sale terms on our order form for acceptable forms of payment. How long does it take to get a Digitarium system or Digitalis dome?Typically one to eight weeks, depending on inventory levels. We try to stock all the products we sell. Contact us for a current turn around estimate.How do I find out if there is a local distributor in my country?All of our distributors are listed on our contact us page.I want to be a sales agent or distributor for your equipment. What do I need to do?Contact us to discuss the possibility. | |
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