iterations of Digistar replaced the physical control panel with a common graphical user interface. Digistar 3 was the first Digistar system to offer full-dome video in 2002, using six projectors. Digistar 4 was able to cover the dome using only two projectors. System limitations Though technologically advanced in its day, and the closest system to true full-dome video at the time of its release, the original Digistar and Digistar 2 are limited to only projecting dots and lines—meaning only wireframe models can be projected. To compensate for this, the projector is capable of defocusing specific models, blurring lines and dots together. An example of this is in the Digistar 2's built-in Milky Way model. The model is a circle of parallel lines that, when defocused, appear as the continuous band of the Milky Way across the sky. On more complex models, especially three-dimensional ones, brightness and details may be lost in this process, so it is not useful in all situations. The Digistar and Digistar 2 also suffer focus limitations. Because they use a single lens to cover the entire dome, it is difficult to gain perfect focus across the dome. Coupled with this, stars greater than a certain brightness are "multihit" points, meaning the projector draws two dots at the given position to accommodate the brightness of the star. Errors in the projector can lead the second dot to be slightly out-of-place with the first one. These two issues together, along with other issues that can occur within the projector's focus system, give the stars a blobby look. Some planetarians, used to the pinpoint opto-mechanical projector stars ubiquitous in the day, rejected the Digistar and Digistar 2 because of this, ignoring the other advantages of the system. The CRT in the Digistar and Digistar 2 begins to burn out and lose brightness after roughly 1000 hours of use. This means most planetariums must change out the tube after every year or year-and-a-half. File types While the original Digistar ran on large VAX computers, Digistar II runs on the much more compact and advanced Sun Microsystems SPARCstation 5. D2 uses two primary file types, .vl and .sf. .vl files are binary model files, while .sf files are binary show data files. Model files contain vector, line and dot data, as well as parametric changes to data within the file. Show files contain commands to the system, regarding the manipulation of