Digistar II

Digistar II is a planetarium projection system by Evans & Sutherland - Digistar Users Group. It was released in the early 1990s as a descendant to the earlier Digistar, developed in the late 1970s. The system has been replaced by its full-dome descendant, the Digistar 3.

The Digistar II which is, in many ways, a direct upgrade of the original Digistar projection system, was an early attempt at full-dome video. Unlike true full-dome video, Digistar and Digistar II are vector graphics based, rather than raster based. As such, neither of these systems can provide full-color, rendered effects. Evans & Sutherland's newer system, the Digistar 3, can do so.

Unlike modern full-dome systems, which use LCD, DLP, SXRD or Laser projection technology, the heart of the Digistar II is a large cathode ray tube. A phosphor plate is mounted atop the tube, and light is then dispersed by a large lens to cover the planetarium dome. The use of a CRT means the Digistar II has a darker black-level than full-dome projectors, but, as it is only one tube, the D2 is monochromatic. The Digistar II projects a bright, phosphorescent green—though many (including both visitors and planetarians) report they cannot distinguish between this green and white.

Due to the use of vector graphics, as opposed to raster imaging, the Digistar II does not have the resolution issues that many full-dome systems have. Thanks to this, and the brightness of the CRT, only one D2 projector is needed to project on the entire dome (most full-dome systems require between 1-6 raster projectors, depending on dome size).

As Digistar II was being developed, many planetaria were sold Digistar LEA projectors. The LEA, called Digistar 1.5 by many users, is effectively a prototype of the D2 projector, compatible with Digistar and upgradable to Digistar II. There are no significant differences in performance between the LEA and the true D2.

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