In the 1990s, Celestron teamed with SBIG to create the Fastar astrophotography system which allowed the replacement of the traditional Schmidt-Cassegrain secondary mirror with a small CCD camera, creating an ultra-fast F/2 astrograph. While the Fastar CCD system was discontinued in 2000, all C-6 through C-14 telescopes still feature “Fastar-compatible” removable secondary mirrors, as indicated by the colorful “Fastar” logo on the face of the secondary holder.
In 2005, Dean Koenig and his associates at Starizona in Tucson, Arizona, created the Hyperstar photographic system. Unlike the original narrow-field Celestron Fastar system, the Hyperstar incorporates a wide field flattener to allow any Fastar-compatible SCT to act like the Celestron Schmidt camera that was revered in the film photography era. The resulting astrograph F/ratio depends on the telescope model used, varying from F/1.9 to F/2.3.
The Hyperstar system was initially offered for both Meade 10- and 14-ich SCTs, as well as Celestron telescopes, but the Meade option is no longer offered due to low demand. Starizona offers a $250 conversion kit to allow early model non-Fastar C-8 telescopes to accept the Hyperstar. Today, Version 4 of the Hyperstar is a coveted accessory that bridges the gap between wide-field camera lens astrophotography and high-resolution prime focus photography.
A needless concern is whether the SCT corrector plate can adequately support the weight of the Hyperstar and camera assembly. The heaviest Hyperstar lens is the 3.1-pound C-14 model. When installed, the lens assembly projects the mass of the camera about six inches out from the corrector. This applies torque to the corrector equal to the camera weight times the length of the Hyperstar, plus the Hyperstar’s own weight. Celestron performed corrector plate load tests to verify the safety of the Hyperstar system and found the failure weight of a mass suspended at Hyperstar distance from the C-14 corrector was 70 pounds. Thus, any camera system installed on the Hyperstar will have a weight safety factor of between five to 10 times the mass of the camera.
The collimation of a Hyperstar has also been the source of angst among astrophotographers, but the process is little different than ordinary Schmidt-Cassegrain collimation when using the Hotech Advanced CT laser collimator and the accessory Hotech Hyperstar reflector mirror. An “eyeball” collimation process can also be done by following the steps outlined in the excellent document “The Amazing HyperStar: A Guide to Optimize Performance”, available online at:
Starizona provides camera-specific Hyperstar adapters for all popular camera types that will have the proper DSLR lens mount or T-threads. The adapter automatically spaces the camera at the proper back focus distance. Camera adapters for the C-6 only accept 1-¼-inch threaded filters for sensor sizes no larger than 11mm, while the C-8 and larger adapters accept 2-inch threaded filters. A Starizona filter slider is also available for the larger Hyperstars to allow changing filters without dismounting the camera. The proper camera-specific filter slider adapter is also needed to maintain correct back focus. Unfortunately, the filter slider will not work with mirrored DSLRs or with the smaller C-6 and C-8 Hyperstars.
The Hyperstar optical system is best matched with an APS-C sized sensor. Full-frame DSLRs will show significant vignetting due to image clipping by the DSLR mirror box. Mirrorless cameras are less prone to vignetting, and dedicated CMOS and CCD astrocameras with the sensor mounted near the front of the camera work best. I have no uncorrectable vignetting issues with my ASI294MC Pro on a C-14 Hyperstar.
The front-mounted camera shadow footprint has minimal effect on the final image if the camera body does not significantly exceed the diameter of the Hyperstar lens itself. Normal-sized DSLR bodies will work on C-9.25 and larger scopes. However, a DSLR will block too much of the aperture with a C-6 and C-8. The smaller model Hyperstars will need smaller cylindrical cameras like QHY and ZWO models to prevent occulting too much of the telescope’s aperture.
Focusing the Hyperstar is performed using the telescope’s standard focus knob. The Hyperstar’s fast F/ratio narrow zone of focus is easy to adjust with a split Bahtinov mask such as the one available from 3-D printing sources like Photon Express (https://jwbozeman.com). Hinged split Bhatinov masks are preferred to eliminate interference by the camera’s power and USB cables. Most Celestron SCTs have temperature-sensitive aluminum tubes and the Hyperstar will need refocusing if the temperature drops as the night progresses.
Since the Hyperstar lens assembly replaces the secondary mirror, the Hyperstar is not a visual instrument. However, the optical power of the Hyperstar is demonstrated when an ultra-sensitive camera like the Sony a7 is installed on a large SCT equipped with Hyperstar. While viewing with the camera’s LCD viewfinder, the target image can often be seen behind the viewer even with it partially occulted by the viewer’s head.
Exposures times with the Hyperstar are surprisingly short and can reach the sky fog limit in seconds unless contrast-enhancing or light pollution filters are used. Exposures that would theoretically take 25 minutes at the telescope’s traditional F/10 configuration take only 60 seconds with the F/2 Hyperstar. The fast Hyperstar optics even allow imaging targets with an alt-az mount. A stack of 20-second sub-exposures will reduce the effect of field rotation and allow stunning images of brighter targets.
The fast Hyperstar imaging system is traditionally regarded as a dark sky instrument but combined with aggressive light pollution filters such as the Radian Triad Ultra F3.0 filter (also reviewed in AstroGear Today), the Hyperstar is a powerful and very viable urban deep sky astrograph. I do all my Hyperstar deep-sky imaging from within a city of two million. The results shown on these pages speak for themselves. A properly filtered Hyperstar is a stunning urban astrophoto tool.
To conclude, what’s not to love about the Hyperstar? Its short focal length simplifies autoguiding, and with proper filtration it allows backyard urban astrophotography that would have been impossible just a few years ago. The Hyperstar lens assembly would be a valued astrophotography accessory for all Celestron SCT owners.
Plus: The Hyperstar lens converts a Fastar-compatible telescope into a powerful Schmidt camera-like astrograph.
Minus: Short focal lengths aren’t suited for smaller deep sky targets.