SEE THE UNIVERSE IN HD
Introducing Celestron's New Aplanatic Schmidt Telescope Design!
EdgeHD is an aplanatic Schmidt telescope designed to produce aberration-free images across a wide visual and photographic field of view. The optical system was designed to reduce more than just off-axis star coma, but also to give an astrograph quality flat focal plane all the way to the edge of the field of view.
The Celestron Product Development team has released a whitepaper outlining the technology behind EdgeHD. This paper describes the development goals, design decisions, optical performance, and their practical realization in 8-, 9.25-, 11-, and 14-inch apertures. We include cross-sections of the EdgeHD series, comparative spot diagrams for the EdgeHD and competing “coma-free” Schmidt-Cassegrain designs, a table with specifications for visual and imaging, graphics showing how to place sensors at the optimum back-focus distance, and details on the construction and testing of the EdgeHD telescope series.
True Astrograph Quality
Many optical designs that advertise themselves as "astrograph" quality actually only produce pinpoint stars across a curved focal plane. While this may be acceptable for visual observing, stars will appear out of focus at the edge when used with a flat chip sensor of a digital camera. EdgeHD optics produce a focal plane more than three-times flatter than a standard Schmidt Cassegrain telescope and dramatically flatter than other competing coma-free designs. This guarantees you visibly sharp stars across some of the largest CCD chips available today.
Superior edge performance not only creates rounder, more pleasing stars but actually improves the resolution and limiting magnitude when compared to telescopes of equal aperture. Starbright XLT® Coatings coupled with Celestron's StarBright XLT coating group on every surface, EdgeHD optics gives you maximum light throughput across the widest visual and photographic spectrum.
In addition to Celestron’s new optimized optical design, the EdgeHD tube has been redesigned to make sure you get the most from your optics each and every night.
Mirror Clutches - Flexible tension clutches hold the mirror in place and reduce image shift when rotating the tube around the mount. The flexible rods allow the mirror to be held in place without putting any force or pressure on the mirror assembly, keeping the image centered in the eyepiece (or chip).
Tube Vents - Cooling vents located on the rear cell allow hot air to be released from behind the primary mirror. Each vent has an integrated 60 micron micro-mesh filter guaranteed to let warm air out without letting dust in.
Fastar Versatility - The EdgeHD is the most versatile imaging scope available today. At its native f/10, you can achieve the image scale necessary to capture the smallest of deep sky objects. With the optional reducer lens (coming soon), you can increase your field of view without sacrificing optical performance. A barlow gives you the added power for high resolution planetary, lunar and solar imaging. And of course, all EdgeHD optical tubes are Fastar® compatible for ultra fast f/2 wide field imaging. Each tube has been fitted with a removable secondary mirror and are opto-mechanically aligned on a laser bench to ensure they are axially symmetric in any configuration.
CGE PRO Tracking Data
The following graphs display R.A. worm gear tracking accuracy of the CGE Pro Equatorial mount in 4 conditions: Figure 1 – Raw unguided tracking that isolates the periodic error; Figure 2 – Tracking with Permanent Periodic Error Correction (PPEC) enabled; Figure 3 – Guided tracking with an autoguider; and Figure 4 – Guided tracking with an autoguider and PPEC enabled. Data was acquired from Celestron’s engineering team using an EdgeHD 800 optical tube and NexImage camera at f/10. This data represents the typical performance of a CGE Pro under average seeing conditions from urban skies in Torrance, CA. Figure 2 has a cubic fit applied to the graph, and Figures 1, 3 and 4 have linear drift removed (to better show repeatable error). All Figures show 22 minutes of tracking, which covers 4 full rotations of the CGE Pro R.A. worm gear.
Figure 1. This graph displays the R.A. worm gear tracking accuracy for a typical CGE Pro equatorial mount. The graph shows 4 periods of the worm gear which yields about +/-7 arc seconds of periodic error. The minimal periodic error is both very predictable and gradual, allowing short unguided images to be taken, or much longer exposures with extremely accurate tracking when used with an autoguider.
Figure 2. With the CGE Pro’s Permanent Periodic Error Correction (PPEC) enabled, most of the periodic error is eliminated, leaving behind lesser tracking errors caused by atmospheric turbulence, wind, and opto-mechanical flexure. PPEC brings the CGE Pro’s R.A. tracking accuracy to about +/-2 arc seconds, allowing even longer unguided exposures (for uses like Hyperstar imaging).
Figure 3. Autoguiding with the CGE Pro provides consistent tracking accuracy to within +/-2 arc seconds under average seeing conditions. Autoguiding provides an easy way to sustain long-exposure astro-images without excessive tracking error or drift.
Figure 4. With autoguiding and PPEC enabled, we can take full advantage of the CGE Pro’s stability and tracking accuracy. Even under average seeing conditions, PPEC + autoguiding easily yields tracking accuracy of less than +/-2 arc seconds. Note that tracking errors of the mount have dropped so far below the noise floor set by the seeing conditions that they cannot be quantitatively distinguished from zero. This combination will provide the best tracking accuracy, resulting in sharp, round stars in your astro-images.
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