Celestron’s EdgeHD telescopes represent a major advancement on both the optical and mechanical features of their renowned Schmidt-Cassegrain telescopes.
From an optical point of view, EdgeHD is an aplanatic flat-field Schmidt optical system developed to produce aberration-free images with pinpoint stars all the way to the edge of the field of view of today’s largest imaging sensors and wide field eyepieces. The EdgeHD optics virtually eliminates both field curvature and off-axis star coma, providing an astrograph-quality system at a fraction of the price of competitors. EdgeHD optical tubes are sold separately or paired with our most popular telescope mounts.
Many current optical designs advertise themselves as “astrographs,” but only produce pinpoint stars across a curved focal plane. This means that when focused sharply in the centre of the field of view, this curved plane cannot bring stars at the edges into focus and the more pronounced this defect becomes with a wider the field of view. Although this may be acceptable for visual observing, when a curved plane is paired with the flat sensor of a digital camera, stars become noticeably out of focus towards the edges.
Celestron’s 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, guaranteeing you visibly sharp stars all the way across the imaging sensor.
A curved focal plane cannot produce consistent results on a flat CCD chip. Stars will appear out of focus at the edges.
Now, if you compare the two images of M3 below. The first was taken with a competing coma-free optical design, the second with EdgeHD. Both images were taken with the same 35 mm chip (42 mm diameter focal plane) camera under the same conditions.
When focused on-axis, both images appear to be sharp in the centre. But in the first image, as you examine the stars closer and closer to the edge, the stars become larger and less focused. Finally, at the very corners, the stars are so de-focused that they appear as rings instead of pinpoints.
Now look at the second image. As you move from the centre outward, the stars retain their focus from edge to edge, appearing as crisp, solid points of light.
Superior edge performance not only creates rounder, more pleasing stars, but actually improves the resolution and limiting magnitude compared to telescopes of equal aperture.
Celestron’s high definition optics let you resolve smaller spot sizes all the way to the outer edge, revealing finer detail and greater contrast. Compare the two cropped images below, both taken with a 37 mm chip (52 mm diameter focal plane) camera.
What’s more, EdgeHD optics give you smaller, more concentrated stars so you can see fainter magnitudes than with other equally-sized telescopes. Poor edge quality can spread out starlight so much that the brightness of a star appears the same as the sky background, making it undetectable to your eye or camera. With EdgeHD optics, you can capture the faintest of galaxies all the way to the corner of your full-frame camera chip. Compare the two cropped images below, both taken with a 37 mm chip (52 mm diameter focal plane) camera.
All EdgeHD optical tubes also feature Celestron’s StarBright XLT coating system on all mirror and lens surfaces. When added to the EdgeHD optical system, StarBright XLT provides maximum light throughput across the widest visual and photographic spectrum. Learn more about StarBright XLT.
The Celestron EdgeHD tube features innovative mechanical designs to ensure you get the most from your optics each and every night you use the telescope whether it is for visual or imaging purposes.
- Mirror support: Flexible tension clutches hold the primary mirror in place and reduce image shift. The flexible rods hold the mirror in place without putting any force or pressure on the mirror assembly, keeping your target 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 micromesh filter guaranteed to let warm air out without letting dust in.
- Fastar versatility: EdgeHD is the most versatile imaging telescope available today. At its native f/10, you can achieve the image scale necessary to capture the smallest of deep-sky objects. To increase your field of view without sacrificing performance, add the optional EdgeHD reducer lens. Each one is custom-made for your size EdgeHD optical tube and brings your focal ratio down to f/7. A Barlow lens provides additional magnification 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 EdgeHD tube is fitted with a removable secondary mirror and is opto-mechanically aligned on a laser bench to ensure it is axially symmetric in any configuration.
- Easy collimation: Guarantee ideal performance every time. Edge HD’s precision-machined mechanics and a spherical secondary mirror make collimation simple and accurate.
If you want the full story behind Celestron’s EdgeHD optics, the Celestron’s Product Development team has released a whitepaper outlining the development of EdgeHD, the manufacturing and QA process, and how to get the most out of your system. It also includes 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, and graphics showing how to place sensors at the optimum back-focus distance for astroimaging.