Celestron 8" EdgeHD optical tube, CG-5/AVX dovetail


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The EdgeHD high definition flat field optics of this Celestron 8" EdgeHD optical tube make true astrographic-quality 8" optics truly affordable . . .
Our Product #: C8HDOTA5
Celestron Product #: 91031-XLT
Recommended Accessories

Product Description

This Celestron EdgeHD 8 optical tube (CG5) has:
• 8" EdgeHD Fastar-compatible high definition aplanatic Schmidt-Cassegrain optics
• StarBright XLT optical multicoatings for the highest possible light transmission
• mirror locks and cooling vents
• 9 x 50mm finderscope in quick-release bracket
• 1.25" star diagonal
• 40mm 1.25" Plössl eyepiece (51x)
• CG-5/AVX Advanced Series (Vixen-style) dovetail
• 2-year warranty

The compact and easily transportable Celestron 8" EdgeHD optical tube has new and unique 8" aperture aplanatic (free from coma and corrected for spherical aberration) EdgeHD high definition/high contrast Schmidt optics. The advanced EdgeHD optical system uses a dedicated dual-element field flattener lens made from premium Schott optical glass in its central baffle tube to reduce off-axis coma and produce aberration-free images across a wide 42mm image circle (as large as the diagonal of a 35mm negative or large format CCD chip and ideal for astrophotography).

In addition to reduced off-axis coma, the EdgeHD optics deliver an astrograph-quality focal plane more than three times flatter than standard Schmidt-Cassegrains and dramatically flatter than competing coma-free designs. Stars are smaller and more concentrated, creating brighter images and allowing you to see down to a fainter magnitude than other equally-sized telescopes. With EdgeHD optics, you see sharp point-like stars to the very edges of some of the largest CCD and DSLR chips available today.

For the ultimate in brightness and contrast, the 8" EdgeHD optical tube has state-of-the-art Starbright XLT multicoatings. Its light grasp is almost 850 times that of even the sharpest dark-adapted eye, revealing to your eye and camera star clusters, nebulas, planets, and galaxies in amazing detail. The Fastar-compatible optical tube even allows imaging down to an incredibly-fast f/2 focal ratio using optional accessories.

This Celestron Optical Tube's Optics . . .

EdgeHD aplanatic Schmidt-Cassegrain optics: 8" aperture (2032mm focal length f/10). Guaranteed diffraction-limited optical performance, free from coma and corrected for spherical aberrations (aplanatic design). Dual-element field flattener lens built into central baffle tube. The 17" long aluminum optical tube has a large handle on the rear cell and weighs only 14 pounds, making it easy to transport and assemble the optical tube to a mount in the field. For more details, click on the "EdgeHD optics" link in the support tab above.

StarBright XLT fully multicoated optics: This high transmission/high reflectivity optical coatings package applied to each optical surface gives you visibly higher light transmission for brighter deep space images and shorter exposure times during imaging. It also increases the contrast on subtle lunar, planetary, and nebula details when compared with optics using ordinary coatings or multicoatings. For more details, click on the "Starbright XLT" link in the support tab above.

Fastar compatible: For the ultimate in wide-field catadioptric imaging, the EdgeHD optical tube is Fastar compatible to allow CCD imaging at a blazingly-fast f/2 focal ratio. For f/2 imaging, an optional Fastar lens assembly lens replaces the scope's removable secondary mirror (an exchange that takes only a few minutes). Your CCD camera is attached to the Fastar lens. This puts your camera at the f/2 position in the center of the Schmidt corrector lens at the front of the optical tube, rather than in its normal f/10 position at the Cassegrain focus at the rear. The Fastar option is for imaging only and cannot be used for visual observing.

This Celestron Optical Tube's Mechanics . . .

Focusing: Focusing is accomplished by turning a knob on the rear cell that moves the primary mirror fore and aft along the central baffle tube to adjust the focus. The Celestron focusing mechanism is supported by two pre-loaded ball bearings, minimizing the "mirror flop" typical of bushing-type focus mechanisms that causes image shift during critical focusing.

Mirror locks: Flexible tension locks hold the mirror in place after correct focus is achieved for imaging and reduce image shift when rotating the tube around a mount (when moving past the zenith during astrophotography, for example). Unlike other designs that have only one locking knob located off to one side of the mirror, the Celestron system uses three locks equally spaced around the mirror to distribute the mirror locking force symmetrically.

The focuser itself acts as one of the locks, while two flexible rods spaced 120° away in either direction act as the second and third locks. Controlled by variable tension knobs on the rear cell, these rods act in conjunction with the focuser to hold the mirror in place without putting any asymmetrical force or pressure on the mirror. This keeps the image centered in the eyepiece (or chip) no matter what the orientation of the optical tube.

Tube vents: Two cooling vents on the rear cell allow warm air to be released from behind the primary mirror when the scope is taken out for a night's observing or imaging. This shortens the amount of time needed for the optics to cool down to ambient air temperature for peak performance. Each vent has an integrated 60 micron micro-mesh filter guaranteed to let warm air out without letting dust in.

Dovetail rail: The full length dovetail rail mounted under the optical tube fits Celestron CG-5 Advanced Series mount, as well as any other make or model German equatorial mount that uses a Vixen-style mounting dovetail slot.

This Celestron Optical Tube's Supplied Accessories . . .

Finderscope: The supplied 9 x 50mm straight-through achromatic design finderscope has a wide 5.8 degree field of view. It is mounted in a spring-loaded easy-adjust quick release bracket.

Star diagonal: The supplied star diagonal is a 1.25" prism type. Also included is a 1.25" visual back.

Eyepiece: The standard equipment eyepiece is a 1.25" 40mm Plössl (51x). The eyepiece field of view is 0.84 degrees, almost 70% larger than the full Moon.

Two-year warranty: All Celestron optical tubes have a two-year warranty.

Tech Details

Aperture 8"
Focal Length 2032mm
Focal Ratio f/10
Highest Useful Magnification 405x
Weight 14 lbs.
Optical Coatings StarBright XLT fully multicoated
Resolution 0.57 arc seconds
Supplied Eyepiece 1.25" 40mm Plssl eyepiece (51x)
Telescope Type EdgeHD
View Finder 9 x 50mm finderscope
Visual Limiting Magnitude 14 arc seconds
Warranty 2 years


Review by:
I agree with the comments by "Daniel" above.
I had an old Celestron C8 dating back to the late 80's. I converted it from a fork mount to a OTA put it on a good german equatorial mount. This scope served me very well for nearly 30 years and was used mostly for visual deep sky and some photography of moon and planets. The old scope did not have the enhanced coatings and had a few mechanical issues. I debated for quite some time whether it was worth upgrading to the C8 Edge, but bought the C8 Edge with the Losmandy base plate.

After about a month of using the new Edge a half dozen times, and comparing the scopes side by side, I did not regret the upgrade. First, the focuser is much better than the old scope in both fine focusing and much less mirror shift. That alone was worth the upgrade! Second, the contrast is much better, for example, the moon contrast is dazzling Third, the field of view is flatter and can be noticed visually. I have not yet tested it with a DSLR yet. The resolution on double stars seemed about the same, as expected. It does still need the cool down time much like the old scope although this is hard to test definitively, but I suspect the vents are mainly for equalizing the air pressure as the assembly is sealed because of the internal flattener lens. I have not yet been able to test how the scope performs when it is used with back focal point that differs significantly from the recommended distance needed by the flattener. There are times that it is necessary for some accessories. Check out Celestron's Edge white paper for info on this.
As for negatives:
1) the finder (straight-thru) and the diagonal look and feel cheap. The finder mount is not the common undersized dovetail, it is a "peculiar" mount. I replaced the finder and it's mount immediately .
2) The Losmandy-style (3") dovetail was not immediately compatible with my Ioptron ieq45 saddle, it was slightly narrow. I had to glue a very thin brass shim on the mount saddle to use the scope.
3) I wanted a Vixen-style dovetail on the top of the scope and keep the stock losmandy dovetail on the bottom for a variety of reasons (adding guide scopes, movable weights, and the ability to the scope on vixen-only mounts). Most vixen dovetails can not be mounted directly on the top of the scope without buying radius blocks ($35) from ADM accessories, or their dovetail/radius blocks set.
Otherwise, I am happy with the new scope and I got $350 selling the old scope.
(Posted on 10/6/2019)
Review by:
I actually love this scope despite the 4 star review. I'd give it 5 but for the cheap accessories that Celestron includes. Look, Celestron does make good stuff, but if buyers are "stepping up" to the EdgeHD line over the "base" 8" SCT, then why stick them with a crappy 1.25" visual back and an equally crappy diagonal? Furthermore, a straight-through finder scope is a pain in the neck - literally - to use with an SCT, unless you are two feet tall or don't mind grovelling on the ground to do your "all-star" alignment (assuming you are using a Celestron mount) and trying to crane your neck to use some star that isn't near the horizon.

What this kit SHOULD have: a 2" visual back (click-lock, if possible), a proper 2" star diagonal, and a right-angle finder. Users of this scope will end up having to buy all this stuff to get the most out of this telescope, anyway. Might as well start them off right!

Put to good use, the image this provides is worth it - beautifully corrected, crips, contrasty - a wonderful moderate-aperture planetary (mainly) scope.

Despite the correction for photographic purposes, I would strongly advise NOT using this for DSO photography. As this is still priced low enough to be attractive for entry-level would-be astrophotographers, imaging at f/10 at 2000mm focal length is NOT for the faint of heart or the inexperienced. If your interest is planetary imaging, you would be better served (at the same price) - by a non-EdgeHD larger aperture SCT since you only need the center, rather than the edges of the field to be flat for photography.

So why buy this scope if it's not actually ideal for DSO astrophotography or planetary imaging but still produces an image plane that is highly corrected suggesting photography as the intent? Because it's wonderful for visual use - better than the "base" 8" SCT. The "base" SCT shows its flaws with all but very good eyepieces and is limited in its ability to get the most out of better or high-end eyepieces. The EdgeHD on the other is already highly corrected and so can provide very nice views with modest eyepieces and when paired with nicer glass from, say, Televue, can really show nice views from edge to edge. (Posted on 9/13/2019)
Review by:
I owned this scope and regret getting rid of it. The views from it were absolutely stunnning. Mars, Jupiter, Saturn, never have I owned a scope that gave me such amazing views of these celestial bodies. If you are on the edge of buying one, I highly recommend it! (Posted on 9/10/2019)
Review by:
I owned this scope and regret getting rid of it. The views from it were absolutely stunnning. Mars, Jupiter, Saturn, never have I owned a scope that gave me such amazing views of these celestial bodies. If you are on the edge of buying one, I highly recommend it! (Posted on 9/10/2019)
Review by:
I really love this telescope. I use it with an unmodified DSLR for imaging and it has been great. I added the .7 focal reducer and spent a fair amount of time practicing alignment and improving the mount tracking but when the tracking is dialed in the pictures are wonderful. (Posted on 7/24/2019)
Review by:
I was looking for something faster to set up than my NexStar11GPS but bigger than my Vixen NA140, with less colour. I was looking hard at a C8 when a user on CloudyNights recommended the Edge. I liked it so much on my Losmandy Alt-Az mount I ended up getting the SE mount for it (less thrilled with the SE mount so I'm looking at the new Edge mount).

Folks are right, smaller scopes get used more than big scopes. While I have let the hobby slide a bit, I keep this scope next to the door and I take it out for quick views when the mood and the sky converge. (Posted on 7/22/2019)
Review by:
I recently upgraded from a 1999 C8 and immediately noticed a difference for both visual observing and astrophotography. The mirror locking mechanism holds the mirror in place... no more mirror flop. I put this on an CGEM II mount and use Sky Safari with Sky-Fi III to control it. Great setup and worth every penny. (Posted on 12/24/2018)
Review by:
I have mine on an Atlas Pro mount. So far I got great images of Mars, Jupiter and Saturn. This scope is also a pleasure for visual use. Factory collimation came spot-on and the star test was almost 100% perfect. Unfortunately it’s been raining non-stop for the last two months and I have not been able to do DSO imaging but I know it will yield wonderful images. (Posted on 11/9/2018)
Review by:
A fantastic lightweight great light grasp scope. Add in the Deep Space Products TEMPest fans and a 2" diagonal and you are good to go with a fantastic visual scope that is super light and easy to move around with. Put it on a Celestron AVX with the Celestron StarSense and you have a Roboscope that can align itself while you grab a cup of hot cocoa with butter or whatever your choice of warm beverage is. (Posted on 10/26/2018)
Review by:
Side by side comparo vs. my 2015 black tube standard C8. The Edge version outperforms across the board. Stars are sharp to the edge of field, even with ES 82* eyepieces. Much less focus shift - a real easy to use OTA. Slightly heavier, though my Twilight II and Great Polaris mounts handle it very well. (Posted on 10/24/2018)
Review by:
I have this and love it. I think the 8” Edge HD is the best optical tube Cekestron makes. The 8” collects plenty of light, but is still relatively small and light. Great for photography and visual use. No regrets! (Posted on 10/7/2018)
Review by:
I am now pushing 70 and decided to downgrade from my 11 inch Edge HD. This is much easier for me to manage along with the new mount IEQ45 from Ioptron it is much easier to load, setup and I love it. (Posted on 10/6/2018)
Review by:
Mine is mounted on a Losmandy GM8 and works very well. It is light enough to grab and go while still providing a good amount of light gathering capability. Imaging with a Canon 6D and t-adapter has worked well for me thus far.

I added a 2nd dovetail rail to mount a William Optics GT71 as a guide scope. They compliment each other very well. I suggest getting the Celestron soft carrying case. It makes protecting your investment much easier. (Posted on 10/6/2018)
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Supplied Accessories

Starbright XLT fully multicoated 8" f/10 Fastar-compatible EdgeHD optics; 9 x 50mm finderscope; 1.25" star diagonal with 1.25" visual back; 1.25" 40mm Plössl eyepiece (51x); dust covers; CG-5 (Vixen-style) dovetail mounting rail.