Reviewed in the United States on May 10, 2020
I wrote up my experiences with the EdgeHD, the 700 Mak-Cas., and a 6 inch APO triplet refractor.
The EdgeHD 800 is an 8-inch Schmidt Cassegrain that is touted to have exceptional edge sharpness with both photographic and visual benefits. I had purchased an orange Celestron C8 in the ‘80s, and now getting back into the hobby after a decade and a half long hiatus, the Nexstar Evolution EdgeHD 800 with StarSense seemed a perfect place to jump back into the hobby. The Celestron 700 is a 7-inch Maksutov Cassegrain that is touted to have excellent contrast most suited to solar system viewing as well as improving the perception of light-polluted skies. So, living in light-polluted Jacksonville, FL, where I find solar system viewing most sustaining, I found the 700 Mak. to be most intriguing.
I managed to save up $777 to buy a Celestron C-8 when I was a teenager. I enjoyed the hobby until I was divorced and ran into hard times and was forced to give up extravagances. I did not purchase a new scope until recently, after some 15 years of hardly looking up. I am sort of compulsive and occasionally impulsive when it comes to my hobbies. Whether it be model trains or airplanes, aquariums or preparedness, I usually buy too many things and wind up reselling most on eBay. As it turned out, my reentry into the hobby resulted in the purchase of 10 telescopes! I don’t beat myself up about this irresponsibility because my enthusiasm requires much fuel, and I can enjoy a wider range of optics and gain useful insights into the hobby that I otherwise would not.
My timing was partly inspired by the opposition of Mars that will occur in 2020. We will be closer to Mars this year than we will for longer than I will live. I’m in my fifties, and I’m beginning to think in terms of bucket lists. I want to experience some things that I’ve always wanted to before my time is up. I have a particular interest in Mars and have conducted scientific research on the subject of Martian glaciers. In some sense, it’s a sort of hobby as well because I am an independent researcher and only work on my Mars projects when I am inspired to do so. Although a telescope cannot begin to reveal the details that Mars orbiters have, the hobby of telescopes is about something special that can’t be duplicated with technology. It’s that personal connection to the cosmos and the cosmic perspective that is derived from it that compels us to stargaze. There are all those cool optics and gadgets, as well!
I managed to get hold of two EVO mounts for the test. Mounting the 700 Maksutov required a little hardware and ingenuity because the EVO mount accepts the narrower Vixen mounting bracket. An Orion dovetail adapter was used along with a custom spacer to allow the adapter to clear the curved mounting dock meant to hug the OTA. This is a less than ideal solution because it sets the optical tube assembly (OTA) about an inch further back than is the case with the 8-inch Schmidt. At 18 lbs., the 700 Mak. is 6 lbs. heavier than the 8-inch EdgeHD 800 but is still within the mount’s load limits because it can handle a 20 lb. 9.25-inch OTA. Balance is also too far forward as the front corrector of a Maksutov-Cassegrain is thicker and heavier than that of a Schmidt-Cassegrain and a Maksutov-Cassegrain tube is longer as well. This could be remedied with a weighted visual back or 2” to 1.25’eyepiece adapter. Properly balanced without any counterweight, the OTA is not far enough forward to reach the zenith. Another option would be to slide the tube forward beyond the balance point for adequate clearance while the tube is in the near-vertical position. When the tube is near vertical, the balance issue is much mitigated because the force of gravity is mostly transferred through the axis of the mount point, generating little torque. However, please return the OTA to the balance point or a bad accident may happen if the tube rotates down under the pull of gravity.
The eyepieces for the test are two Tele Vue DeLite’s. One is an 18.2mm that yields 148x with the 2700mm focal length 700 Mak., and the other is a 13mm that yields 156x with the 2032mm focal length EdgeHD 800. Tele Vue DeLites are considered by many to be top-notch eyepieces for observing solar system detail without false color. An Orion 1 1/4-inch mirror diagonal is mated to the EdgeHD 800, and a Celestron 2-inch mirror diagonal to the 700 Mak.
The first side-by-side test was conducted between 5 and 6:15 am when Jupiter, Saturn, and Mars were some 35 degrees above the horizon and fairly close together. I gave the scope 30 minutes to cool to the ambient temperature of 60 degrees. Jupiter was by far the brightest, followed by Saturn, and then a tiny Mars. The fair seeing was somewhat limiting as far as the test was concerned, with planetary details being limited to the point that the differences in the performance of the scopes would have to be determined by other visual factors. In fact, Mars was completely unresolvable. The Earth’s atmosphere is like a translucent curtain that quivers and induces the shimmering effects more familiarly associated with mirages. Although it is less noticeable than heated air on the horizon, a telescope magnifies even subtle shimmering.
The planets exhibited more ghosting and red and blue color fringing in the EdgeHD 800. Focusing was more precise with the 700 Mak. with moons appearing more star-like. The brightness of the EdgeHD 800 was slightly greater but was not so important in terms of the perception of image quality. The most noticeable difference on this morning was the way Saturn appeared as a ball within a hoop in the 700 Mak., but not the EdgeHD 800. This was the result of the more defined focusing and resolution of the 700 Mak. resolving the planet and its rings as separate forms. This perceived visual “separation” did not occur with the EdgeHD 800 because the two features were not adequately resolved. The difference in the resolution of the clouds of Jupiter was not so great, with both scopes revealing the Great Red Spot. Better seeing would have been required to comment on this point.
As far as the mechanics, I really like the Evolution mount. It is fairly steady and a joy to manually move and track. At about 12 pounds, the lighter weight of the EdgeHD 800 means steadier images and a more comfortable complete setup carrying weight than with it mated to the 18-pound 700 Mak. I can fairly easily carry the complete package with the super-helpful built-in carrying handles. The extra weight of the 700 Mak. caused some back strain and required additional care when moving the complete setup. In light of this, I conclude that the Evolution mount with the EdgeHD 800 is an excellent combination in terms of maximum aperture and convenience, but that it is a bit strained with the 700 Mak. Although one might expect the Schmidt-Cassegrain to cool down faster than the Maksutov-Cassegrain because of its thinner mirror and corrector plate, I did not observe any difference. Would the advantages of light-gathering power, weight, and compactness offered by the 8-inch prove more important to me than some degree of higher optical quality? But how much of a difference?
On the following morning, I decided to test the skies with a smaller scope before lugging out the test subjects. There would be little point of repeating the test under similar seeing. I have a Celestron 127SLT mounted on an Orion VersaGo 2 that is about as handy as anything. I waited for the tube to reach ambient temperatures before casting judgment. The seeing was about the same as the previous morning, so I thought to perform a test of the 127SLT against a Meade 125EXT. Both are roughly 5-inch Maksutov-Cassegrains with the same focal length of 1500mm. The 13mm Tele Vue Delite yielded 115x magnification. Interestingly, the differences were much the same as with the first 700 Mak.-EdgeHD 800 test. The Celestron had a slight edge over the Meade.
Comparing the views through the 5-inch scopes to the 7- and 8-inch scopes, aside from the difference in magnification and assuming similar seeing, the additional resolution provided by an increase in aperture is significant but not tremendous. I believe that 5-inch scopes provide pleasing enough views of the planets to satisfy most people, but the allure of a 7- or 8-inch scope is more important than the additional cost and trouble for many. Of some interest, the Delite exhibited very little false color in the 3 Maksutov-Cassegrains, but more in the Schmidt-Cassegrain. In comparing the DeLites to some standard quality eyepieces, the sharpness and color control are top-notch. In fact, I now consider standard eyepieces to be unacceptable, and this aspect of the test reaffirms my belief that, as I once mentioned to Al Nagler at a star party in the Keys attended by Pluto discoverer Clyde Tombaugh, “an eyepiece is half the telescope”. I came to this conclusion after I purchased the original 13mm Nagler.
It finally cleared one evening, so I decided to test the StarSense technology under a residential, light-polluted location. The number of stars one can see from where I live is pitiful compared to my childhood skies. It seems that endless growth has steadily turned up the dimmer switch of the nighttime skies. The Evolution mount worked with authority as it drove the 8-inch Schmidt-Cassegrain across the sky while the StarSense camera captured and processed images. Although the smartphone app indicated that a successful alignment had been managed, I was unable to calibrate using any star I selected. I tried three times with the same result. Finally, I used the three-star technique of alignment and was able to align the telescope. Perhaps the StarSense technology is not up to the task of discerning the stars from some degree of background pollution. One advantage of the smartphone interface is that precise time is automatically provided. GPS information could also be utilized.
A day later, a morning offered another planet-testing run. Thinking about the satisfying aspects of 5-inch telescopes led to my wanting to test my 127SLT against the 700 Mak. Would the additional 2 inches of aperture prove to be worth the considerable additional weight (tube+mount+tripod), inconvenience, and cost? I also thought of testing the scopes against a 12-inch Meade LX200 SCT. Although bigger scopes produce brighter images and potentially more resolution, this doesn’t always translate to better views because atmospheric turbulence is magnified more in larger apertures. I wondered what threshold of seeing would allow the bigger scope to wring out enough of its greater resolving power to defeat the smaller scopes.
The best planetary images I ever witnessed was produced by a 16-inch Meade Newtonian using a 6-inch offset aperture (again, at the star party in the Keys). This optically less complex and unobstructed arrangement means the crispest of images are generated. Apochromatic (APO) refractors are also capable of near-perfect images. Some have claimed that folded optical systems are flawed in some practical sense by the additional optical elements that must be polished to near-perfection and that their compact form is really their greatest selling point and the reason for their popularity. Interestingly, a company called Astro-Physics makes both APO’s and Maksutov-Cassegrains and claim the 10-inch Mak-Cas they offer for $22K provides APO-like views. Perhaps more complex optical systems require more refinement to overcome their deficiencies. Convenience and optical performance seem to come at a great cost. I wouldn’t be able to test that 10-inch dream scope, but I would have an opportunity to compare the test subjects to an Explore Scientific 6-inch apo triplet refractor.
The seeing was poor in the morning. Jupiter revealed little more than its two equatorial bands. I was using the 13mm DeLite with the 1500mm 127SLT for 115x magnification, and the 18.2mm DeLite with the 2700mm 700 Mak. for 148x magnification. False color ghosting was slightly noticeable in the 5-inch and less so in the 7-inch. Jupiter was both larger and brighter in the 7-inch despite the higher magnification. However, little additional detail could be gleaned from the wavering image. Surprisingly, I found that the image presented by the 5-inch was more pleasing to me. The reason for this could be because the lower magnification brought out less shimmering and resulted in a seemingly steadier image. If the seeing were always this bad or worse, I would be satisfied with the 5-inch for solar system viewing.
The seeing on the following morning was similar to the first test between the 700 Mak. and the EdgeHd 800. I decided to retest the 700 Mak. and the 127SLT. I could easily see the Great Red Spot and the major gap in Saturn’s rings, and I could just begin to make out details like Jupiter’s higher latitude banding in the 127SLT. In the 700 Mak., the Great Red Spot became separated from the equatorial band, and sub-banding within the bands was occasionally visible, as was Saturn’s equatorial bands and more detail in the rings. Further, Jupiter was actually a bit too bright at 148x, so I dropped in the 13mm Delite for 208x. This was about perfect in terms of brightness, but the seeing prohibited seeing any more detail. All in all, the two scopes are a fairly close match with the 7-inch providing about as much additional detail and brightness as one would expect based on aperture alone.
So, is the larger scope worth the higher price and trouble at this seeing level? I can carry the 127SLT and tripod with one hand, while the 700 Mak./EVO setup requires all my attention and much of my strength to move outside. The larger setup costs about 5 times more than the smaller setup. If money were an issue, I would be grateful for the 5-inch. If not, then the additional trouble is worth it for me at least when the seeing is reasonably good.
While waiting for good seeing, I was able to acquire a Celestron CGEM equatorial mount that I will use with the 700 Mak. to solve the clearance issue mentioned before. It is StarSense ready and is a heavy and sturdy mount with a capacity of 40 pounds. This means I can mount my 35 pound 12-inch Meade OTA as well. The LX200 fork and OTA setup is too heavy for me to safely move or transport and the tripod is a behemoth. Altogether, they form what I call a mega-telescope. The OTA + mount+ tripod arrangement will allow me to transport more manageable sections of the telescope. However, mounting the OTA to the saddle is no easy feat for one person. The 6-inch refractor will also be paired with this mount.
The next clear morning, I decided I would pit the 6-inch APO triplet refractor against the EdgeHD 800. The seeing was only fair with 150x magnification being the highest useful power, but I can say that the differences in optical quality were significant. The 8-inch was unable to resolve the details that the 6-inch could. With Jupiter, I could occasionally glimpse subtle details in the cloud bands, and the Galilean moons were resolved to disks in the 6-inch. I could only see about half as much detail in the 8-inch, and the disks of the moons were somewhat lost in unfocused light. On Saturn, the 6-inch presented the planet in 3D, with the outer ring appearing fainter and separate from the inner ring such that Saturn appeared to have two rings of very different character. The faintest of moons were also visible. The 8-inch revealed the Cassini ring division, but the lack of contrast and finer focusing meant the previous impressions were not duplicated. Also, the smaller moons were not so obvious. Mars revealed a dark patch within the mirk of atmospheric turbulence, which was clearer in the 6-inch.
On the positive side of things for the EVO EdgeHD 800 package, the mount was very stable with only a 12-pound load, and the entire telescope, at 45 pounds, was easy to move about fully assembled. In comparison, the CGEM and 20-pound, 4-foot-long refractor shook every time I focused the eyepiece, and the tripod and mount pair, even without counterweights, is a rather awkward and wide, 60-pound octopus to carry and navigate around obstacles. Further, I had to attach the weight and tube assembly under poor light. As far as the optics go, a $1K OTA can’t be expected to compete with one that costs $5k, but the EdgeHD 800 absolutely does provide useful and pleasing views. It is a very versatile and portable package that is, in a sense, like a smartphone, whereas the refractor is more like a high-resolution monitor. I suppose the 127SLT is like an iPod, and the 12-inch Meade is like an old school big screen tv. But where does the 700 Mak, fit in? I guess it would be most like a tablet. Comparing the two telescopes to each other and to the ideal solar system standard that is the 6-inch APO triplet refractor helped me to better observe the difference and to characterize their position in the telescope hierarchy.
On the next morning, I took out the refractor and the 700 Mak. Again, the seeing was only fair, but I was treated to a Jovian spectacle. When a moon crosses the limb of Jupiter, it’s a kind of occultation. Not only was this happening, but a shadow of a moon cast on Jupiter would do the same, and at the same time. The 700 Mak.’s performance was better than I expected set against the high standard of the refractor. The differences were more subtle than with the EdgeHD 800. Airy disks are concentric patterns of light that circle stars and other small and bright objects that all telescopes try to manage as well as possible. Well, the airy disks of the Galilean moons were bright enough in the 700 Mak. to make resolving the moons difficult. In contrast, the airy disks were hard to see through the refractor and the disks were well resolved. Likewise, as the moon and the shadow simultaneously crossed the limb of Jupiter, they appeared more like a pimple and a notch through the 700 Mak. than the clearly defined disks through the refractor.
On Saturn, I could more easily pick out the very faint moons and distinguish the small section of Saturn that protruded from behind the rings in the refractor. Overall, the planet and rings were better defined in the refractor, but the difference was not as much as with the EdgeHD 800. Mars was looking a bit egg-shaped due to incomplete illumination from the Earth’s point of view. Mechanically, with the 700 Mak. mounted on the EVO mount, I noticed that it shook a bit more than with the 8-inch OTA. This is because the 700 Mak. is heavier and longer. The length especially adds a resonating component to the shaking. Still, the long refractor shook more on the CGEM mount, in part because the fine focusing knob on the refractor was not working.
The thought occurred to me that if the 8-inch EdgeHD 800 is DVD quality, then the 7-inch 700 Mak. is in Blu-Ray, and the 6-inch APO triplet is in 4K. As always, the quality of the signal as it relates to seeing is the limiting factor. My suggestion is, if planets are your favorite object to observe and you have money to burn, buy a 6-in APO triplet refractor to have a super-quality instrument that you will always appreciate, and a 5-inch Masutov-Casagrain on a VersaGo II or some such tripod for convenience. If money is a factor, then buy the middle of the heights $1K 700 Mak. and be happy that you can afford such a fine and practical instrument. If you are more into deep-sky objects and astrophotography, you may go with the EdgeHD 800 for the greater light-gathering power. However, a 6-in APO triplet refractor would give amazing widefield views under dark skies.
