The Celestron 8" Schmidt Cassegrain Telescope (SCT) may be the most mature optical product in production. Yep, Period. The CPC 800 combines this optical tube with a third generation computer driven geared mount. This is perhaps interesting itself because this is the first ground-up Goto telescope system with this level of system design experience behind it, and after using one, it is pretty easy to conclude it is perhaps perfect. And this makes a difference in what form the system has taken. The annoying oversights have been weeded out in previous variants. This models follows on the heels of the mighty
NexStar 8 GPS , which not only was the first to have GPS location and time referencing, but it has shown it stands the test of time and continues to function reliably with continuing use. More general information on choosing a telescope is in my article,
Picking a Telescope.
Background
The Celestron C8 is one of the products of the modern era of technology integration. It is a hybrid design with a glass corrector plate in the front combined with mirrors to form the most compact optical tube compared to either its diameter or forcal length thus far developed. It is combined with extreme focal range flexibility, so focusing eyepieces, cameras, binocular viewers, or even spectrographs is within the capability of these telescopes.
And because of this, they practically swept away the long tube refractors and Newtonians which dominated amateur astronomy when they appeared in 1970. The net result has been a sort of democratization of the hobby as telescopes capable of serious observation work were put in the hands of amateurs.
The first C8 was mounted on a tripod with a fork mount and tracked the stars with a simple clock drive. The formula for this telescope met a lot of needs in a compact package, and variants of this design such as the
Celestar 8, stayed in production through 2000.
The first few attempts at computerizing these original mounts were little more than ways to indicate the current pointing. To make the mount move to an observing target, the user would find it on a computer, then move the telescope until on-screen pointers came to the object. While this was acceptable for a permanent observatory, it was otherwise not much use.
The ability to actually drive to an observing target needed a new telescope, and that was the
Ultima 2000. This was fated to be a lone example, and it was relatively expensive at around $2,800, despite being loaded for bear. This telescope came with one other neat trick- it could guide while mounted with the forks straight on the tripod and no equatorial wedge.
The Ultima 2000 came with another interesting feature in the optical tube; Fastar compatibility- this was a photography only system where the secondary mirror could come out of the secondary and a special lens assembly could attach a camera where it could operate at f/2, an incredibly fast optical system.
The successor to the Ultima 2000 was the
NexStar 8 GPS . This time the telescope was part of a complete product line of computer guided telescopes. It had larger siblings such as the
NexStar 11 GPS and NexStar 9.25 as well as smaller variants such as the
NexStar 5i and even smaller units such as the
NexStar 80GT. And this larger set of products came with cost savings of over $800, while the NexStar GPS series had faster as well as carbon fiber barrels in the optical tube to reduce thermal shrinkage, which changes focus as the telescope cools during the night.
But, there was one serious problem: Meade had a patent on the method the NexStars were using for alignment. They were sued, and settled where a royalty had to be paid. Fortunately for the rest of this, this pushed their hand to see if a better way could be found.
Description and Usage
The Celestron CPC 800 has a lot of clear similarities to the previous
NexStar 8 GPS . This product may be best understood as a consideration of its changes from that one, so I am going to focus on that. More background is in the writeup on the earlier telescope.
First, the optical tube has four changes.
-First, the composite barrel has been deleted and the design returned to the original aluminum barrel. There is (no joke) a worldwide shortage of carbon fiber, so I expect this had become expensive, when the actual benefit is very subtle.
-The second change is to the optics themselves- they incorporate a new coating and glass system called Starbright XLT, which has a white glass corrector and more modern optical coatings to improve transmission.
-The third change to them seems to be mostly stylistic- the castings for the front cell ring and the back bucket have a slightly different shape where the front ring has a sort of wide bevel in it and the rear cell has a triangular raised area on the outside.
-The last change is the Fastar removable secondary has been deleted. Note, this has largely been handed over to Starizona, www.starizona.com, who sells the related Hyperstar lens system which takes one of these to f/1.8 for photography. They are able to swap the secondary assembly for this, so you can still get this capability if you want it.
Optically, the scope I used would have to rate as "OK." The collimation was slightly off, and as I have mentioned before, these are sensitive to that. So, it only showed four stars on the trapezium, and in moments of good seeing, the fifth. With that said, the result appears to confirm Celestron's scopes are fairly uniform these days, and that is good news indeed. The difference from the optical coatings isn't something directly visible in most cases, since we are talking about maybe a 4% difference in net light throughput. You may be able to see it in the dark skies of the countryside if you had both scopes next to each other.
The mount and tripod has the bulk of the changes to this scope, where the worst problems from the previous telescopes have been addressed.
-The tripod is now stainless steel, and the attachment bolts for the telescope are now captive, so installation is a lot easier (plop scope on, turn until you can get one of the bolts started- do not do more than start it for one turn until the other two are started, then tighten them all).
-The spreader for the tripod les now has some ability to be a tray, and deletes the older and weaker spider type spreader. there is still an annoying screw to tighten to operate the tripod.
-The mount base and arm have a new type of clutch- instead of sliding levers, then have knobs with three ridges to turn them and lock and unlock. Note, the base knob needs to be tight to turn the base when attaching to the tripod since the entire base moves with the forks, where the older NexStar GPS units have a lower non-roating section.
-All of the plugs are now on the rotating section, so the power cord wraps as the unit moves and the switch is on top of the drive base. The base is now light colored, so these details are visible in the dark, and the power switch has a red indicator light lit when on.
-The NexStar hand controller now resides in a side cradle where it is visible from where you look into the scope. This is a real improvement over the previous model, where the side "Phone cradle" hid the display and was difficult to use in the dark.
The list of what isn't different is basically everything else. The technique for lifting the scope, which works quite well on the NexStar GPS, has been retained, and the drive and motor systems are so similar between the two models that Celestron offers a version of this one's controller as an upgrade to the original NexStar GPS series. The main structure is also similar, with all load-bearing components made of aluminum and plastic restricted to the covers to protect the electronics.
To use this telescope, the startup sequence has it automatically go to a GPS alignment. Unlike the dance the previous NexStar does to get to a lousy approximation of where an internally chosen first star will be found, this telescope simply asks to be moved onto three alignment stars. Look up and pick three stars across the sky, point to them, get them centered in the eyepice, and tell it to align. At the end of this, it will need to think as it works to resolve the locations with internal maps. When it has done this, it will announce Align Success. At this point, you can query it to see what three objects it thinks it aligned on, and if these are wrong, you can try again. But in four tries, including one where I had it use Saturn as a star, it did well. More importantly, with three stars chosen from across the sky, the alignment was extremely good compared to the older NexStar, where only by using a
reticle eyepiece can get this level of accuracy.
What is interesting is how past this point, the telescope is actually very similar in behavior to the older NexStar. Obviously this isn't a coincidence, but my point is the usage is essentially transparent. The difference I would point to is the pointing accuracy of the new NexStar controller is clearly superior to the original NexStar GPS series, to the point where I am seriously considering the upgrade for my older scope.
Like all C8 series telescopes, this one is a lot of telescope, and Celestron has really done their level best to put together a package which is about all the telescope a person could need. All of the SCT compatible accessories are immediately compatible with these scopes. The native focal ratio of f/10 will work well on planets and smaller objects, and the
f/6.3 focal reducer immediately opens up the field of view.
Make sure you check your collimation, then go enjoy the night sky. The best setups for a home user will probably be where you can put this scope on a Jim's Mobile Wheelie Bar and roll it in and out of the house through a sliding glass door. This will get you outside, and get the scope used they way it should be. If you are in a situation where the scope has to be carried over steps to go in and out (like me), that will interfere with use since it is a much slower and more difficult process to move it that way.
Another benefit of a rolling setup is some of the more difficullt to use accessories, such as the
Equatorial Wedge can be installed once and left in place. And, if you are looking to attach cameras or smaller scopes, like the
AT-66ED 66mm refractor, by
Piggybacking you won't have to make and break the connection every time the scope moves.
Conclusion
The Celestron CPC 800 is a lot of telescope, and it is in a very user-friendly package. This design is extremely mature, and the "Gotcha" faults of a new product simply are not part of this picture. A lot of specialty telescopes like small refractors get a lot of attention because they are slick looking, and do a good job for their size. But at the end of the day, an 8" SCT is simply at higher level of capability. Given that current offerings by Celestron have these available at a little under $1900 for a turn-key highly capable observing system, they really are the best value for a telescope there is.
