Celestron Advanced Series C8SGT

At first blush, the Celestron C8-SGT (Plate 14) does not appear much—if any— different from the LXD75. Ah, but appearances can be deceiving. At nearly the same price, $1,515, the Celestron is arguably a more capable telescope. It does not look that way at first glance, certainly, with its subdued gray tube and black GEM, but some of its characteristics make it more suited for advanced pursuits, such as imaging, than the Meade.

My C8-SGT story starts with a lingering backache. The SGT's CG5 GEM did not cause this complaint; the culprit was my Celestron Ultima C8, an optically splendid old-school manual fork-mount SCT. I had always loved the U8 for its wonderful

Plate 14. (C8 SGT) Celestron C8-SGT German mount SCT. Credit: Image courtesy of Celestron.

views, and when it came time for a recent star party, I decided I would take the Ultima with me rather than my go-to CAT, a large and heavy Celestron NexStar 11 GPS. The images delivered by the U8 are, to put it mildly, as good as any I have seen in any 8-inch telescope of any design over 40 years of observing.

Unfortunately, good images are not everything. It had been a while since I had used the Ultima or any noncomputerized fork scope (I do subject my freshman astronomy students to them), and I had forgotten what using an SCT on a wedge meant. It meant that all too frequently I was contorting my body into a pretzel shape, both to find objects and to view them. That was okay when I was 30. It was still okay when I was 40. But at 50? I was laid up for a solid week.

After I returned from the star party, I determined that I still had a place in my telescope stable for an 8-inch CAT, which is superportable but with plenty of viewing horsepower for all types of sky objects. I decided no more crouching behind the non-go-to Ultima. What to do? Pony up for a new Meade or Celestron 8-inch? It seemed a waste to let those wonderful Ultima optics go idle. What if I removed the tube, the OTA, from the Ultima's fork mount (a simple operation involving removing four screws) and put it on the Advanced Series' CG5 GEM (which was available without an optical tube)? I would make my own C8-SGT and see what the mount would do.

Three years later, I am still happily using my "custom" C8-SGT. When I received the mount and placed my Ultima 8 OTA on it (via a third-party dovetail rail), I was given an education in what is possible go-to mountwise for relatively few dollars in this new century. I had expected a flimsy aluminum tripod. What I received was a hefty tubular steel affair with 2-inch diameter legs. The mount head itself was fairly well finished and seemed larger and sturdier than it looked in the pictures. The computer? The mount was equipped with the same HC used on my much more expensive NS11 GPS (albeit loaded with the different software required to run a GEM).

The proof is on the observing field, however, and I soon had the scope running through its alignment. The go-to alignment is similar to that of the LXD75 in that it defaults to a two-star alignment. When the alignment is complete, though, the mount gives the option of adding up to four cone-alignment stars, which makes the C8-SGT's CG5 mount surprisingly accurate. I was amazed, in fact, at how good the GEM's go-to accuracy was. On my first evening with the SGT, I punched galaxy M63 into the HC without expecting much. The mount began moving, appearing to position itself in the correct general area of the Sunflower Galaxy. Still, I expected nothing more than an anonymous field star or two when I put my eye to the eyepiece. Surprise! There was the dim ghost of a spiral galaxy staring back at me. Okay, Mr. Smarty Pants, give me M64. Boom! The Blackeye Galaxy was centered. M53! That glittering star ball was almost perfectly positioned. I was so excited I ran into the house, grabbed my wife, and literally dragged her into the backyard for a look. I would have thought that after my many years of observing with lots of fancy equipment it would be impossible for a sub-thousand-dollar mount to excite me, but it did. The CG5 just worked well and simply.

I later found out that the CG5 was even better than I thought. I could even take pictures with it. I am not exactly an advanced astrophotographer, even after 40 years of trying, but I do like to take the occasional deep sky snapshot. The CG5 has more than enabled me to do that. I have taken scads of attractive (to me) color charge-coupled device images with the Meade DSI (Deep Space Imager) color imager and my homemade C8-SGT. All these have been unguided 30-second to 1-minute exposures. The gears on the CG5 are good enough to usually deliver nice round stars when the scope is well balanced. It is also not difficult to achieve a polar alignment good enough for imaging. The hand control includes a polar alignment utility that actually makes that task easy.

But, this was with my Ultima 8 OTA riding on the CG5. What will images be like in a genuine Celestron SGT-8? Probably, they will be better than in the Ultima 8/CG5 combination. The Ultima is a fine OTA, but it is unlikely the nice old CAT would be able to compete with a just-produced C8 with Celestron's high-performance XLT coatings, their analog of Meade's UHTC. The new OTA correctors pass more light, and their mirrors reflect more. Images in a current C8 are noticeably brighter than those in an old Ultima. What one thing is better with the older OTA? The focus action on current Celestrons is smooth but not quite as buttery smooth and easy as on the old scope. On the other hand, some users have commented that the focus on the Ultima OTA is "too easy." Maybe it depends on what you are used to. The glossy black Ultima OTA is certainly classier looking than the gray finishes of the new C8 OTAs. Of course, all CATs are black in the dark.

What is there not to like about the Celestron? Sure, there is always something not to like with any telescope. The Celestron NexStar HC is very similar to the Meade Autostar but has one big strike against it for imagers: It lacks PEC. There is no way of recording a guiding run to minimize periodic error. That is not a fatal lack for astroimagers, however. The periodic error on the CG5 is smooth and regular and easily guided out manually with button pushes or automatically with a guide camera. The mount features an ST4-compatible autoguider port, and autoguiding programs are able to deliver round stars in exposures as long as 15 minutes at f/6.3 or f/3.3 (via focal reducers and reducer/correctors described in Chapter 6), which are the longest exposures you will probably need to do.

Are there other complaints? Let us face it, the CG5 GEM is not the rock of Gibraltar, and while slightly heftier than the LXD75, it is not in another class. It is very stable with the C8 OTA except on windy nights, and even then visual observing is not much affected. Imaging is affected and is simply not practical under windy conditions. A set of Celestron's vibration reduction pads (Chapter 6) can at least reduce vibrations caused by wind, if not completely eliminate them. The noise produced by the CG5 mount while moving to targets at its maximum go-to rate is slightly less than that of the LXD75, but not much. If the neighbors are easily awakened, do not do too much go-to slewing in the backyard late at night.

The accessories included with the C8-SGT include a 12-volt DC power cable (there is no option for onboard batteries; this mount needs lots of current to operate reliably), a too-small 6 X 30 mm finder, a decent 25-mm Plossl eyepiece, and a CD containing TheSky home planetarium software. For observers strapped for cash, the C8-SGT is available without XLT coatings for a slightly lower price (not recommended).

All in all, the quality and utility of the Celestron C8-SGT and its CG5 mount are excellent. Yes, there are some nits to pick, but the mount is adequate. A more expensive, heavier GEM might do things a little better or more easily, but the C8-SGT gets the job done.

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