Reviewed by Brent Hutto
My first telescope was a little 60mm f/13 refractor on a shaky az-el tripod mount. It turned out to be surprisingly useful for lunar observing but was limited to a magnification of around 114 (with a 7mm UO Orthoscopic eyepiece). But it met the goals for which it was purchased and cost only $89 for the telescope and $57 for the 7mm eyepiece. My next goal was to observe transits and shadows of the Galilean satellites of Jupiter. For that purpose, I chose a 6″ f/8 Dob. With the same 7mm eyepiece it produces a magnification of 174, which in my opinion is just barely enough to see detail on the Jovian surface (depending on opposition). It also provided much higher-resolution views of the lunar surface, although I never obtained a shorter focal-length eyepiece to maximize its lunar performance. The main limitations of that Newtonian telescope were its single-stalk diagonal holder, which made perfect collimation impossible and produced a major-league diffraction spike, and its lack of an RA drive. This latter drawback made sketching what I saw at the eyepiece frustrating and ultimately not worth the trouble.
In my third year of on-again, off-again pursuit of the skywatching hobby I decided that I wouldn’t really enjoy observing unless I could learn to sketch what I see. And I probably wouldn’t stick to sketching unless I have a motor-driven telescope. So after examining many competing options, I made what I consider a major expenditure and purchased a fork-mounted 8″ SCT. After a couple weeks of using the new telescope, it seems that my decision to “Don’t Fear the Fork” was the correct one. People presume there to be optical and mechanical limitations of mass-produced Schmidt-Cassegrain telescopes and their fork/tripod mountings, which is almost certainly true. In practice, though, being able to set up a telescope in five minutes and sit comfortably at the eyepiece while the RA drive keeps a planet in view indefinitely is quite a luxury. And when the telescope is clean, cool and collimated (the 3 C’s), that 8″ of aperture allows bright, large image scale, high-resolution views of the lunar surface, Jupiter or Saturn. Ultimately, choosing a telescope is not a competitive exercise (at least to me it’s not) and the proper question is “Good Enough?” rather than “Better Than?”. And so far the answer to “Good Enough?” is “You Betcha!”.
There are two manufacturers of entry-level 8″ SCT’s, Meade and Celestron. Rather than belabor the (mostly minuscule) differences between those brands and the different models each offers, let me just say that I chose Celestron. In particular, I chose the Celestar 8 Special Edition from Astronomics in Norman, OK. That biggest difference in the C8SE and the usual Celestar 8 is a heavier tripod and separate EQ wedge rather than the Wedgepod. Since my intended usage was high-magnification lunar and planetary viewing, I felt that the lighter and admittedly more convenient Wedgepod was not a good choice. The C8SE also includes a 9×50 finder scope, a Celestron 10mm Ploessl eyepiece, AC and DC power adapters and a few other freebies. The total cost to me, including shipping, of the C8SE package along with a passive dew shield was $1,400. That is about $200 more than a standard Celestar 8/Wedgepod configuration. It was shipped the day after I ordered it, as promised, and arrived at my door three days after that, right on schedule per UPS’s web site.
When I first looked at the boxes delivered by the UPS person, I thought there was a mistake. Right on the end-flap of one of the boxes was an orange-and-white Celestron label which said “Wedgepod”. However, I noticed that someone had written with a Sharpie marker “Tripod” on the label. As it turns out, there was a heavy-duty tripod and an EQ wedge in the box, no problem. As it turned out, there was one surprise inside when I opened the rest of the boxes. I had ordered a Televue 1 1/4″ mirror star diagonal after hearing many horror stories about the prism diagonals that Celestron and Meade supply as standard equipment. Even though I had asked the Astronomics order-taker to double check the availability of the diagonal, it turned out that the shelf and the inventory computer did not agree. The diagonal was back-ordered and would be unavailable for several weeks. A quick check of the supplied prism star diagonal with my Orion collimating sight tube showed that the prism was off-center and not at a 45-degree angle. I took it apart and after re-assembling it in every possible configuration did find one arrangement that resulted in a good 45-degree angle. But there was still a bit of vignetting that no amount of fiddling could remove. So I called Pocono Mountain Optics the next day and ordered a Lumicon mirror diagonal, which I received a few days later. In the mean time, the prism unit seemed to work well enough for my initial period of getting used to the telescope.
One concern that I had obsessed on while awaiting delivery of my SCT was the difficulty of making fine enough movements in declination and right ascension. There are times when observing the Moon calls for magnifications much greater than 200, hugely amplifying small motions of the telescope. Reviewing the SCT-User mailing list archives and corresponding with Rod Mollise convinced me that the declination fine adjustment on the C8SE would probably work well for my purposes. But the fine RA adjustment is coarser and has the added complication of a locking lever than must be engaged and disengaged when overriding the drive for manual RA motion. At Rod’s suggestion, I ordered a $60 hand control unit which plugs into the base of the telescope and commands the motor to move at 2x or 6x sidereal speed either backward or forward for moving the target object around in the eyepiece field. It will also perform the same function in declination with the addition of a $120 electric motor.
After using the telescope both with and without the hand control, in retrospect I wouldn’t have spent the extra $60 on the hand control box. It turns out that with a deft touch you can find a sweet spot where the RA locking lever just barely engages the RA drive or just barely disengages it for fine manual RA adjustment. If used carefully, this avoids nudging the telescope away from the desired heading when re-engaging the drive after a manual movement. And on the other hand, there is sufficient backlash in the RA axis that 2x or especially the 6x slewing is often followed by unwanted drift until the drive motor takes the slack out of the system and resumes smooth motion. It may be that balancing the OTA better would minimize this problem and make the hand controller a better option. There is also considerable play in the manual declination control. When the dec knob is being turned in one direction and is then reversed, there is often 1/10 of a rotation or so before the OTA actually moves in the opposite direction. Somehow I doubt that spending money on the electric declination motor would be the solution to the problem, though.
At least four other issues were on my mind as I began using the telescope: Collimation, Dew, Image Shift during Focusing and Portability/Setup. It is both a curse and a blessing nowadays to have access to the huge volume of telescope-related discussion available through the Internet. On the one hand, you can easily obsess on any number of potential “gotchas” that might afflict your new, expensive toy. On the other hand, ideas for solving these same “gotchas” are readily available through the same medium. My concern about collimation illustrates this point. If you read much about SCT’s you’ll come to the (correct) conclusion that a well-collimated SCT results in a happy SCT owner and vice versa, so it was with some trepidation that I attempted for the first time to collimate the C8SE. I didn’t have any “Bob’s Nobs” and the phillips-head screws used by Celestron were supposed to be questionable. On the other hand, I had printed out a chart that showed which screw to turn depending on what you saw when you looked at a defocused bright star. What sounds like a long story turns out to be rather short. I defocused Vega at 290x with my 7mm ortho directly in the visual back (no diagonal). The bright center of the diffraction rings was offset upward and to the left. I tightened the screw suggested by the instructions and no change. So I put it back and loosened the other two screws about 1/8 of turn. Collimation perfect, end of story. And the secret to the phillips screws is to use a brand-new screwdriver rather than a worn-out one and to do the adjustment while standing in front of the telescope rather than trying to reach around while looking through the eyepiece – that’s where the cheat sheet showing which screw to turn pays off.
Dew has not been a problem so far. I use a flexible plastic dew shield with “Celestron” written on it and so far the telescope has survived sitting out for 5 hours during which the temperature dropped 20 degrees. However, right now we are having some very dry autumn weather. I have little doubt that come spring and summer I’ll have to take additional precautions against the dreaded condensation. Image shift during focusing doesn’t seem to be a problem for visual use even at high magnifications. Normally, it is not noticeable below about 300x but occasionally it will make an unexpected big jump. This only seems to happen when I’ve been moving the focus knob back and forth over a small range repeatedly. I think the focuser lubrication gets bunched up and causes an unwanted shift. When this happens, I just run the focuser in about 15 turns, out about 30 turns and then back to where I started. That makes the problem go away for quite a while.
Portability is not too hard to deal with and setup time is very short. If I had to take the OTA and drive off the wedge every time I can see where that would get tedious. However, the whole assembly at 51 pounds is just within my no-backache range. Now if I had to bend over to pick up something that heavy, I’d be courting trouble. However, I can grasp the top of the tripod with my knees bent very slightly and then stand straight up so I lift and carry the tripod, wedge and OTA anywhere in the house or yard with my back perfectly straight. Ten pounds heavier would be tough and if the tripod legs were any wider they wouldn’t fit through some doors. The heavy tripod I have has a spreader that keeps the legs from folding unless you take the whole assembly apart. So it’s a close fit but it works for me.
Optically, I have no complaints with this telescope. During one evening of incredible seeing I was able to use the highest magnification I had available (7mm ortho plus 2x barlow for 580x) on the Moon. With an exit pupil of one-third millimeter, the image was dim and I did notice that some low-contrast features started getting washed out. But the peaks and shadows I was observing had more detail at 580x than they had at 400x which in turn was more than at 290x and so forth. Now admittedly the Moon is a special case that can soak up magnification like no other astronomical object. But if my SCT’s optics were awful, I don’t think there would have been any detail available at such ridiculous magnifications, even on the lunar surface. With more typical seeing conditions, 290x or so seems to work very well on the Moon, especially with an orange filter. Jupiter shows more surface detail at 204x than at 290x, although Saturn’s rings and their Cassini Division do fine at 290x. At 163x the Moon, Jupiter or Saturn are almost always bright and sharp but at that image scale not much detail is visible, at least with my eyes.
As an additional bonus, the telescope is usable for photography of the Moon or, surprisingly, of terrestrial objects. I bought a Celestron T-adapter with integral 2x barlow along with my telescope, almost on a lark. However, prime-focus full-moon photos (with the barlow removed) are very nice. And pictures of birds on our backyard feeder taken from 75 feet away show an amazing amount of detail, although focusing is tricky since the viewfinder image is quite dim. Photography is not something I intend to pursue as its own hobby. But the option of playing around is definitely worth the $43 I spent on the T-adapter/barlow. My next purchase will be some additional eyepieces. Right now, even using the 2x barlow, only a few magnifications are available to me: 81x (26mm Ploessl), 162x (26mm Ploessl + 2x Barlow), 204x (10mm Ploessl), 290x (7mm Ortho), 408x( 10mm Ploessl + 2x Barlow) and 580x (7mm Ortho + 2x Barlow). Jupiter, for instance, would benefit from something in between 204x and 290x under most seeing conditions. And I think that something in the 320x-350x range would be useful on the lunar surface most nights. But with the addition of a couple of eyepieces and perhaps some kind of dew heater arrangement come spring time, this setup will let me spend hours and hours observing and sketching the Moon and bright planets. I’m looking forward to the 2001 apparition of Mars, as well. To anyone with observing goals similar to my own, I would unreservedly recommend an 8″ SCT as a valid approach to pursuing those goals.© 2000 by Brent Hutto