Archive for September 20th, 2020

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New scope: Celestron NexStar 8SE

September 20, 2020

London looking through the scope the first evening, when I had it on the AZ-4. His 60mm Meade refractor waits in the background.

Welp, I finally did it. I’ve been low-key lusting after one of these scopes for a few years now. Between 2007 and now, I’ve owned reflectors from 70mm to 300mm, refractors from 50mm to 102mm, and Maks from 60mm to 127mm, but I’ve never had a Schmidt-Cassegrain, and I’ve never had a GoTo scope. I figured it was time to rectify both of those omissions. What tipped my hand was the planets: I’ve had great fun these last few weeks observing Jupiter and Saturn almost every evening, and Mars on many evenings, as we speed toward opposition with the Red Planet in mid-October. Yes, the Apex 127 and the XT10 both do great on planets, but after a while I get tired of nudging them along, especially at high power. Also, the XT10 weighs about 55 lbs all set up and kitted out, and some evenings I wuss out. It will be nice to have something between the 5-inch Mak and the 10-inch Dob for those times when I want a little more oomph and a little less hassle.

If the NexStar 8SE is actually less hassle–I’m new to computerized scopes, or indeed even to motorized scopes, and my first night getting the whole system set up was not without some frustration. But I’m getting ahead of myself.

The first point in this saga is that the NexStar 8SE, like almost all NexStar scopes, and like almost all computerized scopes, and in fact like almost all scopes period, is almost completely sold out right now, from sea to shining sea. This is apparently less about the pandemic disrupting supply lines and more about a completely bonkers demand for telescopes during the era of COVID. A lot of people are looking for hobbies while they are stuck at home, and sales of astronomical gear are, well, sky-high, at least according to the vendors I’ve heard from via email or on Cloudy Nights. So it took some doing to find one. I usually prefer to support friendly local and not-so-local telescope stores like Oceanside Photo and Telescope, Woodland Hills Camera & Telescopes, Astronomics, and Orion, but none of them had the scope in stock when I was looking. Turns out, Amazon had a few, so I put in an order. Aaaaand…nothing. More than a week after I placed the order, the scope still hadn’t shipped, and there was no sign that it was going to do so anytime soon.

During the unboxing. Each big component is sandwiched in styrofoam or ethofoam, inside its own box, and all of them are in two bigger boxes. The square vacuity at the lower right held the box for accessories. Note the ruler sitting on the OTA–this is a big scope, in a big package.

Frequent commentor, sometime observing buddy, and telescope-purchase instigator Doug Rennie came to the rescue, with an AmazonSmile link to NexStar 8SEs that were said to be shipping in just a few days. I canceled the original order and tried again using Doug’s link (which is here — apparently the scope is still in stock). The scope arrived in just a couple of days, which is only surprising because the estimated delivery time was more like five days. It arrived in a big box: 3.5 feet x 2 feet x 12.5 inches.

On the day that the scope arrived, I had no way to power it. I had been planning to order a rechargeable battery pack (this one), but hadn’t gotten around to it; we were out of suitable alkaline batteries at the house; Vicki had the car to work a forensic case so I couldn’t drive to the store; and London and I were still sunburned from a trip to the beach the previous weekend so we didn’t want to walk to a store. I took a page from Uncle Rod (this post and this one) and put the C8 OTA on the SkyWatcher-branded Synta AZ-4 alt-az mount I got back when. The result looks goofy as heck but it works. At 17″ long and 9″ in diameter, the C8 is a voluminous scope, but it’s mostly air, and the OTA is not much heavier than the Apex 127/SV50 combo that I use on the AZ-4 all the time.

C8 OTA on the left, Apex 127 with rings on the right.

Here I hit a snag. The NexStar mount is left-handed, the AZ-4 is right-handed, so the C8 tube went on upside-down. That put the focuser knob above the visual back, diagonal, and eyepiece, rather than below, which was weird but not a deal-breaker. It also put the finder mount–a little Picatinny rail for the included red-dot finder–below the scope’s equator instead of above it. (I had the same problem with the Apex 127 back in the day, as discussed in this post.) I figured heck with it, I’d get by just sighting down the tube. I do it all the time with my other scopes, and it works okay.

Correction: I do it all the time with my other non-Cassegrain scopes, and it works okay because they have short focal lengths and wide fields of view. The C8 has a focal length of 2032mm and a max field of view of a little less than 1 degree. Getting the scope pointed at anything without a finder involved a tremendous amount of faffing about, like 5 to 10 minutes per object. It would have been way simpler to just mount the RDF and crouch down to use it. But like a bloody-minded fool, I persevered without, and managed to observe the following objects the first night out:

  • Jupiter – even at just 63x in not-great seeing, I caught the Great Red Spot easily in direct vision.
  • Saturn – also at 63x, immediately got 4 moons. I’m sure more would be possible on a night with better seeing. I ran the magnification up a bit, but didn’t see any more. That’s how it goes when the seeing is bad.
  • Moon – holy light-collecting area, Batman! At low power, with the entire just-past-full moon in the FOV, I heard a sizzling sound and a beam of moonlight shot out the back of my head. I ran the power up to 169x and saw subtle features in the maria that I’d never seen before, especially inside flooded craters on the margin of Mare Fecunditatis. Focus on the C8 was surprisingly snappy for a non-refractor–one second an object would be out of focus, then BAM, it was in, no question. I decided a star test was in order. But first, on the way to the pole:
  • Mars – brilliant. Even at 81x with the included 25mm Plossl, I could see a wealth of detail on the surface, including the dark triangle of Syrtis Major.
  • Polaris – used this for a star test. Happily, the collimation appears to be dead nuts on. The star test looks excellent. I hauled out a copy of Suiter’s book, Star-Testing Astronomical Telescopes, which is on loan from a fellow club member. Any problems with the optics are below the threshold of my ability to diagnose. This is consistent with the fine details and low-contrast features I was picking up on other targets.
  • Vega – I just used this to get on target at Epsilon Lyrae, but I was happy to see no chromatic aberration. I did catch just the faintest whiff of greenish-yellow on the limb of the moon, but I can’t be sure that wasn’t in the eyepiece. Long planetary and lunar sessions with the Apex 127 these past few weeks have shown me that eyepiece CA is real, and varies a lot between makes and models.
  • Epsilon Lyrae – by now the seeing had turned to crap again, at least in the west. I only ran up to 169x and the stars were still too shimmery to “black-line” split, but I was happy to see that they were elongated into little 8s at 81x, which makes me think this scope will split the Double-Double below 100x on a still night. That’s not any huge achievement, but it’s nice to know the scope is performing within expectations.

In sum, the scope is optically great. I’ve been pretty lucky with most of my scopes, but I’ve had a couple of stinkers, so it’s nice when they turn out better-than-expected, which this one certainly did.

In fact, it was a little anxiety-inducing. I really, really wanted the mount to work, too, so I’d have no reason to return the package and lose such a nice OTA. Yesterday (Thursday) I had to run some errands anyway, so I picked up some batteries. By this time I had a rechargeable external battery pack on the way, but not yet in. So I murdered some AAs to try out the mount.

The accessories that come with the NexStar 8SE. Clockwise from the upper right: a bubble level for leveling the tripod before you put on the mount and telescope; a 25mm Plossl (of course!); mirror star diagonal; and the hated red dot finder (RDF).

First thing: you really, really need a finder to get the scope aligned for GoTo. Which means the finder needs to be aligned to the scope, and I foolishly had not done that during the day. Have I ever said how much I hate, hate, hate red dot finders? My first accessory purchase for this scope, after the external battery pack, was a 9×50 RACI, again from Doug Rennie, who had gotten one for his NexStar 6SE but wasn’t using it. Anyway, after some faffing about I got the RDF on and aligned. Did a rough alignment on some distant leaves, then got it dialed in on Capella.

I had just watched a video Doug had sent on the Auto 2-Star alignment (this one), so I did that, starting with Capella. The suggested second star was Vega, which was still visible in the west. Got the alignment dialed in on Vega, then I was off and running.

First object I tried was M27. I couldn’t see a darned thing, BUT it was going down into the light dome over LA, and fighting the light of the nearly-full moon, so…who knows. After that I punched in Mars, and after the scope stopped slewing, Barsoom was in the eyepiece and looking good. Pleiades, ditto, although they spilled well beyond the sub-1-degree field of view. M34, ditto. Neptune, ditto, a tiny ball of blue floating out in the black. Then the moon, and like every one of the others, it was just about centered in the eyepiece. These objects were reasonably well-distributed over the sky, so I was pretty happy with the mount’s ability to get the scope on target. I let the scope just track the moon for a few minutes while I took some notes.

One thing–I had left the tripod legs collapsed for max stability, but even sitting down that put the eyepiece about 7-8″ lower than it could have been, and punishingly low on some high targets. I figured I’d elevate the scope a little more in future sessions. To figure out how much I’d need to raise the tripod, I punched in Aldebaran to get a low-in-the-sky target, and the scope slewed right to it. I spent a few minutes using the hand control to drive around the Hyades, looking for double stars, then stopped to write some more notes. Have I mentioned that I’m including more double stars in my observing these days? Blame the Astronomical League’s Double Star and Binocular Double Star observing programs, for acquainting me with so many fetching targets.

At this point the mount had been on for about an hour. I tried for the double star Eta Cassiopeia, and the scope drove to Cass, but not to the star. I wondered if the batteries were dying–apparently GoTos lose their minds as the power runs out–so I punched in Polaris, hoping to get one last target, but the scope slewed off to the east, in completely the wrong direction, and then stopped moving entirely. I flipped the power switch off and put everything away. The scope ran for a little over an hour on the AAs, which is in line with what others have reported. And also a fairly expensive session!

The NexStar 8SE set up just inside the garage, looking south over the car for some alignment and tracking testing.

So, the OTA was optically great, and the mount worked, did GoTo, and tracked objects. The Talentcell battery pack (this one) arrived the day after the AA-powered session. What I wanted to do was set up in the driveway for a long planetary session, to see how the mount and battery pack work during extended tracking, and to take the whole rig up the mountain soon to see how it would work on a multiple-hour session under darker skies. Unfortunately by this time ash from the wildfires was raining from the sky, and ash is hell on telescope optics, so both the driveway and Mount Baldy were out. Still, I was desperate to know how the whole rig would work together, so I set the scope up inside my garage, which has a south-facing door, and did some tests in the southern sky. After doing a two-star align on Fomalhaut and Nunki, the system was putting objects near the center of the FOV every time. I also tried a single-object solar system align on Jupiter, and that was good enough put objects somewhere in the FOV of a low-power eyepiece, and to track for 20 minutes or so, but definitely not as good as the two-star align.

Why was I pushing to get this scope and mount tested when conditions were so crappy? That will be revealed in the next post.