Well, I’ve finally done it! I’ve finally bought my long sought after Celestron 9.25-inch optical tube assembly (OTA). I had been very patient, waiting and waiting for a used one to come up for sale at a reasonable price with the newer Starbright XLT coatings, as they have about 10-15% greater light transmission than the ones with just the older Starbright coatings.
It just got here on Saturday, along with the usual and customary clouds. Man, it is a gorgeous thing! Here is the unboxing ceremony:
And here’s where it’ll be spending all of its time, on its own mount, the Orion Sirius Pro AZ/EQ-G:
Mount problems
I learned a couple of things very quickly in using the scope and mount together. First that I should have some sort of counterweight on the other side of the scope. This is just to make sure it’s a little better balanced, so there’s less of a chance of it tipping over. No, don’t worry, it didn’t tip over – it’s just a precaution. I tried pushing it over – the mount is pretty dang solid.
The other thing I learned is that I gotta extend these tripod legs out. All the way out. I’m not used to doing that, as with my lighter weight SLT mount, I keep the legs only halfway extended to keep the center of gravity lower, to keep it more stable. The C9.25 and Sirius together seem so hulking and large sitting in my living room. But when you point the scope at something elevated in the sky, that eyepiece gets awful low, and this aging body ain’t so good at getting up when the seat is only 6 inches off the ground. The Sirius Pro is a very heavy, beefy mount, so extending the legs out all the way will raise the scope up enough to help my knees from not having to get down so low. Observing while practically sitting on the frozen ground is just no fun and doesn’t lend itself to observing for extended periods.
This was my first full up use of the mount; I had previously only tested it out relatively briefly when I bought it in May with the Mak to make sure that it worked. And it worked well then. But with the C9.25 on it, the mount only worked so-so; it was consistently off when I told the mount to slew to Messiers, even though I had done a good alignment on two stars that were fairly well separated. It was consistently off by well over a degree in altitude and about half as much in azimuth. With only a 0.69-degree maximum field of view with the 68-degree Explore Scientific 24mm, that meant a lot of hunting for the object after the mount was done slewing.
And it wasn’t because the mount wasn’t level – I had made sure to level it fairly well before starting. Although that shouldn’t make any difference, because once you’ve aligned on two stars, how well the mount is levelled shouldn’t make any difference in Alt-Az mode.
One of the drawbacks of the Sirius mount – or more to the point, the software controlling the mount – is the inability to realign. With the NexStar handset/software, when the mount slews to an object, if it’s off, you can correct it. You can find the object, center it, and then tell the scope, in effect, “No, you were off – the object is here.” You press the Align button, and now your alignment is more accurate. With the Sirius, what you get is what you get. If it’s off, you can do another alignment with stars closer to the object you’re looking for – if it offers you the choice of closer stars in the selection menu. That helped, but the further away from the alignment stars I went, the more inaccurate the slew was.
Maybe it didn’t work properly because it needs that counterweight on the other side? I put the 7 1/2 lb. counterweight on when some of the guys on the Facebook astronomy pages wagged their fingers at me that I should do so to keep the mount from being too prone to falling over on the overweighted telescope side. While I was getting it ready to take out, I put the second mount head on it to hold the second scope – which is much lighter than the counterweight. I was intending to mount the Mak and the ‘frac on the other side, but I was so wrapped up with using the new scope that I didn’t get around to mounting the old ones. I’m gonna need to experiment with the mount to see what the problem is.
Focal reducer
At least a partial solution to this will be when the 0.63x focal reducer I bought (used, natch) off of Cloudy Nights arrives. The focal reducer effectively reduces the focal length of the scope by the fractional factor indicated; or you could consider it a percentage. The main result is that the field of view of the scope is wider – and therefore, it will be easier for the scope to put the objects in the field of view. It also flattens the field as well, meaning that the view is less subject to field curvature, a particular type of visual aberration.
The 0.63x FR/FF will reduce the C9.25’s 2350mm focal length down to 1480mm, just a hair shorter than my Mak’s 1540mm. The result is that with the FR/FF, the magnifications and fields of view I get now on the Mak will effectively be equivalent in the C9.25; I’ll get a tiny smidge wider field of view in the C9.25 with the FR/FF than I can with the Mak.
There is some debate over whether you can use 2-inch accessories (2-inch visual back, which takes the place of the regular 1.25-inch one; 2-inch diagonal; 2-inch eyepieces) combined with the FR/FF to get an even wider field of view in the C9.25. I’ve read arguments on both sides from people whose opinions I respect.
On the negative side, one source says that the combination will result in vignetting, meaning an extreme (50% or more) dropoff in light towards the edge of the field. This means that the extra field of view you get from the wider field eyepiece is effectively lost because it is so difficult to see. On the other hand, someone else has written that the combination will get you to just about 1.5 degrees – wide enough to fit the Pleiades in with a little room to spare.
Eventually, I plan on getting an Explore Scientific AR152, a six-inch achromatic refractor. I want to get it specifically for the very wide field views it can offer – around 2 1/4 to 2 1/2 degrees field of view, depending on the eyepiece I use. Now that’s wide. And it does this while providing 6 inches of clear aperture – which is about the light-gathering equivalent of about 7 1/2 inches of aperture in most other scopes. This is due to light losses from the size of the central obstruction and because of imperfect reflectivity of mirrors (around 91-93% reflectivity for both the primary and the secondary, each). Once I get the AR152, I’ll use the 2-inch diagonal and EPs from it on the C9.25 and, of course, I’ll report back.
Is this a new C9.25?
As I mentioned, I bought this C9.25 OTA used off of Cloudy Nights, at about a one-third discount off the price if it were brand new. (Mmmm, boy does that appeal to the inherent cheapitude in me.) But is this scope really used or not? The seller told me that he had bought it from one of the regular astrovendors and used it about a dozen times. But that’s not what the tale of the tape says.
Not only is there tape closing the box that says “Celestron Quality Assurance”, but there’s also a slip of paper in with the owner’s manual – and an unfilled out registration card! – that says that the item has gone through Quality Assurance. In other words, that this is a refurbished scope. Now that doesn’t necessarily mean that there was something wrong with it that needed to be refurbished, or that it was ever actually “used” in the sense of actually being put on a mount and put under the sky.
Most scopes are returned simply because of buyer’s remorse – that the scope was too expensive, or that the buyer decided they didn’t want the scope in the first place. Other times, scopes are returned because of something incredibly minor – like that the focus knob was stiff, or that there was some minor misalignment of something – anything. And finally, some scopes are returned because there really are major problems with it – a stuck mirror, an incorrectly aligned corrector plate, a crack in the plastic end pieces.
Refurbushing means that a scope is checked from head to toe to make sure that everything is up to spec. And if it’s not, it’s fixed or replaced. With all due respect to the person who sold me this scope, this scope came back to me not only in perfect condition – the scope is flawless, there’s not a mark on it, and it’s clean as a whistle – but it came wrapped up perfectly, as if it were brand new. Look at the second picture, above. I’m one of those people who saves the materials that the scope came with. But to save even the tissue paper the scope was wrapped in? Hell, I ripped the tissue paper just taking it off the scope in my unboxing frenzy! And to save the little yellow “don’t look at the sun” card and drape it over the focuser? Come on!
Mind you, I am not complaining. I am beyond thrilled to get what appears to be brand new scope at one-third off. But it’s a mystery, and it’s hard for me to just let this go. Like Columbo, I need to solve mysteries.
Finally, what you came for – the C9.25 review!
I gotta say, I am liking this scope. First off, it’s sleek, shiny black. It’s also light in a weird way. Even though the tube is 20 lbs., it’s mostly air, and it seems like it’s much lighter than it is. Plus, without the heavy meniscus of the Mak in front, all the weight is in the back. It has a very handy handle in the back, making it easy to maneuver and put on the mount.
I brought the entire rig out to Settler’s Park, a local park in Aurora about half a mile away from my house. (Oh, did I forget to mention? I moved about 8 miles east in October. Which is why there were no blog posts in November.) Like all parks here, it has lights that never turn off at night. However, they’re located only in a small portion in the western part of the park, by the playground. As you go further east into the park, those lights are behind you, leaving a wide open view of the full eastern and southern sky. And as I like to say, that’s where all the good stuff always is. I tried to estimate the visual limiting magnitude; it seems like it’s about 4.0, a drop darker than my 3.8 skies back in Glendale.
The scope cooled down for a good 40 minutes while I brought everything out from the house to the car, and then from the car to my observing spot and got set up. I first had to figure out where to attach the 6×30 crosshair finder. There were three pairs of screws along the back edge of the C9.25 where it could go.
But first I had to figure out whether the scope was upside down or not. I tried some fake alignments to see how the scope would automatically slew from the first alignment star to the second one. Yup, the scope was upside down. But fortunately, not in the upside down, because that would have been a major hassle. I learned that with the Sirius Pro mount, when the scope is horizontal, you have to have the mount screws on top, or else the scope is 180 degrees off.
I hadn’t used an optical finder since I was a kid with my equatorially mounted newts. I screwed it in place, and then aligned it with a far off blinking red light on a radio tower. The 6×30 served its purpose well, helping me center my alignment stars. I don’t see any need for replacing it with an RDF.
I checked the collimation by defocusing on Capella and got a perfect donut shape. Phew! That’s a relief. Yeah, there was some wiggling and wobbling in the bright part of the donut because the scope hadn’t fully cooled down yet, but the shape was correct.
I then started with some old friends I hadn’t seen since last year – the winter open clusters, M35 through 38. They were gorgeous – much more full, filled in, than through the Mak. The extra 1.5 magnitudes from the extra 4 1/2 inches of aperture really makes a big difference, which was the entire idea behind getting this scope. M35 was particularly nice, beautifully filling the entire 0.69 degree field of view of the ES 24mm with sparkling little diamonds.
Focus was sharp – the stars were pinpoints from edge to edge. It was also relatively easy to achieve a good focus. In the Mak, there is some lag between when you turn the focus knob one way and then the other – the change in focus when reversing directions is not instantaneous. It’s like the focusing gears have some play in them, some backlash. There seems to be significantly less of this in the SCT, making it much easier to achieve a precise focus.
After these warmup open clusters, I turned to the piece de resistance, the non plus ultra, the creme de la creme (yes, I took French), my very favorite DSO, come on, say it with me now: the Great Orion Nebula.
And it was glorious. I observed it for 20 minutes straight, it was so glorious. Previously, observing with the Mak, I’ve seen some texture, some structure. But this? This was ridiculous. The mottling in the clouds was very clear. For the first time, it was very, very apparent to me that the whole nebula was being lit up just by the Trapezium, as opposed to the line of three stars having anything to do with it.
The dim star (the B star) of the Trapezium was a beautiful orange – which I had seen before in the Mak, and smaller apertures. I switched back and forth between using the Orion Ultrablock filter and not. The overall image dims with it – the B star was still visible, but close to winking out. The Ultrablock is designed to block light pollution, while also increasing contrast. The structure of the nebula just pops right out at you. It looks 3-D.
It looked not unlike the image at thet top of this post. Well, except that that image has color and goes about two magnitudes deeper than what I could see. I’m talking about the structure in the photo – most of it was present visually. The fish’s mouth was easy to see; it’s one of the easier features to see in any scope. I could also see a dark patch that the three stars were pointing to. The “bat wings” extended out from either side. M43 was definitely more apparent, although there was no “Running Man” to be seen there.
The ES 24mm gives me almost 100x, which is a nice magnification for DSOs. I almost forgot that with this lovely extra aperture, I might be able to catch the E and F stars of the Trapezium for the first time. Both are 11th magnitude. And I did!
I slipped in my 60-degree AstroTech Paradigm 15mm (same as the Agena StarGuider) to get me just past 150x, and then my 12.5mm KK Fujiyama ortho to go to almost 200x. The seeing was good – the image held steady. And there it was, the E star, barely visible between A and B, but definitely there. I was using averted vision on the Trap, wearing my eyepatch, and covering my eyes from ambient light, trying to squeeze out that extra little bit of light. (I forgot to bring a dark t-shirt to use as a hood.) As I did so, I was catching a slightly dimmer star from time to time off behind the C star. The F star! Mission accomplished!
I continued observing. M78 was nearby. It was trivial to find, a little patch of haze that was definitely right there. In the Mak, I had to tap the scope, move the field of view, and use averted vision to make sure I was seeing it. M81 and 82 were around, but they were disappointing. I had seen some structure in one or the other (I always forget which is which) out at a dark site. While they were clearly visible and M82’s cigar shape was apparent, I couldn’t make out much more than that. Oh well, I guess I’ll just have to bring the scope out to the club’s dark site and give it another go!
I tried for Andromeda, but I had done my alignment on Castor and Rigel. Andromeda was way off in the other direction, so the alignment was just too far off to even find it. Yup, the entire galaxy was missing. I also had totally forgotten that Castor was a double – actually a double-double-double! With the ES 24mm at 98x, I could just split them cleanly – two bright white stars nestled up nice and close to each other.
After a realignment, the scope put me on what I thought was M31, but it turned out to be M32. Yup, the satellite galaxy was so bright, I mistook it for the real thing. Moving to M31’s core, it was very bright. But it was relatively disappointing, as always. No structure, no resolution. Just a bright core surrounded by gray.
The Pleiades were practically directly overhead, but through a tight 0.69 degree field of view, it was difficult to even figure out which part of them I was looking at. On the other hand, they were gorgeously bright, bluish white jewels. I tried for the Double Cluster, but the slewing was off again, and by this time, my patience was thin, as was a high haze which had come in from the west. And after being out for almost two hours, I was starting to get cold.
Before packing it in, I went back to the eastern sky, where it was still clear, and took a look at some other old winter favorites, some star clusters down Sirius’ way: M41, M47, and M48. Even though they were only about 15 degrees above the horizon, they all still looked very nice, very full.
All in all, I am very happy with the scope so far. The views are nice, so much brighter than my Mak. And the focus is wonderfully sharp – far sharper than I expected an SCT to be able to deliver. Many people say that the optics in the C9.25 hit the sweet spot somehow. I don’t doubt it. I will have to take it out to the dark site and test it out on galaxies at some point.
The mount, well, not so much. I’ll have to work on it some. Hopefully, next time I use it, I’ll put the Mak and ‘frac on the other side; maybe the weight will balance it out and make it perform better? I’m also going to look into controlling it from my laptop instead of the handset. The software in the handset is just so clunky compared to the NexStar. The NexStar works logically; or, in other words, the logic of how it works makes sense to me. The Sirius, not so much. Maybe it’ll become clearer to me with more use.
Banner photo: Credit J. Lodigrus
Light-Polluted Astronomy 
Nice one Jon.
On Mon, Jan 8, 2018 at 9:09 PM Light-Polluted Astronomy wrote:
> Jon posted: “Well, I’ve finally done it! I’ve finally bought my long > sought after Celestron 9.25-inch optical tube assembly (OTA). I had been > very patient, waiting and waiting for a used one to come up for sale at a > reasonable price with the newer Starbright XLT coa” >
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Great article, enjoyed the read.
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