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Celestron 9.25: A Good Scope But No Real Mystery


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The Decision

I admit it. One of the reasons I first looked at this odd-sized Schmidt-Cassegrain was that, like so many others, I had heard the internet born rumors surrounding the Celestron 9.25. Although no one could explain exactly why, this SCT was thought to be different. One of the early reviewers called it the SCT for people who hated SCTs. Some said it was created as an optical experiment by one of the company's former owners. Others raved about the contrast. They likened the scope to an apo-- the greatest thing since Newton first used a mirror to gather light, they said. It was supposed to have a cult following, which always sounds intriguing. Celestron wasn't confirming any of the stories, but they did little to dispel the notions. It was free advertising, after all. And, as it turned out, there really was a kernel of truth behind the rumors-- a small kernel, but undeniably present. At any rate, I was interested.

So I did my homework. This was to be my first telescope, or at least my first since a dimly recalled early sixties refractor of what must have been 60mm. Money was tight and I had to make the right decision. I knew this wouldn't be a passing fancy, and wanted to push the inevitable aperture upgrade into the distant future. In this, of course, I ultimately failed, but I did give it a try.

I needed a fairly big scope that was still manageable. I had read the maxim equating "best" with "most used." It also had to be good for planetary observation. And, knowing myself and having an inkling of the problems inherent to light pollution, I wanted the go-to technology. Additionally I wanted an equatorial mount, which in the future wouldn't limit me to just one OTA. Finally, I suspected that I would eventually try my hand at astrophotography. Lacking the funds necessary for long exposure work, I would probably begin that journey within the confines of our solar system, which would be easier with a slower focal ratio. So, in other words, I needed a light gathering, high-tech, planet killing, high magnification, inexpensive, observational astrograph that I could easily transport.

Of course I soon found out that no telescope excels at every task. There are always quality and feature tradeoffs involved in any scope decision, and most people who stick with the hobby for any length of time end up with more than one telescope. That wasn't exactly what I wanted to hear. What I needed was a jack of all trades and master of none-- which, in the end, brings us to the Schmidt-Cassegrain telescope. Now it was just a matter of size.

Celestron Advanced Series


After six months of research I decided on the C9.25 with Celestron's Advanced Series. This would give me the equatorial mount, a CG5 Vixen clone with go-to, at a manageable combined weight of 69 pounds. I would have plenty of aperture without being as seeing dependant as some of the larger models. I ordered mine from Astronomics, which still lists the AS9.25 for $1,779.00 .

Having read about the quality and size of the finder scopes often supplied by both Celestron and Meade, I ordered an 8x50 Anteres RACI along with the telescope. At the same time I ordered a set of Bob's Knobs, which are thumbscrews that replace the collimation screws on the secondary housing. Finally I ordered a William Optics 2” diagonal to replace the 1.25” diagonal that Celestron supplies.

Regarding the rumors, the truth about this telescope turned out to be pretty simple and not at all mysterious. In the days before CCD chips took over astrophotography and film was still king, Celestron simply tried their hand at making an SCT that was somewhat better suited for film photographers. Celestron and Meade had always used spherical primary mirrors with an f/2 focal ratio and a secondary with a negative focal ratio of f/5 giving the optical system an overall ratio of f/10.

This time Celestron tried something a little different. They made an f/2.3 primary, which would put less strain on the secondary, this time figured at f/4.3, creating wider collimation tolerances and, most importantly, producing a flatter field with less coma. This also resulted in a slight physical difference. A C9.25 has a proportionately longer optical tube than other SCTs. It is, for example, nearly the length of the C11. Whether or not these focal length differences are visible at the eyepiece is a matter for debate. If there really is a difference, then it is slight. I'm unable to see it, and can't honestly report that it is visually superior to other Schmidt-Cassegrains. All I know for a certainty is that the C9.25 is an excellent telescope. It has great optics and, for my needs, it is as close to a perfect size as is possible. It has enough aperture to pull in the DSOs without being difficult to handle. The OTA only weighs 21 pounds.


First Light and the First Year

By the time UPS dropped off three large packages on my doorstep, I had already downloaded and read the manual three or four times. To say that I'm not mechanically inclined is an understatement, but the setup process was a lot easier than I anticipated. It took no more than forty-five minutes. All of the components were well packed and survived the trip with no damage.

I had ordered a set of JMI’s Wheely Bars to make the scope, mount and tripod more portable around the house, but didn’t have them yet. Nevertheless, the entire setup only weighed 69 pounds and wasn’t difficult to carry into the back yard. I didn't attempt to use the go-to for the first few nights, but when I did, it worked exactly as advertised. The manual is well written and the alignment procedures are straight forward. I always use a procedural option which allows the selection of alignment stars of your choice. I usually stick with two sets of star choices for a month or two, changing once the star locations have “moved” across the sky significantly. I say two sets, because as the night progresses your go-to accuracy will gradually degrade. After a few hours it may become necessary to re-align using a different set of stars.

I've been very pleased with the accuracy of this system. It almost never fails to place the target somewhere within the field of view. The alignment procedure can be a little tricky at first, and might have given me problems had I not read about it in the forums. It is important when slewing toward your chosen star to end the slew with the “up” and “right” arrows. Sometimes means having to first purposely overshoot the mark. I had heard stories of runaway slews, but it's only happened to me two or three times. The cooling process hasn't been a problem either. On week days I put the scope outside as soon as I get home from work. By the time dinner is finished, the scope has nearly always reached thermal equilibrium. I recall only two occasions in the first year when more time was needed.

Much has been written about image shift and SCTs. In one of the other SCTs I have tried I did notice slight problems, but that hasn't been the case with my C9.25. Focusing is easy and the 2” steel tripod legs are sturdy enough to support the weight of the OTA without a lot of vibration. When I began to use this scope for webcam imaging, focus became more of an issue and I decided to go with a third party dual-speed focuser. Again, my C9.25's focus system was quite adequate for most purposes, but I needed the fine focus. Another thing to consider is that a Crayford type focuser can eliminate or at least prolong eventual SCT mirror flop by eliminating the need to constantly move the primary mirror back and forth.



From the first night on, I have always used a rough polar alignment, simply putting Polaris near the center of the polar scope hole. Actually, for visual use, this is not strictly necessary. There have been times when I've just set up in an area of the yard where Polaris is hidden by trees. Whenever this happens I just point the mount north, and it still tracks reasonably well. A rough polar alignment, of course, is a better way to go. It will enable you to walk away from the scope and return 45 minutes later to find your target still at the edge of the FOV.

Since my first light experience was also my first experience, I had no basis for comparison and everything looked great. Not many SCT first light reports spend much time on views of the stars, which are really the forte of refractors and other optical designs, but I had never looked through an apo or a Maksutov-Newtonian and didn’t know if I was missing anything. It was early winter and I was astounded by the views of M37 and the other open clusters. Later I would understand that this scope doesn't quite produce the contrast or the pinpoint stars you would get with those other scopes, but the optics are not bad at all. On the contrary, they are excellent. It's true that you still won't get as wide a field of view as with the “slower” telescopes, but to see the Double Cluster through a C9.25 with a good 2” diagonal and a 30mm eyepiece is still an awe inspiring experience. The first time I looked at the Double Cluster using the C9.25 and an eyepiece that gave me a true field of view of 54 arc minutes, I immediately understood what the eyepiece reviewers meant by taking a walk in space. I would suggest to any new SCT owner that they replace the 1.25” diagonal as soon as possible. Until they do, they're really not getting the full extent of their scope's capabilities. Also, with an SCT, you can get those panoramic views without breaking the bank. One of the advantages of an f/10 SCT is that you can take advantage of some of the less expensive but decent 2” eyepieces coming out of Taiwan and China. With slower scopes there won't be nearly as much edge-of-field distortion as with a faster reflector or refractor.

I soon got over my initial fear of the collimation process. On the first day I decided to install Bob's Knobs, but the installation knocked the scope's optics so far out of alignment that I was forced to learn collimation then and there. It turned out to be simpler than I had suspected. Now, during nearly every session, as soon as seeing becomes stable enough, I put in a high powered eyepiece and star check the collimation, making adjustments when necessary.

There are general rules of thumb regarding magnification, but it's really a subjective issue. Image softness that I might find intolerable may be okay for someone else. And everyone's eyes are different. At any rate, for planetary observation with the C9.25, my experience has been that 133x to 150x are near optimum magnification levels on nights of average to good seeing conditions. I have, on rare occasions, been able to increase magnification to 250 comfortably, and even more for lunar observation.

Images of Saturn at magnification levels of 100x to 150x were stunning. At 133x, on nights of excellent seeing, the Cassini division showed up as a sharp, jet black line separating the A and B rings all the way around. Even on nights of mediocre seeing the planet's sphere showed color. On better nights a band and the polar cap stood out.

Jupiter was just as good, but I didn't fully appreciate it until the second year I had the scope. My expectations may have been a little high, and as any experienced observer knows, it takes time to learn how to see. But whenever it faces us the GRS is always apparent with this scope, even on nights of average seeing. I don't believe I've ever failed to see it. What impressed me the most was that, under the best seeing conditions, the larger of the Galilean moons were resolved as tiny spheres rather than points of light. They looked like moons.

I live in a light polluted suburb, where, on the darkest nights of the year, the upper levels of my eastern sky will show stars of 5.0. Normally dark nights will be populated by stars in the 4 to 4.5 range, usually closer to 4. Fortunately we have better than average seeing. During my first year with the C9.25 I saw the entire Messier catalogue from this location. A few of these were difficult, such as M74 and M101, the latter of which took more than a month of searching every night, until we finally had a night dark enough to differentiate between the pale light of the galaxy and the background sky. In M42's Trapezium I can see A through E on a good night. On a very good night I can see all six, the F star popping in and out of view. With the go-to function, this scope showed me 132 galaxies during that first year. I didn't get much sleep.

And finally we come to the reason that Celestron made this scope differently than all other commercial SCTs—a flat field for astrophotographers. In the end it didn't matter. Within a few short years film faded into astrophotography history. CCD fields grew wider, but with so many reasonably priced telescopes and accessories (such as ED refractors and field flatteners) hitting the market with each month that passed, there was less of a need for such an OTA. Ironically, when this scope became one of the OTAs of choice for planetary and lunar photographers, the flat field didn't even matter. These targets were always within the mirror's “sweet spot” anyway. It was the focal length and aperture that attracted the planetary imagers to the SCTs.

There has been some talk on the internet to the effect that this C9.25 is better than other SCTs for planetary or high magnification lunar imaging. If there is any truth to this, then it doesn't have anything to do with the optics. If there is indeed a disproportionately high number of quality images surfacing that were captured with this telescope, then it is probably due to the fact that this OTA is less dependent on seeing conditions and doesn't take as long to cool as the larger SCTs. Under the right circumstances a properly cooled and collimated C14 will, of course, resolve more detail than the smaller scope. With the smaller OTA you just get more chances. So, once again, this isn't a magical scope, but for planetary imaging there are distinct advantages: with 9.25 inches of aperture it will resolve a lot of detail and you will have plenty of opportunities to capture it. Here is an image I took toward the end of the first year with this scope:


Conclusions

In summation this is an excellent telescope, and I say this with even more conviction now than when I first acquired it. I now have a 12” reflector that shows me a little more, but overall I prefer the SCT. It is a much more comfortable scope to use and does a little of everything. I don’t really consider the reflector portable, while the C9.25 is easy to break down and throw in the trunk of a small car. If I could have only one telescope, it would have to be this.

To call any SCT a jack of all trades is accurate, but to end that thought by saying that it is a master of none does not tell the whole story. For one thing, they really are masters of planetary imaging. There are other areas too, such as DSO observing, where, inch for inch, an SCT is very close to some of its rivals. Still other areas, such as wide field observing or focusing, which are commonly considered an SCTs weak points, are to a large degree corrected by the addition of third party fixes. A good 2” inch diagonal and a Feathertouch focuser make the C9.25 a true pleasure to use. In short, I don't see how anyone could be displeased with this telescope, even first-time scope buyers like myself. You may eventually want to add a refractor to the lineup, but I'll bet you keep the C9.25.

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