I have pretty much made up my mind as to what I’m going to do in terms of my jump up in aperture. Well, to be more grammatically correct, I had pretty much made up my mind. As I discussed in this blog post a couple of months ago, I was basically looking at using my Jeopardy “winnings” (remember, 2nd place gets $2000, and 3rd gets $1000, so those are still winnings!) and the savings in my “telescope account” to buy the Skywatcher AZ-EQ5 mount and put a used Celestron 9.25-inch SCT on it. (Watch me on Jeopardy on May 25th!) Since the entire point of my getting a larger scope was, well, to get the larger scope possible, this made the most sense to me. More aperture = more light grasp, and the C9.25 gets me one and a half magnitudes deeper than my 5-inch Mak. That’s pretty darned significant.
Christopher Sullivan, a guy I “know” from around the Facebook astronomy boards, and who has graciously allowed me to post a few of his astrophotos here in the blog, told me a couple of weeks ago that Orion is running a sale on its Sirius Pro AZ/EQ-G mount. This is the exact same mount as the Skywatcher, except Orion’s is in black, while the Skywatcher is white. Moreover, the sale was a BIG ONE: $280 off the regular price, only $1119. Gulp! That’s one heckuva savings!
It seems that the sale runs through to the end of the month – but don’t quote me on that; I’m not exactly sure of my sources for that info. But it has been two weeks since I learned of the sale, and it’s still on. Out of an excess of financial conservatism, I had been waiting for the sale of my apartment back in New York before pulling the trigger on this upgrade. But this is just too good of a deal, too much of a savings, for my genetically frugal nature to pass up. After reading up on the mount, procrastinating, and some dilly-dallying, I finally clicked the buy button today; I should have the mount by next week. Yay!
In doing my research on the mount these past couple of weeks, I did learn of a known problem that the Sirius Pro/AZ-EQ5 (and the SW AZ-EQ5 as well) suffered from – excessive wobble, mechanical play in the declination axis, especially when used in Alt-Az mode. People reporting this describe it as being unacceptable in terms of how much the image moves around in the view, either while focusing or due to even light winds.
However, the mount has been out for over two years now, and hopefully this “known” problem has been dealt with by now. Further, one of the things that Orion is known for is their customer service. When I asked Orion customer support about this problem straight out, they told me that this seemed to be an isolated issue, and of course, they would work with me to correct it if it cropped up on my mount.
Now, there’s no rush for me to go buy that larger scope that I really, really want to put on this mount. Just like I waited a few months on the mount, I can wait some for the new scope, too. I am and have always been a patient guy in the material acquisitions department. But what’s the point in spending $1119 on a mount if it’s not going to let me see more, right? Because at this point, all I’m going to do is put my same little ol’ 5-inch Mak on it, with the ST-80 refractor strapped on.
I’ve been looking around at used C.9.25s to buy for quite a while now: I’ve been subscribed to the Cloudy Nights’ “Cats and Casses” classifieds for months. In case you don’t know, you can go to the Cloudy Nights classifieds section, pick out what broad categories of scopes/equipment you’re interested in, and they’ll send you an email anytime anyone lists something for sale, or updates that listing. I enjoy it if only to keep my finger on the pulse of what used stuff costs. Used C9.25s are generally listed in the $650-800 range – some a little less, some a little more, depending on what accessories come with them.
CN lets you do a search of the ads to find exactly the model what you’re looking for. Of course, being the ubernerd that I am, I prepared a spreadsheet of all the C9.25s listed. 20 of them came up for sale in 2015; 18 in 2016. But only 4 so far this year. That’s way behind pace, people! You gotta put those C9.25s up for sale already!
CN’s classified email service isn’t discriminatory – if you sign up for “Cats and Casses”, you get all of the Cats and Casses, not just the models you might be interested in. Having decided to buy the Sirius Pro, what comes along but an ad for a 10-inch Meade SCT. And for cheap, to boot.
Now, I don’t know nothin’ ’bout no Meades – except for the fact that my piece of sh–, um, I mean junk, Bird-Jones scope that I bought about a dozen years ago was a Meade. On the other hand, the 8-inch newt I had as a kid 35 years ago was also a Meade. But I’ve heard that with all the changes in Meade’s ownership over the past 20 years or so, Meade’s quality has been slipping of late, especially during the 00s. Between this and my Bird-Jones experience, I’ve been steadfastly ignoring them since my long-awaited return to astronomy 3 years ago.
Just like the split between PCs and Macs (not Maks, heh heh), I come down squarely on the Celestron side. Just like PCs, I am very well familiar with the Celestron universe of scopes, mounts, how they interact, what all the different letters mean. But Meades? Fuhgeddaboudit. No clue.
Well, until I saw that CN ad for one, that is. The 10-inch Meade was a good $100 less than the least expensive 9.25-inch Celestrons I had been seeing. Hmmm. My cheapitude springs into action once again! Off I went to research the heretofore unknown to me Meade universe.
Celestron SCTs had a dual-track in terms of their optics. There are some SCTs with “Starbright” coatings, and then there are some with “Starbright XLT” coatings. Optical surfaces need to be coated to keep them from reflecting or scattering light in ways that aren’t helpful. This is why you can see your reflection in, say, the clear glass in your window, but hopefully not so much in your SCT corrector plate.
The non-XLT Starbright coatings indicate an older type of coating, on an older SCT. In an SCT with non-XLT Starbright coatings, they transmitted about 72% of the light reaching them, depending on the wavelength. Remember that an SCT has three optical surfaces – the corrector plate, the primary, and the secondary. Each surface absorbs or otherwise scatters some light. For example, if each of the three optical surfaces transmits 90% of the light, then 0.9×0.9×0.9 = 73%.
The Starbright XLT coatings are newer; and are also just that much better. They transmit about 83% of the light reaching them. More to my point, in looking for a C9.25, I’m looking for one with the XLT coatings. There are two reasons. One is that XLT coatings mean that I’m dealing with a much newer scope. Celestron pretty much discontinued the “non-XLT Starbright” coatings once they introduced the “Starbright XLT” coatings around 2003, so those older scopes are about 15 years old. In this vein, coatings do “evaporate” or otherwise “go away” over time. Not instantly, not to a huge degree, but they do, and less coatings means less transmitted light.
The second reason is that the entire reason I’m doing this is to get more light. Even though an 11% increase is just on this side of perceptibility to the human eye, yeah, I want the better, newer coatings. And who doesn’t want a newer scope anyway? A newer scope means it’s had that much less time to be banged around, that much less time for things to go wrong with it.
The Meade universe of SCTs is more problematic – for me, at least – because the OTAs are permanently attached to the fork tubes of the mount they’re on. They have to be “deforked” to be used on any other mount, and by someone who knows what they’re doing. Then, to attach a deforked Meade OTA to another mount, you need to permanently attach a rail, whether of the Vixen or Losmandy type, to the bottom of the OTA. So, not exactly ideal for my situation, a mechanical klutz with no garage or tools to do this anyway.
Just like the Celestrons, the Meades, too, had a dual-track coating system. Originally the coating system was called EMC. But around the same time as the Celestron’s XLT coating came into existence, Meade introduced their UHTC = “Ultra-High Transmission Coating”. In fact, it was the other way around – Meade’s introduction of the UHTC led to Celestron’s introduction of the XLT shortly thereafter. And the performance improvement in terms of light transmission from Meade’s EMC to the UHTC was similar to that between the non-XLT to the XLT.
So again, even in the Meade universe, I would want a UHTC scope rather than an EMC one for the same reasons. I’m just not that interested in a 15-year-old – or older! – scope. The problem is that many of the UHTC Meades were made in the 00s – right around the time of the quality-control problems Meade was experiencing. I bought my dreaded Bird-Jones from Meade at that time as well. Not only was the telescope itself a piece of junk optically, but the mount also developed a “motor fault” after about a dozen uses and became useless from that point on. Not good.
Notably, it looks like Meade has gone fully high-end with all of their SCTs. For example, Celestron sells “regular” SCTs, and they also sell the Edge HD version. This leads me to discuss my pet peeve about SCTs in the first place – the corrector plate. In a regular SCT, the corrector plate is supposed to correct for the fact that SCTs use a spherical mirror. But it doesn’t. There are still some aberrations left, including coma and field curvature. Obviously, the corrector plate doesn’t do that great of a job of correcting.
Enter the Celestron Edge HD line of SCTs. These have two lenses in the baffle tube down by the focuser to correct for what the corrector plate doesn’t correct. Which means that the corrector plate is definitely lying down on the job. I think it should be called the “semi-corrector plate.”
Meade’s equivalent to the Edge HD – which is now their only line of SCTs – is called the “Advanced Coma Free”, or ACF. Instead of adding additional glass in the optical path, Meade has “corrected” the “corrector plate” in what I, expert optician that I am, consider to be the, ahem, “correct” way – they’ve refigured the corrector plate so that it alone eliminates the aberrations. Interestingly, even with what seems to this untrained eye to be a superior correcting system, most of the top planetary astrophotographers – who need as large of an aperture as possible, because greater aperture means greater detail – use the Celestron Edge HD, and not the Meade ACF.
Now, you would think that the extra three-quarters of an inch of aperture in a Meade 10-inch over a Celestron 9.25-inch scope would add some significant amount of light gathering. Unfortunately, it doesn’t. It’s just an extra quarter of a magnitude, and that’s barely perceptible. On the other hand, that’s about the same improvement you get from these newer coatings, so why not, right? And saving $100 or more on an even larger scope is always nice.
However, Meade is known for having their scopes be more beefy than other brands. So the Meade 10″ optical tube weighs about 28 lbs. versus the about 20 lbs. of the C9.25. And that 28 lbs. is without the mounting rail or finder on the Meade. The SW AZ-EQ5 – oops! I mean the Sirius Pro – is supposed to be able to handle that weight, as it’s rated to 33 lbs. per side. But 28 lbs. plus could be pushing the capabilities of the mount just for the sake of just an extra quarter magnitude. Maybe it’s better not to experiment that way.
The very helpful wags over at Cloudy Nights are telling me that there is no optical difference, or if there is, it is incredibly slight – and possibly in favor of the C9.25, which has better contrast. This is because the focal ratio of the primary mirror in the C9.25 is slightly slower than all other SCTs – and slower is always better in terms of aberrations. The C9.25 it is, then – unless some amazing 10″ Meade practically falls into my lap for cheap. Now I just have to wait for a good one to come up for sale.