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What aperture costs

August 14, 2012

Just for the heck of it, I decided to find out which telescopes are the best deals in terms of light grasp. My comparison group consists of widely available commercial dobsonian reflectors ranging from 3″ to 16″ in aperture. Sometimes I included two models at the same aperture to show the effect of differing features, like the finder scope and better eyepieces on the Orion Funscope versus the Celestron Firstscope, or the collapsing truss-tube design on the Meade Lightbridge scopes. Prices are street, not list, as of this writing. Each entry follows this layout:

Brand Model – mirror diameter (mm) – mirror area (in^2) – price – cost per in^2

Celestron Firstscope – 76mm – 7.065 in^2 – $38 – $5.38/in^2

Orion Funscope – 76mm – 7.065 in^2 – $50 – $7.08/in^2

Orion SkyScanner – 100mm – 12.56 in^2 – $100 – $7.96/in^2

Orion StarBlast 4.5 – 114mm – 15.89 in^2 – $200 – $12.59/in^2

Bushnell Ares 5 – 127mm – 19.63 in^2 – $165 – $8.41/in^2

Orion StarBlast 6 – 150mm – 28.26 in^2 – $280 – $9.91/in^2

Orion XT6 – 150mm – 28.26 in^2 – $280 – $9.91/in^2

Orion XT8 – 200mm – 50.24 in^2 – $350 – $6.97/in^2

Orion XT10 – 250mm – 78.5 in^2 – $580 – $7.39/in^2

Meade 10″ Lightbridge – 250mm – 78.5 in^2 – $700 – $8.92/in^2

Meade 12″ Lightbridge – 300mm – 113 in^2 – $1000 – $8.85/in^2

Orion XT12i – 300mm – 113 in^2 – $1100 – $9.73/in^2

Orion XX14i – 350mm – 154 in^2 – $1700 – $11.04/in^2

Meade 16″ Lightbridge – 400mm – 200 in^2 – $2000 – $10.00/in^2

Interestingly, there are two low points where the price dips below eight bucks per square inch: at the low end, with the 3″ scopes, and in the middle, with the 8″ and 10″ solid-tube dobs. It’s also interesting to note that the StarBlast 4.5, which is an extremely popular scope, is the most expensive in this group in terms of cost per square inch.

I only included dobs because everything else is more expensive–tripod-mounted Newtonians, catadioptrics, and refractors alike. Here are some comparative costs for beginner instruments of those other designs; for fairness, I only picked models with mounts included.

Orion SpaceProbe 3 Alt-Az (reflector) – 76mm – 7.065 in^2 – $100 – $14.15/in^2

Orion GoScope 80 (refractor) – 80mm – 7.74 in^2 – $100 – $12.92/in^2

Orion StarMax 90 Tabletop (catadioptric) – 90mm – 9.85 in^2 – $200 – $20.30/in^2

The difference here is that there is no mid-aperture dip as there is for the dobs, or if there is, it doesn’t bring the price per square inch near the $10 mark, let alone under it. Indeed, one would be hard-pressed to find a new, high quality 4″ achromatic refractor for less than $300-400, which is up in the neighborhood of $30/in^2. Similar prices obtain for mounted 5″ Maks and 8″ SCTs. That’s why I didn’t bother to account for the effect of the central obstructions in calculating the costs of the reflectors and catadioptrics; even what seem to be large secondary obstructions are usually less than 10% of the total collecting area, and dobs cost anywhere from a half to a fifth as much as other popular, “everyman’s” scopes in terms of collecting area.

Now,  I’m not saying that dobs are objectively superior to other scope designs. They’re cheaper. We all knew that, I’ve just quantified it, snapshot style, using currently available models and prices. I did it because I had a gut feeling that 8″ and 10″ solid-tube dobs were in sort of a sweet spot, price-wise, and that actual costs (per square inch of collecting area) rose a bit on either side. And they do.

Finally, these numbers put some classic deals into perspective. When the SkyWatcher 130N was on sale for $100, its cost was just a hair over five bucks per square inch–better than any of the models listed above by a considerable margin. The SkyWatcher 70AR was at one point selling for $36 shipped, or just a hair rover six bucks–a bit more expensive, per square inch, than the Celestron Firstscope, but for a much more capable instrument. I think the  only refractor deal in history that has ever equalled that was the Galileoscope. With 50mm of aperture and an introductory price of $15, it was originally selling for $4.78/in^2, but that was without a mount. Similarly, the value of buying used is now apparent–when I got my XT10 for $350, that was a cost per square inch of $4.46, much less than any of the new scopes, even the cheapies.

What should you buy? That’s a more complicated question, and it can only be answered by reference to your situation and your observing goals. I own a mid-sized Mak because sometimes it’s nice to have 5″ of light grasp in a package a foot long, and I bought it new because sometimes it’s nice to have something fresh off the line. But if you’re interested in deep-sky work, where every photon counts, and you’re on a budget, then you might find the numbers above useful in considering which scope will give you the most bang for your buck, or for evaluating future scopes.

Why you want as much aperture as you can get is the subject of the next post–and for a contrary view, see this post.

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9 comments

  1. Matt,

    REALLY interesting stuff. The 8″ to 10″ definitely delivers the biggest bang for the buck, but then you have the size and (lack of) portability issue to deal with, though I understand that this is not part of the equation in your study/analysis. But huge light-gathering at relative bargain prices (and with manageable size) is obviously to be best had in this 8-10 sweet spot.

    What really jumped out at me was the WAY high cost per aperture inch of the StarBlast 4.5, maybe THE most popular entry-level scope out there right now. But hardly a bargain in terms of pure light-gathering. Obviously the relatively low cost (under $200), true portability, and ease of use all factor in here in accounting for its popularity. But the StarBlast 6 is a significantly greater bargain from a performance standpoint; however, as a SB 6 owner, its not really a grab and go, more as another SB 6 owner up here defines it: “a mobile rig”. But for light-gathering alone, the extra money would be more than well spent vis a viz the 4.5

    So I wonder: How many SB 4.5 buyers over the past few years would have moved up to the 6 had they seen your chart beforehand? Because for pure proton plucking, the 4.5 is unquestionably overpriced, and the 6 much more the bargain.

    Another no-brainer would be that the SkyScanner 100 is close to the same cost per aperture inch as the FunScope but delivers way more performance. Based on Terry’s many posts on the SS 100, we know what a fine instrument it is, along with being a true one-hand grab-and-go (and over $4.50 per inch less than the 4.5).

    Seems hard to figure how anyone who sees your chart would opt for the FunScope over the SkyScanner, as size and portability is a non-issue.

    I picked up a SS 100 a couple of weeks ago, and Terry is spot-on: It’s just a superb scope, and (for $100 scope) about as portable as a serious instrument can get. I just move it all over the place, table to table, with almost bino-ease.

    Nice to see how well the SS 100 holds up as a true bargain, as per your cost analysis. Give some thought to getting one yourself for your Urban Messier Project.

    Nicely done, Matt. Very entertaining and, for those just coming on board at 10MA and contemplating a new scope purchase, most valuable.


  2. What really jumped out at me was the WAY high cost per aperture inch of the StarBlast 4.5, maybe THE most popular entry-level scope out there right now. […] So I wonder: How many SB 4.5 buyers over the past few years would have moved up to the 6 had they seen your chart beforehand? Because for pure proton plucking, the 4.5 is unquestionably overpriced, and the 6 much more the bargain.

    Well. I think that the StarBlast 4.5 was really the first non-junky, fully capable scope to retail for under $300 (except the Astroscan, I guess, but that’s such a weird duck that it sort of stands alone). My perception is that its price has stayed pretty much the same for the past decade, and new affordable scopes have been introduced on either side that compete with it–namely the StarBlast 6 on the bigger/slightly more expensive side, and the SkyScanner 100 on the cheaper/slightly smaller side.

    And, as you point out, it offers certain advantages over both of its close competitors: it’s considerably more portable than the 6, and optically and mechanically a little nicer than the SkyScanner. It’s a lot of attention to lavish on a 4.5″ scope, which I think accounts for its relatively high cost per square inch. The StarBlast 6 has all the same bling, basically the extra dough covers the bigger mirror and a little more steel tube and particle board, none of which make it that much more expensive.

    Seems hard to figure how anyone who sees your chart would opt for the FunScope over the SkyScanner, as size and portability is a non-issue.

    Two things come to mind. One is that I think a lot of people are buying FunScopes for their kids, and for a kid, the difference in size between a FunScope and a SkyScanner might be a bigger deal (plus, the FunScope is cute!).

    The other is that some people might not have $100 to spend on a telescope; it might be the FirstScope, the FunScope, binoculars, or nothing. Certainly the FirstScope and FunScope have their limitations, but given that each one costs about as much as a new Plossl, they’re pretty amazing achievements, and I’m glad they’re available. Although at that price point my preference would be for Celestron’s 10×50 or 15×70 binoculars.

    Nice to see how well the SS 100 holds up as a true bargain, as per your cost analysis. Give some thought to getting one yourself for your Urban Messier Project.

    I have been thinking about one, very seriously. But that will be a subject for another post. Thanks for your kind words on this one. Running the numbers was an eye-opener for me, too.


  3. […] Astronomy Stargazing for people who think they don't have time for stargazing. « What aperture costs Why aperture matters August 15, […]


  4. Matt,

    Agree on the binoculars as a better choice for a (non-kid) entry into astronomy over the FirstScope or FunScope. I have a pair of Celestron 15 x 70 SkyMasters, the first instrument I bought, this back in January when I decided to get into astronomy, something I had thought about for decades but done little about. I think I paid about $62, shipped, from Amazon, so just a bit more than the FunScope. I still use them all the time and am amazed at how much I can see and how BRIGHT images are, much brighter than what I see in my FirstScope which has 6mm more aperture. I guess this is attributed to both superior optics in the SkyMasters and that you are using both eyes. Whatever, they really open up the heavens. I also have a pair of Orion Scenix 10 x 50s that I picked up brand new on eBay for $40 and while they have superb fit and finish and an incredible 7-degree FOV, the images just don’t have anywhere near the “pop” that they do in the SkyMasters which I probably use about 75% of the time. If someone didn’t have $100 to spend and was leaning toward the FirstScope, I would instantly recommend that they instead opt for the 15 x 70s. Sometimes I go out for an hour with them and just lie back and look around.

    But the little SkyScanner does up the ante, and noticeably, even over the 15 x 70s. At 40x and 67x (with 10mm and Expanse 6mm EPs), I can capture a lot more distant stuff than I can with the SkyMasters and with the same level of brightness. And the little sucker weighs barely more than the binocs. It is just such a totally manageable little telescope, and also scores high on the cute scale

    You are right about the StarBlast 4.5 and why it has such appeal. I think Orion put a lot of r & d into it, and it shows. Everything about it, and the SB 6, just plain works. And the 4.5 is really significantly smaller and lighter and easier to move about than the 6. I almost went with it, even had it in the cart, but decided at the last minute to go for what I figured would give me enough aperture for a lot longer shelf life.

    Looking forward to your thoughts and comments on the SkyScanner 100.

    Doug


  5. Hi Matt,

    Your recent posts, this one and the following one on aperture, are timely indeed. Just recently I decided that I really want to have a new, larger, scope by next summer. Ideally before the Golden State Star Party. I’ve been giving a lot of thought to the trade-offs inherent in any telescope purchasing decision. Building spreadsheets to track candidates and designs. I even started a blog at http://oneyearonescope.blogspot.com to collect and share my ideas.

    Price per square inch of aperture was not one of the figures I was keeping track of, until now. Calculating it for my current leading candidate, a 16″ scope with JMI mirror built into a dobstuff.com kit, I come up with $14 per square inch. Looks like the costliest scope on your chart! It gives me pause and might cause me to re-consider some of my decisions. Particularly in light of the 16″ Meade Lightbridge at $10 per square inch.

    Looking at your numbers I am a bit struck as to the overall trends. Rather than getting cheaper per square inch as the aperture increases, it seems to get more expensive. Doing a quick calculation on the Obsession 18″ (admittedly a luxury scope, but it’s tough to find options in that size) comes out to a whopping $27.50 per square inch. I think it just goes to show the challenges inherent in producing a large, well figured mirror, and the structure to support it.

    Thanks for another enlightening post!


  6. If someone didn’t have $100 to spend and was leaning toward the FirstScope, I would instantly recommend that they instead opt for the 15 x 70s. Sometimes I go out for an hour with them and just lie back and look around.

    If I could only have one instrument, it would be the XT10. But if I could have two, they would the XT10 and the 15x70s. They’re actually very complimentary, and for some of my greatest observing runs I have used only these two. Sort of like the 48-inch Schmidt camera that served as survey instrument for the 200-inch Hale telescope, the 15x70s give me a lot of deep-sky punch with the freedom of rolling unmounted, and let me work out star-hops and find the brighter objects before I even try for them in the XT10. There have been times that I have gotten out to the desert, set up the XT10, and spent two or three hours cruising around with the 15x70s instead. They gave me my first views of the North American Nebula and the Veil Nebula and of countless clusters and asterisms in the winter and summer Milky Way. Give me a picnic table, a sleeping bag, a pillow, and my 15x70s, and I will be happy for a long time.

    It took me a surprisingly long time to realize this, but I think the sheer existence of the 15x70s is why I haven’t warmed to the TravelScope 70. I know other people have been able to push theirs farther, magnification-wise, but mine really throws up the most pleasing images under 20x. And if I want a low-power 70mm view, I might as well get one for each eye and ditch the tripod. It’s an amazing instrument at an amazing price.


  7. Hi Richard,

    Welcome to 10MA! I just read all your blog posts. I love hearing about how people came by the gear that works for them, and I love speculating about dream scopes, so your blog is squarely in my interests. I’ll add it to my blogroll as soon as I get this comment posted.

    Calculating it for my current leading candidate, a 16″ scope with JMI mirror built into a dobstuff.com kit, I come up with $14 per square inch. Looks like the costliest scope on your chart! It gives me pause and might cause me to re-consider some of my decisions. Particularly in light of the 16″ Meade Lightbridge at $10 per square inch.

    Yeah, but. I have read a LOT of reviews of 16″ Lightbridges that turned into lists of stuff to fix: wobbly side panels on the rocker box, painting and/or flocking all the exposed hardware, upgrading the focuser, etc. Even if one has the time and mental energy for all of that, the costs rapidly erode the per-square-inch advantage.

    FWIW, my own dream scope is a 14″-16″ light dob, and I’m really leaning toward the DobStuff. I want the biggest scope I can afford that breaks down well for travel–I will probably never have the freedom to base my automobile purchases around my telescopes–AND that won’t kill my back; 50lbs is about as much as I want to move at once. For a long time I was thinking about the 14″ TScope, but the DobStuff is a little more affordable and at least as portable. Either option will require saving considerably more than Orion’s XX14i, but damn, that beast weighs about twice as much, and even the mirror bucket alone weighs more than the complete assembled TScope. I expect that this next jump will be my “lifetime” scope, and as long as I’m saving for a few years for a scope I’ll hopefully use for a few decades, I reckon it’s worth it to save a little longer for exactly the right scope.

    Looking at your numbers I am a bit struck as to the overall trends. Rather than getting cheaper per square inch as the aperture increases, it seems to get more expensive. Doing a quick calculation on the Obsession 18″ (admittedly a luxury scope, but it’s tough to find options in that size) comes out to a whopping $27.50 per square inch. I think it just goes to show the challenges inherent in producing a large, well figured mirror, and the structure to support it.

    Yep. And I think it’s mostly the mirror. Particle board is cheap, and you have to cut the same number of pieces to make a rocker box for a 6″ scope and a 16″ scope. Both scopes require a focuser, finder, etc., so the big one does not cost any more on those bits. But big well-figured mirrors seem to be the stalling point. An inability to consistently provide good mirrors in big sizes has killed more than one scope company and more than one scope line at companies that survived. As I understand it, the smaller mirrors (say, up to ten or twelve inches) are largely machine-made now, and only checked or touched up by an actual optician. If someone manages to automate the production of big mirrors to acceptable standards the same way, they’ll make a killing–and our dream scopes will hopefully get more affordable.

    I think a lot of it has to do with expectations rising exponentially as costs go up linearly. A poorly-figured primary mirror is a LOT more disappointing in a 16″ scope than in an 8″ scope; in a 4″ scope it might not even matter depending on the attentiveness and experience of the user. I think people expect that quality control might let a few dogs through now and then at the low end. Getting a lemon when you’ve forked out a few grand is a whole ‘nuther kettle of fish.

    And there’s one more piece to this, which is that as long as one is already resigned to forking out money in the low thousands for a big scope, there’s little reason to settle, especially since most people will only buy such a scope once in their observing careers. I can totally see someone going for a 14″ Obsession or StarMaster or whatever instead of an 18″ econo-dob (if such a thing even exists–the old Coulter 17.5s might be as close as anyone ever got).

    With all of that said, the XX14i is a pretty good deal. Yes, based on cost per square inch it is the second most expensive scope on the list, but another way to look at this is that for just a dollar more per square inch over the 16″ Lightbridge you get DSCs, a collapsible base, and better accessories. From what I’ve been able to tell, they’re selling like hotcakes. And I am sorely tempted. But I think I’m going to hold out for the DobStuff and save my arms and back. (We’ll see how my resolve holds up once my war chest gets to two grand!)


  8. Bad news – the Bushnell Ares 5 is no longer in stock. Optics Planets was the only distributor of this scope. Like the Bushnell Ares 6, which was a 152mm (true 6-inch) Dob with a 2-inch
    focuser (!!) selling for only $219.95, we will probably never see this scope offered factory new ever again. Still available in Canada and Europe as the Skywatcher Heritage 130p, but at prices way over US$200.


  9. […] But it’s the “to make it worthwhile” part that’s the kicker. As we saw in What Aperture Costs, above 10″ prices increase sharply. As long as I’m saving up for my dream scope, I […]



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