Telescopes: To Build or Buy?

A purely pragmatic look at the cost of doing it yourself.
The post Telescopes: To Build or Buy? appeared first on Sky & Telescope.

Equipment: Guides & Recommendations

Telescopes: To Build or Buy?

By:

Jerry Oltion

February 20, 2026

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A purely pragmatic look at the cost of doing it yourself.

Jerry Oltion

In the early days of amateur astronomy, if you wanted a telescope, you built it yourself. Commercially manufactured telescopes were few and far between, and those that were available were horribly expensive. Often, they had to be commissioned as one-off, hand-built items. Even when companies like Edmund Scientific started selling budget Newtonian reflectors, the cost was still well beyond most families’ budgets.

On the other hand, the price of a glass blank and some grit was fairly reasonable, typically a few dollars for a 6-inch mirror. Once completed, the mirror could be chemically silvered (not aluminized) for a few dollars more. Adding a cardboard tube got you an optical tube assembly (OTA), some pipe fittings got you an equatorial mount, and with a Ramsden or Huygens eyepiece for a few dollars more you were in business.

*BUILT WITH CARE A home-built 8-inch Dobsonian telescope can rival a commercial scope in quality, usability, and price.
Jerry Oltion*

John Dobson revolutionized both the size and ease of mounting homemade Newtonian telescopes, bringing scopes as large as 24 inches in diameter well into the realm of possibility for amateur telescope makers. But commercial telescopes remained wildly expensive: A 6-inch f/8 Newtonian went for $228 in 1971, which is $1,466 in today’s dollars.

This situation persisted well into the 1970s, mostly because nobody could come up with a decent way to automate the mirror-making process. Paying someone in a telescope factory to grind a mirror was way more expensive than doing it yourself (assuming you worked for free).

[commercially manufactured telescope vs DIY | Sky & Telscope]

DECISIONS, DECISIONS . . . The price of a commercially manufactured telescope has never been more affordable. But is it still cheaper to build your own rather than purchase a scope outright?

Then the Coulter Optical Company came along and started selling medium-large (10′′ and 13.1′′) Dobsonian reflectors for only a few hundred dollars. Suddenly the equation flipped, and it became cheaper to buy than to build. Or nearly so, depending on how much scrounging of parts you were prepared to do.

Coulter’s mirrors were hit-and-miss, though. Some were very high quality, others not so much. If you wanted a truly excellent mirror, you were still better off making it yourself.

However, Coulter opened the floodgates. By the turn of the 21st century, multiple other companies had joined the fray. Their increasing technical expertise raised the quality of their mirrors until nowadays it’s relatively rare to get one that isn’t at least quarter-wave accurate, what’s often called “diffraction limited” (which means theoretically it can’t get any better, although you could probably start a bar fight if you insisted that was true around more than a couple of other astronomers).

[Orion SkyQuest XT8 Dobsonian telescope | Sky & Telescope]

*STIFF COMPETITION The Orion SkyQuest XT8 Dobsonian telescope is our benchmark. It’s an economical model whose price is tough to equal, much less beat.
Orion Telescopes & Binoculars*

So, what’s the story today? Can you buy a good telescope cheaper than you can build one?

I can show you how you can make your own 80-mm refractor with a factory-made lens and focuser, some galvanized flashing, and an oatmeal canister. Total cost is about $60. That’s considerably cheaper than what it would cost to buy a complete 80-mm refractor. But an 80-mm scope isn’t really enough for a serious amateur astronomer. Most of us will quickly lust after something more.

The 8-inch Benchmark

An 8-inch Dobsonian is arguably one of the most versatile telescopes in existence. It’s easy to transport, yet large enough to show you some serious eye candy. As I write this in June of 2021, Orion Telescopes & Binoculars (telescope.com), Sky-Watcher (skywatcherusa.com), Zhumell (zhumell.com), and several other companies will sell you a very good one for about $450. This is more than usual due to the surge in demand brought about by the stay-at-home orders during the Covid-19 pandemic, but it’s still pretty reasonable. So $450 is our target. Can we make an 8′′ scope for that? Let’s have a look at the numbers.

*NEWTONIAN ESSENTIALS The primary and secondary mirrors are the heart of a reflector telescope.
Jerry Oltion*

The Primary Mirror

The heart of every reflecting telescope is its primary mirror. All else is, well, secondary. And it’s pretty much a given that if you’re going to make your own telescope from scratch, you’ll want to grind your own primary.

To start with, you need a piece of glass. The cheapest blank I can find online is from Got Grit (gotgrit.com) and goes for $55 when it’s in stock. That’s for 3⁄4′′-thick plate glass, which is perfect for an 8′′ mirror. In the old days the rule of thumb was that your glass should have a thickness of one-sixth of its diameter to avoid sagging due to gravity, but that has proven to be overly cautious; 3⁄4′′ is plenty for an 8-inch mirror.

An 8-inch grinding kit from Got Grit provides you with all the grit, pitch, and tool supplies you’ll need, and it currently costs $64. So you’re out $119 to get started.

Anywhere from 40 hours (if you’ve done this before or if you’re lucky) to 100+ hours later (if you’re fussy and/or over-zealous in the final figuring like I am), you’ll have a parabolized mirror ready to be coated. Several different companies offer vacuum-deposited aluminum coating services, which is the standard telescope mirror coating nowadays. (A list of companies that provide the service appears in our March 2019 issue, page 38.) Their prices for an 8-inch mirror average about $100. Shipping both ways is about $50 more. The adventurous might consider silvering their own mirror for a bit less (S&T: Jan. 2020, p. 74), but let’s assume you’re having yours aluminized. So now we’re up to $269, and we have a shiny primary mirror in hand.

Interestingly enough: You can buy a completed 8′′ f/5 mirror for about $240. Add in shipping costs and it’s a wash. Arrgh!

The Secondary Mirror

I have a mirror-making friend who says he doesn’t hate anyone enough to teach them how to make their own secondary mirror. Grinding and polishing a truly flat mirror is way harder than making a parabola. So, most amateur telescope makers simply buy them.

The size of the secondary depends upon the primary diameter and the focal ratio of the scope. F/5 is a very common focal ratio for an 8′′ scope, so let’s assume that’s what we’ve ground our primary mirror to. The diameter of the secondary mirror is also heavily dependent upon how far from the optical axis your focuser sticks out, but it’s common practice to add 3.5′′ to the radius of the mirror (4′′ in this case) to account for the focuser’s average travel. A little math (secondary diameter = centerline-to-focal-plane distance divided by focal ratio) tells us we need a 1.5′′ secondary mirror (3.5 + 4 / 5 = 1.5). You can buy secondary mirrors from many vendors. The average price I’ve found for a 1.5′′ is about $40.

We’re now at $309.

The Optical Tube Assembly

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