Sky & Telescope - November 2021 - 69

have to settle for a 4-foot length of 10-inchdiameter
tube, which will cost you about $11
at just about any home improvement store.
So now we're at $320.
You'll need something to hold the secSCAVENGED
OCULAR A binocular eyepiece works
just as well in a telescope as it does in binoculars.
ondary mirror in the tube. That's called the
" spider, " and it's usually made of four vanes of
metal and a 45°-angled mirror holder. You can
make your own out of hacksaw blades, metal
rulers, strips of galvanized tin, or even - harkening back to the
days of Dobson's original sidewalk telescopes - cedar shingles
(S&T: Apr. 2020, p. 36). I make mine out of wire nowadays.
You can also buy one. There are several vendors and the
prices range pretty widely, but a spider for an 8″ scope will
cost you about $40 to $100. To heck with that! Let's assume
you've got some hacksaw blades or shingles and some ingenuity,
so your spider will cost you a whopping $5.
That brings us up to $325.
You need something to hold the primary mirror at the
bottom of the tube and let you collimate it. You can spend
as much as you want to on a mirror cell, but with a ¾-inchthick
primary you can make your own out of plywood, some
cork or hardboard padding, a triangle cut out of a cereal box,
and three bolts (S&T: Apr. 2020, p. 72). Assuming you do it
that way, your cost is only another $5.
We're now at $330.
Coming into Focus
You'll need a focuser, too. A good two-speed Crayford will set
you back anywhere from $150 for the decent
ones made by Guan Shen Optical (GSO),
to you-don't-want-to-know for a precision
high-end model. If you buy the GSO focuser,
that puts your total cost at $480, which
(buzzzzzzzzzzzz!) puts you over the cost of
the commercial scope. So guess what: You're going to have to
make your own focuser.
Fortunately, I showed you how to do that in the February
2015 issue (page 68). Materials will cost you about $10, or a
little less if you or your significant other knits and lets you
repurpose a knitting needle to use as the focuser's pinion.
We're now at $340.
A commercial scope usually comes with at least one
eyepiece - usually a 20- or 25-mm Plössl. You can buy one
from Orion for about $40, or you can make your own like I
described on page 74 of the September 2020 issue. That design
used lenses from Surplus Shed (surplusshed.com), which cost
$8.50. Then again, you can do as John Dobson did and buy
a pair of binoculars at Goodwill and rob the eyepieces from
that. That'll probably cost you about $10. So, let's go with the
$10 figure, bringing us to $350.
Of course, a telescope of this size needs a finder. A Rigel
QuikFinder would be really nifty, but that'll set you back $46
at Scopestuff (scopestuff.com) and even more elsewhere. Better
build your own finder. I've described several different ways
sk yand tele scope .o r g * NOVEMBER 2021 69
http://www.surplusshed.com http://www.scopestuff.com http://skyandtelescope.org
Sky & Telescope - November 2021

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