It might interest some to know that John Dobson is still around (I
know this because he was taking his morning walk by my house the other
day) and he still travels around the country teaching folks how to
grind their own mirrors, make telescopes, etc, using mounts that look
just like your link. The tubes are from cardboard concrete forms.
Dobson recommends you take apart a pair of pawn shop binoculars to get
You end up spending a few hundred dollars to construct a scope that is
better than any you could purchase for thousands.
The plans on the web site appear to be scans taken from his
instructions that he passes out when you make a scope in his class.
: You end up spending a few hundred dollars to construct a scope that is
: better than any you could purchase for thousands.
I'm willing to think that a few hundred dollars could
make for a nice scope, with some serious work involved. But how do
you know it would be better than anything someone could produce
in a factory for ten times the money?
-- Andy Barss
If you grind your own mirror, which in mho is the hardest part - the
woodworking is pretty basic - there is the possibility of getting a
mirror with much greater accuracy than can be purchased for a similar
Also, with attention to detail and design, other parts of the scope can
be improved upon over the typical import scope.
Yes, it is possible to buy a mirror blank and turn it into a mirror
worth thousands, and I think this is what the op is referring to. For a
few hundred dollars in total parts, you can actually make a scope worth
perhaps a couple of thousand.
Perhaps if the word 'can' were inserted...
"You 'can' end up spending a few hundred dollars to construct a scope
that is better than any you could purchase for thousands.'
depends on how well you grind your mirror and to a lesser extent, how
well you build the rest of the scope.
I took John Dobsons class and have a great telescope that I take up to
the intersection by my house a few times a year. Not only was it
relatively inexpensive, but it is indeed a great telescope.
Fortunately we have a number of used record stores in and around the
Haight Ashbury - I was given an old scratched LP by one for the bearing
surface on the base that allows the device to rotate smoothly through a
complete circle. I used UHMW jig/fixture material for the other bear
surface, although in John's class they do supply small teflon pieces. I
had to try the UHMW as we sell it - it worked as well as teflon.
As I recall the entire device is generally called a Dobsonian telescope
because John Dobson devised a fantastic design that could be built
cheaply by almost anyone. The optics have been around for a long long
By the way, the telescope is a great people magnet. Even in my
residential block - perhaps six to eight blocks from the real heart of
the Haight-Ashbury - I will have ten to twenty people stop by to ask
what I am doing. When they find out, they invariably ask if they can
view. My eight inch telescope fills the eyepiece with the moon, and when
it is full the light is almost blinding. The rings of saturn are
incredbile as well. My wife also agrees that more than half of those
that stop are single women, so if one were single ... well I'm not.
The mount took perhaps a day's work, the mirror much longer. At the very
end of the grinding and polishing John did help with some slight
problems I had, using a trick he had only figured out in the relatively
I didn't see the start of this tread, but I would highly recommend
making one of these - fun, educational, and a gift to the community when
you share the night sky with them.
========================Astronomy is another of my Hobbies...
"my" Observatory is finally under construction as the Dome itself was
finally delivered last week...thus my SCT will finally have a home and
I will not have to contend with cooling down the scope before putting
my eye to the eyepiece.. and dew will become a "little" less of a
I have to admit however that I never attempted to grind my own mirrors
or build my own scope... BUT I have had the pleasure to let some of
the neighborhood folks look at Saturn and hear their reactions (WOW)
And a couple of local teens stop by almost every time I set up
Clear Skyies to y'all
Years ago (don't ask) I ground, posished and figured a 10"
Newtonion reflector, f7.2. Whenever we had guests over when
I had the telescope set for viewing Saturn they would stand
on a picnic bench and look down the tube to see if I had set
up a fake picture or something in the tube to fool them.
They could't believe the image was so impressive.
Yes, 'can' is quite apropos. However, you _can_ also buy the
optics and make a scope that resolves fine detail and has a much
lower limiting magnitude than a store bought or mail-order scope
costing several times as much.
The simple mount developed by John Dobson is smoother than
what you will get in any scope for less than $1000 and can be
made for the price of a cople of sheets of plywood, a handful of
a bit of glue and paint and some formica and plastic scraps.
To be accurate, his altazimuth mount was never intended to
be mechanically driven in the first place, nor were his scopes
intended for photography.
Howver, you can plop the whole scope down on a Ponce' platform,
which traditionally is built as a constant speed one-axis drive.
Your exposure times wil be limited by considerations of balance
and travel in the drive mechanism
On Sun, 16 Jul 2006 02:49:58 +0000 (UTC), Andrew Barss
Hmm, I was paraphrasing Dobson there, and I trust that he knows.
Better optically, per inspection and correction of the primary mirror
using a technique of using a bright point of light and out of focus
eyepiece to obtain an interference pattern image at the eye; from that
hand corrections are made to the primary mirror until the interference
pattern is "correct". Commerically made mirrors don't approach the
precision of this method until you get into the big bucks.
Again, paraphrasing Dobson.
A lens or mirror cannot be molded to any better standards than it can be
ground (in any process that I'm aware of). Chances are that the molded
product would be inferior as it can be no more accurate than it's mold and
likely less so.
Significant advances in molded optics have produced optics of very high
precision, but nothing yet at the precision of ground optics.
Note that the answer to original question, that for several hundred
dollars in parts, one can produce and optical system worth many thousands
of dollars. This is the equivalent to the fact that with several hundreds
of dollars worth of wood, one can produce furniture that would cost many
thousands of dollars. The only thing standing between the wood and the
furniture is many hundreds of hours of labor and some quality woodworking
tools. Same thing holds for the telescope. If one's time is free, yes, a
few hundred dollars of components results in something that they would have
to pay thousands for. But most likely, one will have put several thousand
dollars worth of hours into the project.
If you're gonna be dumb, you better be tough
If I recall correctly, with Dobson teaching the class (he can be a
very crabby guy, by the way, but he very much believes in what he is
doing in helping people learn astronomy and how to do their own
scopes) the investment in grinding and polishing your own mirror and
building the scope and the mount is something like 20-50 hours. I did
this about 10 years back with an 8" mirror, so I don't recall the
total hours that well. Most of the class did 10" mirrors and their
grinding time would be a bit more.
If I was a consultant, I guess I would be earning about $100/hr in my
chosen field (not astronomy) and so I guess I lost money on the deal.
But I had fun.
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