[AAVSO-DIS] Re 18024 Dobson
JBortle at aol.com
JBortle at aol.com
Fri Nov 2 12:06:55 EST 2001
I was pleased to read Jim Roe's post regarding the naming of asteroid 18024
for John Dobson. I have the greatest respect for John and have talked with
him on several occasions myself. However, while I'm sure he would accept the
honor as one of the great popularizers of amateur astronomy during the latter
half of the 20th century, I think he'd be less than comfortable to be
recognized as achieving it for telescope making. Certainly he'd say he was
not in a class with the likes of Russell Porter or many other noted telescope
The history of amateur astronomy and telescope making seems to be all but
forgotten by each succeeding generation. Great observers and optical
innovators in the hobby are often forgotten even within their own lifetimes.
So it is of little surprise that designs and techniques that are resurrected
after a few decades are looked up as new concepts. The Donsonian telescope is
certainly one of these instances.
As John is the first to admit, there was nothing new about the way he built
telescopes - save perhaps for his use of very inferior glass! The "Dobsonian"
design was in use prior to 1850 and widely employed in commercial English
telescopes during the second half of the 19th century in less expensive
"garden telescopes". In fact, the alt/az trunnion design owes its origins to
permanent heavy gun mounts! To be sure, the material used in the earlier
(19th century) telescopes was steel and iron, so that their mass required
turning via the use of gears. Dobson simply substituted plywood, inspite of
its comparative flexibility, for all the heavy components, allowing the
instrument to be moved by simple hand pressure. Still, the design was
unchanged from the original seen in 19th century catalogs.
Likewise, the mirror support system used in Dobsonian scopes is identical
with that employed by many optical firms to support large mirrors during
testing well before 1950, so the support strap holding the mirror was nothing
new. And the mounting of the secondary on the early Dodsonians gave
experienced telescope makers nightmares, rather than being inovative!
When I was growing up and a newcomer to astronomy, amateur-made telescopes
had to be finely machined, elaborate contraptions, often requiring several
men to set up if larger than 10-inches in aperture. The alternate was a light
pipe fittings mount that carried too large a tube and that was scoffed at by
the "real" telescope makers of the day. Be assured, had John Dobson come to
Stellafane in the 1950's or early 1960's with one of his scopes he would have
been laughed off the telescope field. If by some miracle it had been judged,
the scope would have rated far to flimsy, unstable, and unworkmanship-like to
have been taken serious note of.
Interesting how things changed!
John Bortle (BRJ)
More information about the Aavso-discussion