[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 
makers.

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) 




 



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