Expert: Tom Whiting - 7/4/2004

Question
Hi!

I currently own a 4.5 inch reflector telescope with 900 mm focal length. Is it worth it upgrading to a Celestron 6 inch reflector telescope with 750 mm focal length? I live in a suburban area with moderate light pollution. However, I will definitly travel from time to time since I have not tried to do so yet. But I will be using my telescope 90% of the time in my backyard.

Thank you very much!

P.S. Is a refractor better for looking at DSOs in a light polluted sky? I was just wondering...

Answer
Hi Deeb,
Well, you actually have two separate questions...size of
scopes and light pollution; the two are NOT related, as
any scope is practically useless no matter what the size,
in heavy light polluted conditions.

(An old astronomy phrase worth memorizing)
You can always substitute a scope with a bigger scope,
but there is NO substitute for clear, dark skies.

(Even my 30 inch portable DOB is practically worthless
in the downtown Erie, PA area).

Ok, at the smaller apertures, say 12, 14 inches and less,
your best advantage rule is to *double* your aperture with
a new scope, so it would be much better and more efficient for you to go up to an 8 or 10 over a 4.5, rather than just
a 6 inch.  (Unless you are considering a high quality expensive 5 or 6 inch refractor).  If you go to an 8, then your next jump will be a 14 or 16 inch.....after 14, you want to make at least 6 or 8 inch jumps after that. I went 6, 8, 13, 18, 24, 30 over my 40 years in astronomy.
(All Newtonian reflectors as my speciality is DSO's only)  But if I had it to do over, I would have skipped the 8 inch size.  8 inch is a nice gain over a 4.5, but not that much over a 6 inch diameter glass.

Refractors are never good for DSO's (relative to large
DOBS) in either a dark, or light polluted sky.  Refractors are primarily made for splitting close doubles, and detailed lunar/planetary work....I've seen 5 and 6 inch refractors equal or even beat out my 30 inch on planets and moon, but of course I blow them away on DSO's.

Telescopes are kind of like airplanes; all airplanes fly,
but you don't normally send a fighter to do a bombers job.  Using a refractor on DSO's is like sending a fighter to do a
bombers job.  Perhaps now is the time for you to decide
WHAT you want to specialize in....lunar/planetary observing
or DSO's (or comet hunting, variable stars, asteroids, etc)
There is a scope out there that maximizes each of those activities, so decide what you favorite specialty is, and go for that kind of scope. (You can't have it all, unless you have the money to own various types of scopes...ie- more than one scope.)

Also, be advised that Celestron and Meade used to be top
names in high quality mirrors, but not any more...Meade
went public so they have to please their stockholders
so their optics have go way down hill....Celestron went
bankrupt and were bought out by Trashco (Tasco) and we all
know how horrible Trashco scopes were even before they bought out Celestron.
Your top optics names now are Orion, Discovery, and Hardin,
the latter is the new kid on the block, and thus have the
best optics because they are trying to establish their name
for themselves...(See any Sky & Telescope recent magazine
for their addresses and phone numbers and ads, or use
the internet).

If you decide on a larger high quality refractor, then
I don't know, never having owned one...although I have looked thru the Celetron and Meade 4 thru 7 inchers, and
the optics quality is quite nice.

Of course, with a large aperture DOB, you can 'cheat' and
put in an aperture stop to simulate the same effects as a
refractor; eliminate any central obstructions...it really helps but does not completely duplicate the fine qualities of an expensive refractor, but it comes close. This is
an option you do not have with a refractor type scope.
So with a large DOB, you can have the best of both worlds.
(For instance, I have a 30 inch piece of cardboard with an
11 inch off-axis hole, so I can cut the 30 f4.5 down to an
11 inch f12.3 for lunar/planetary work.)

So, in conclusion, I would double to an 8 or 10 inch,
decide what you want to specialize in, and do like I do
on weekends....travel to darker skies to avoid the light
pollution.  In fact, we are going over to Cherry Springs
State Park- 2nd darkest skies East of the Mississippi, on
the new moon weekend of July 16, 17....that's 15 miles
SE of Coudersport, PA where camping for astronomers is free,
but no white light allowed from dusk to dawn, because it is
now a designated Dark Sky PA STate Park..only one in the state.
Clear Skies,
Tom Whiting
Erie, PA