ETX-105 FEEDBACK Last updated: 18 April 2005

Subject:	re: Hello. I need some Advice for Telescopes.
Sent:	Thursday, April 14, 2005 20:48:34
From:	Richard Seymour (rseymour@wolfenet.com)
You asked for the differences between a 105mm reflector and a 102mm
refractor telescope.

Look at the front corrector plate of your ETX105. See the secondary
mirror? (also known as "the central obstruction")

In 99% of reflector designs, there's that secondary mirror blocking a
measurable percentage of the light hitting the front aperture. In the
ETX 105, it's a quite reasonable (i.e. small) 9.4%

But "size" is not the only factor in the choice of telescopes.

For any given price-point, you can usually get larger or better optics
in a reflector than in a refractor.  That's because a refractor needs
more than one lens out front to be at all good. That's because light
splits into its component colors as it passes between air and the
glass.. and it takes multiple lens elements to counteract that tendency.
 Multiple elements means more cost.  Good optics means that those 
multiple elements must be all carefully ground and well-figured, often
with many surfaces with sophisticated coatings to fight reflections
between the various surfaces.

Whereas a reflector telescope just needs to bounce the light. Since it's
not going -into- the glass, reflectors don't have to have the
complicated multiple elements that a refractor has.

(if the refractor is poorly corrected for color separation, you'll see
bright targets having purple or red halos... as Jupiter sometimes does
in inexpensive refractors.)

So size isn't everything... (lack of) lens design can easily render an
inexpensive refractor almost useless for many targets.

have fun
--dick (who has an ETX90, since the 105 didn't exist when i bought it)

Subject:	Hello. I need some Advice for Telescopes.
Sent:	Monday, April 11, 2005 17:59:11
From:	Amy Spencer (v2fssap@hotmail.com)
I'm a complete amature when it comes to astronomy...umm, I did purchase
a Sky and Telescope magazine to browse through though.

I have one question however, regarding Refractors VS Reflectors. It's
generally stated that Reflectors are better because they have larger
apertures.

What would happen if both the Refractor Telescope and the Reflector
Telescope had the same aperture? EG. Approx 4 Inches. Would the viewing
quality (Image Clarity/Size) be the same?

Going further, I'd like to know if you could run a quick comparison for
me on the Meade ETX 105 AT http://www.meade.com/etx/etx_specs.html VS
the Nexstar 102 GT
http://www.astronomyonline.com.au/cache/item-1825public.html?cache=no

I look forward to hearing from you.

Thank you for your time.

Yours sincerely,
Amy Spencer

P.S. I couldn't find anyone else to E-Mail to request advice about this.
You're my only hope. *Wince*

And:

Thank you kindly for your prompt response.

I have a newly purchased ETX 105 EC, Father has been helping me to put
it together-it's quite a struggle. *Laughs* We're both very afraid that
we might break something!

Ohh, I just wanted to know if that Nexstar 102 GT Refractor Telescope
would 'out perform' my ETX 105 EC by just looking at the Statistical
data. Both are 4" but...the Refractor is actually cheaper by about
$300.00 AUD.

If you actually answered my question via the below E-Mail, then forgive
me. I'm a complete amature and must have missed it!

Sincere regards,

Amy Spencer

Feedback Archives

Check the Feedback Archives for previous editions of the User Feedback pages.

Return to the top of this page.

Go to the ETX Home Page.