Expert: Tom Whiting - 9/15/2006

Question
Thanks for the great help Tom, I did some searching and found this..

http://www.sportchalet.com/product/index.jsp?productId=1973380&cp=2011119.201521

Do you think it might be worth a try or a piece of junk?  Thanks again!
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Followup To

Question -
Hi Tom,

I have a tasco 302012 reflector and haven't used it in a while.  I am trying to find an eyepiece that will reverse the light coming in so I can see things as they are when i go up on the mountains.  Do you have any websites of these types of eyepieces that will fit my scope? Thanks so much!

Phil

Answer -
Hi Phil,
Sorry, but I am not familar with that 302012 designation,
but I do know that the device you are seeking is called
either an "image erector" or "correct image star diagonal".....
I googled "image erector" and came up with what looks like
some good deals, most costing between $40 and $50 USD.  See
http://www.astronomics.com/main/Image_Erecting_Prisms.asp/catalog_name/Astronomi

Problem is that most of those devices only come in 1.25 inch barrel diameter....so if your Tasco uses the old Japanese  0.965 inch eyepieces and barrel diameter, you may also have to purchase an adapter...same if your Tasco is a standard 2" barrel, but I don't think I've ever seen a Tasco scope that
employs a 2 inch diameter eyepiece barrel.

My personal pick would be the Orion (OrionTelescopes.com)
Correct-Image star diagonal for $39.95 + shipping.
I've always had great service and luck from my eyepieces,
most of which I ordered from the Orion Catalogue.
(Page 63 in their latest Fall 2006 catalogue).

Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA  

Answer
Hi Phil,
Well, that low price tells me that it would be ok for
terrestrial viewing only (not astronomical) because the
wavelength requirement for terrestial objects is a lot lower
than astronomical objects.  But I think you told me that that
was all you wanted it for.
I would not trust it for night sky viewing though, because
at that price, I highly doubt that it is ground and figured
for 1/8 or 1/10th (or even better)  wavelength of light (2 millionths of an inch, or better)....it's probably figured for either 1/4 or 1/2 wave (10 millionths of an inch, or worse)...which is not acceptable for astronomical viewing.
(Thus the very low price).

That's why we recommend more expensive astronomical
equipment....for the night sky, the toughest thing to do is
keep a pin point star....a pin point of light.  (Rather than
a comma, sea-gull wings, a fat blob, etc.)   In effect, all light
must come to a common point focus, and only 1/8 wave, or better, figure will do that (it's called resolution).
{That's why astronomical equipment is so expensive...you
are paying for that exquisite grind and figure...so all the light
comes to an exact point source, otherwise one has a
"piece of junk"....that's why we never 'scrimp' on telescopes
for the night sky....you either go first class, or you don't
go at all. }  In fact, to be honest with you, we never recommend Tasco scopes for night sky astronomy,  because most are only ground to 1/4 wave, or worse,....thus the low cost.  (Accompanied with poor image resolution).
We don't even recommend Celestron or Meade anymore,
because of their low optical quality.  (Although the older
models are very good...built before 1995).
Top names now, for exquisite grinds, are Antares, Orion, Hardin, and Discovery 6- 12 inch scopes, for the 'beginners'
which are in the $500 to $1000 price range.
($500 is the minimum you want to spend on a good scope....
sorry, but just the laws of optics with their required
1/8 wave, or better,  figures).
But for just terrestrial viewing, the lower priced brands
do just fine. - But don't ever buy a Tasco (or any 'department
store' scope)  for the night sky...they just don't work.
(Except for the moon, of course, but it's more equated to
a terrestial object as opposed to a night sky object).
The moon view is not a good test for a telescope.

{Try to split a double star, like the Epsilon Lyrae
Double-Double..... that is only 2 arc-seconds of
separation- that is an excellent optics test.}  Because it takes high resolution to do that.

Hope I've been of some help here, and for further discussions,
please feel free to contact me directly at
bwhiting@velocity.net
Clear skies,
Tom Whiting
Erie, PA