I'm going to take a bit of a risk ...

[creeksky (Pete)]

Originally Posted by barx1963

Pete
Yes all Newtonian scopes (a Dobsonian is a type of Newtonian) will invert and reverse the image. You get used to it very quickly.
While it is possible to setup a device that will correct this, it is very rarely done as you lose light every time you use a lens or mirror, and in the end does it really matter? There is no up or down in space!

Also with the size of the moon. Magnification is a function of the focal length of the scope and the focal length of the eyepiece. From memory these little scopes are f4 so they have a focal length of 76x4 or 304mm so your 20mm EP gives a power of 304/20 or 15x. So to make the moon image larger, you need an eyepiece with a shorter focal length, or a bigger scope!!

If you are looking at a 6" or 8", I would go the 8", not that much bigger but much more light gathering.

Malcolm

Thank Malcolm,
Yes I guess it won't matter greatly, just will be hard to learn or say to friends or figure out which lunar crators are what or which is the north south poles on Mars?
Guess I can look at maps in a mirror
Maybe an 8 inch won't even see Mars polar ice?

[creeksky (Pete)]

Skys were clear, looked at moon with 25mm alone good ,then with barlow much better and even with 4mm and Barlow incredible detail and large.
Then the frustration began,Wanted to see Mars before it set -had to move table ,chair ,scope and accessories but then a fence and tree in the way!Move again- street light and house in way gave up.
Then moved back to original position, focused on Neptune a blue ball near the size of the moon appeared, I was amazed it surely couldn't be that big with this scope?
It wasn't -turned out to be a blue LED christmas light globe grrr..
Moved again ,table chair accesories tried to resolvle Neptune best I could do was a tiny dot, not much better than the naked eye.
Then moved again, focused on Orion-sirius -worse than naked eye, plus the stars turned into light cones.
Grabbed mums old 7x 50 binos, seemed better than the scope? Except for the moon.Which this scope excelled at.Couldn't stay up for Jupiter to rise.Andromeda would have been hidden by trees.
Yes there was light polution from the moon, and a bright street light opposite.
At times frustrated moving the table and all, I nursed the bloody thing, but ofcouse too much vibration doing that.My old Tasco all those years ago seemed better?
Maybe my 54 yr old eyes can't hack stargazing any more?
Or this is really just a junk scope.Its going back-will put the money toward a 6-8 inch Dobsonian.
Surely they would be better? At least easier to move around!

[inertia8 (Australia)]

Hey Pete,

I don't think it's your eyes and it's most likely the little dob as voiced by others.

Excellent idea saving toward a 6-8" scope. As recommended before, keep an eye on the Ice Trade section for Telescopes and Mounts as they do turn up regularly from people upgrading.

Have you downloaded Stellarium (or installed the version from the cd included with the nat geo dob)?

Stellarium will give you rough approximation of what size the objects will look like with various telescopes and eyepieces.

There's a little bit of setup to be done by collecting the information required.

Start with your GPS co-ordinates for your backyard or preferred viewing sight.

Then collect the following info from the web.

Telescope:
Focal Length (mm)
Aperture (mm)

Eyepieces:
Focal Length
aFOV
Field Stop (mm)

Scroll down to Eyepieces section for more info.
http://www.stellarium.org/wiki/index.php/Oculars_plugin

Here's the User Guide:
http://www.stellarium.org/wiki/index...ium_User_Guide