Expert: Paul Wagner - 1/28/2006

Question
Hi!
I got a Present, a "Meade 290c" but no instructions.Can You please help me?
It says on it 3x and d 60mm and f 900mm
only one Eye peace. The Lens on it is very
small. Should I change the Eye peace?
What does d6mm and f900mm stand for?
Thanks very much Yours truly
John Nagel     jjn@golden.net  

Answer
HI John:

I can explain some of this...and some you may have to give me a bit more information.  d60mm means that the diameter of the primary lens ( the one you point to the sky) is 60mm in diameter--a little over two inches.

The f900mm means that the focal length of that lens is 900mm, or about three feet. That's very typical of this entry-level scope.  

I am afraid the the final figure, the 3x, has to do with a barlow lens.  This is a special lens that fits into the scope where the eyepiece goes...but also has a fitting on the outside end for the eyepiece itself.  

With a normal eyepiece of 25mm or so, this scope will give a magnification of about 36X.  That's a nice power to look around the sky and find some of the larger objects.  At that power, the moon will fill up about half of the eyepiece field, and you will see some nice detail.  If you use the barlow lens and insert the 25mm eyepiece into the outside end, you will triple your power, to about 100X.  The will show the rings of Saturn quite easily, and the atmospheric belts on Jupiter.  

If you don't have another eyepiece, I would look for something simple.  This is not a top level scope, and my guess is that the diameter of the eyepiece tube is about 0.965 inches---that's standard for smaller scopes...but more serious scopes use 1.25 inch diameter eyepieces.

You might find something you can use on ebay, or here:

http://www.surplusshed.com/

Don't spend a lot of money on this---if you really get interested in astronomy, you will want a bigger scope...and those larger sized eyepieces.

Paul Wagner