Expert: Paul Wagner - 1/19/2006

Question
My husband bought a Jason Model 313 Discoverer Astronomical Telescope at a yard sale. It has the following numbers on it: F=910mm D=60mm. It has a moon lens with it. Outside the telescope you can see through it, but when you put it in the telescope you cannot see anything. Do you know what might be wrong with it? Also, are there any more lens that we need to get for the telescope? Thank you

Answer
Hi Kay:

Sounds like you have a fun project!

OK--On the telescope, please make sure you have an eyepiece.  During the day, look through the telescope at something fairly far away, and see if you can get it to focus.  The top of a telephone pole a block away is probably good enough.  

If you can do that, the telescope works, and you don't have any major problems.  The image will be upside down--that's how astronomical telescopes work.

If you can't do that, then there may be something wrong with the eyepiece.  A telescope has two lenses, the main lens captures the light and brings it to a focus.  The eyepiece then magnifies that image and allows you to see it.  You may have to go on ebay to find an eyepiece.  Make sure you get one that fits--they usually come in three sizes:  1.25 inches, .965 inches, and 2 inches.  You will need one of the first two--check the diameter of the eyepiece tube to see which one.

Now about that moon filter.  It is only for looking at the moon--and all it does is make the image a lot dimmer.  This is to protect your night vision.  If you stay out for an hour looking through the scope at dim stars and planets, and then look right at the moon with your scope---you will be just about blind for a few minutes.  That moon will seem as bright as the sun! ( It's not.  If you look at the sun through the scope, even with the moon filter, you will be blinded permanently.  Seriously.)  

So the only way to use the moon filter is to point the scope at the moon, then put in that filter. Try using the moon's shadow on the ground to get the scope pointed the right direction---when you get it close, you will actually see the bright moonlight shining out through the eyepiece.  Then slip on that filter and observe away.  With this scope, the moon is just about the best object to look at.  It has hundreds of craters, mountains, valleys and plains...

what fun!

Paul Wagner