What type of lens should I buy for my telescope?
Mommy to Sammy asked:
I just got it and cannot get it to see the stars or the moon. It came with a 10mm and a 20mm. I took it on vacation with me and can see other things through it such as the ocean across the street (about 350 yards from where I am staying) and other things, but not the moon or the stars. What mm should I purchase? Can any lens really work, or do I have to go by the name of the telescope? I didn’t know if they were universal.Thanks in advance.
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I just got it and cannot get it to see the stars or the moon. It came with a 10mm and a 20mm. I took it on vacation with me and can see other things through it such as the ocean across the street (about 350 yards from where I am staying) and other things, but not the moon or the stars. What mm should I purchase? Can any lens really work, or do I have to go by the name of the telescope? I didn’t know if they were universal.Thanks in advance.
November 26th, 2009 at 11:34 am
Your question really has me puzzled, as I cannot understand how a telescope can show you things like the ocean but not the Moon. It would help if I had a better idea of what kind of telescope this is: aperture (diameter of main lens or mirror), focal length and type (refractor or reflector).
If you can see the ocean, and bring it into sharp focus (by turning the focusing knobs next to the eyepiece), you should equally well be able to point it at the Moon and focus it on the Moon. Is the problem that you can’t point it accurately? The field of view of an astronomical telescope is very narrow and it must be pointed accurately; most telescopes come with a finder of some kind. The finder must be aligned with the main telescope by pointing the telescope at something at least a quarter mile away, and then, without moving the main telescope, adjusting the screws on the finder so that it is pointing at the same object. For all of this, use your telescope’s lowest power eyepiece, the 20mm.
The Moon should look like the Moon, only larger. The stars will look just like stars; no amount of magnification makes them any larger. Take a look at Jupiter: it’s the bright object in the south at twilight, moving into the southwest later in the evening. It should appear as a tiny disk with three or four tiny “stars” alongside it. These are its moons.
[Edit] I forgot to answer the second part of your question. Most telescopes use standard size od eyepiece 1.25″ in diameter. You shouldn’t need to buy another eyepiece because the 20mm and 10mm eyepieces should work just fine. Geoff G
November 29th, 2009 at 1:10 am
Huh? Can not see the stars or the moon? Then return the telescope!
The stars will look as dots what ever magnification you have. That’s because they are so far away. The moon you can see with your own eyes. So if you can’t see it through your telescope it must be broken. Enough ranting.
The magnification is the focal distance of the objective lens divided by focal distance of the ocular lens so if you want larger magnification you’ll want a smaller focal distance of the ocular. That is less than 10mm. And if you want less magnification you’ll want more than 20 mm.
Be aware however that really large magnifications are not really useful because of motion blur because of the moving atmosphere.
Also the moon is a rather bright object. You might want to consider a filter to dampen the light somewhat. Robert E
November 29th, 2009 at 12:05 pm
Sounds like you need to align your finder,If you can see things during the day you should have no problem looking at the moon.
The 20mm and 10mm eyepieces should be all you need for now.Most telescopes now days(it would be helpful if we knew the brand and Model of yours)use 1.25″ or 2″ eyepieces and can be purchased from many different company’s.
Wally wallyrush