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How to Use Telescopes : Telescope Eyepieces


So, when you first purchase your telescope,
it’s likely going to come with about two lenses. These are the typical lenses, that most of
the good quality telescopes will come with. This one is a twenty six millimeter eyepiece.
This one is a nine millimeter eyepiece. Now, the numbers that you see on the side, those
focal links. That will ultimately tell you the magnification that you’re going to be
using, when you insert one of these into your telescope. To figure out the magnification,
when using any eyepiece. You simply have to divide the focal length of the mirror, or
the lens in your telescope, by the focal length, of your eyepiece, and that simply gives you
the magnification. So I have a couple of other eyepieces here, and there’s a couple of things
that you can notice. Well, first off, there all in order of ascending focal length, so
this is our nine. This is our twenty six. This is our forty millimeter, and this is
a fifty five millimeter, so for the most part, when eyepieces get higher in focal length,
they usually get larger. That’s not always the case, but typically, that’s the trend.
That also means that when you have these really high focal length eyepieces, you get a much
wider field of view, because the magnification has decreased quite a bit. Now, a lot of people
may think, well, I want a high magnification, to where I can see objects in the sky, up
close. When you do that though, you end up getting a much more blurry image, and also
the image decreases in brightness ,so some of the best views, are through the really
wide eyepieces. The drawback though, is that when you get really high, or really low magnification
eyepieces, you really start increasing in price. So typically, these starter eyepieces
are in the tens of dollars of range, so they may be thirty to fifty dollars. They’re really
good quality eyepieces. They use, let’s see here. This Plossl uses about four lenses in
it, to give a very good quality image, but then you get eyepieces like this fifty five
millimeter Plossl. It actually has a much wider field of view, but it also has a much
higher price tag. Something like this will run about five hundred dollars, so they’re
not required for first starting out, and a strong mea, and observing with the telescope.
But as you gain experience, you may want to think about getting other eyepieces. There
are alternatives, though, to achieving different magnifications, but without getting different
eyepieces. One type of lens that I use, is called a Barlow Lens. This simply allows you
to insert one of your eyepieces into the end, and then you insert the entire apparatus,
into the telescope. It just has a lens doublet down at the end, and when you insert this
in front of your eyepiece, it effectively, increases the magnification, because it actually
increases the focal length of the telescope, itself. And so if you go back to that formula,
you increase your focal length of your telescope, then you increase magnification. Now, these
come in quite a few different varieties. You can get, this is a three times Barlow, which
means that it will effectively triple the magnification of your current eyepiece, and
then you can get the smaller versions. This is called a shorty type, and this one, it
magnifies the lens magnification by twice, by two times. Now, on the other side of the
spectrum, if you want to gain an even wider field of view, you can get one of these. This
is called a focal reducer, and this, like the name implies, reduces the focal length
of the telescope, which means that it decreases the magnification ,so you can get these to
fit on your specific type of telescope, and they provide really good fields of view, and
they can bring down your magnification by two times, three times. It just depends on
the lens itself.

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