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Calculating Magnification
The power of a telescope is how much it magnifies objects. Each telescope has its own set of focal lengths and, therefore,
different magnifications when used with various eyepieces. For example, the EclipseView 114mm used with the 26mm
eyepiece magnifies an object 17 times. The 9mm eyepiece used with the EclipseView 114mm will magnify objects 50 times.
You can calculate how much magnification an eyepiece will have with your specific telescope. Just divide the telescope
focal length by the focal length of the eyepiece.
I
Focal Length of the Telescope
÷
Focal Length of the Eyepiece
= Magnification
Look at the specifications. For example, you will see that
the focal length of the EclipseView 114mm is 450mm.
Let’s say that you have obtained a 6.3mm eyepiece. You
can tell what the focal length of your eyepiece is as it
is always printed on the side of the eyepiece. Divide:
450mm ÷ 6.3mm, which equals 71.42. Round this off
to the nearest whole number and you find the 6.3mm
eyepiece used with the EclipseView 114mm magnifies
objects 71 times.
Eyepiece’s magnification
x
2
= Magnification with a 2X Barlow lens
If you use a Barlow lens with one of your eyepieces, it
doubles the magnification of your eyepiece. Other types
of Barlows can triple or further increase the power of an
eyepiece. To find out how much your magnification is when
you use a 2x Barlow, multiply your eyepiece’s magnification
by two. For example, the 9mm low-power eyepiece used
with the EclipseView 114mm magnifies an object 50 times.
Multiply 50 by 2 and you get 100 times magnification with
a Barlow.
It’s worth repeating: Keep in mind that a bright, clear, but smaller image is more interesting than a larger, dimmer, fuzzy one. Using
too high a power eyepiece is one of the most common mistakes made by new astronomers. So don’t think that higher magnification
is necessarily better—quite often the best view is with a lower magnification value!
Expert’s Tip
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