10
For example, the FunScope, which has a focal length of 300mm, used in
combination with the 20mm eyepiece, yields a magnification of:
Whatever you choose to view, always start by inserting your lowest-power (longest
focal length) eyepiece to locate and center the object. Low magnification yields a
wide field of view, which shows a larger area of sky in the eyepiece. This makes
finding and centering an object much easier. Trying to find and center objects with
a high power (narrow field of view) eyepiece is like trying to find a needle in a hay-
stack! Once you’ve centered the object in the eyepiece, you can switch to a higher
magnification (shorter focal length) eyepiece, if you wish. This is recommended for
small and bright objects, like planets and double stars. The Moon also takes higher
magnifications well.
The best rule of thumb with eyepiece selection is to start with a low power, wide-
field eyepiece, and then work your way up in magnification. If the object looks bet-
ter, try an even higher magnification eyepiece. (You can purchase additional 1.25"
eyepieces, if desired.) If the object looks worse, then back off the magnification a
little by using a lower-power eyepiece.
Magnification Limits
Every telescope has a useful magnification limit of about 2x per millimeter of aper-
ture. This comes to 152x for the FunScope. Some telescope manufacturers will
use misleading claims of excess magnification, such as “See distant galaxies at
640X!” While such magnifications are technically possible, the actual image at that
magnification would be an indistinct blur. Moderate magnifications are what give
the best views. It is better to view a small, but bright and detailed image than a dim,
unclear, over-magnified image.
Using the 2x Barlow Lens
The included 2x power-boosting “Barlow” lens (see
Figure 1
) doubles the magnify-
ing power of any 1.25" eyepiece it is used with. For the FunScope, when you use
the 20mm eyepiece by itself you get a magnification of 15x. But when the 20mm
eyepiece is used in combination with the Barlow lens, the magnification is doubled
to 30x. And when the Barlow is used with the 6mm eyepiece, it yields a magnification
of 100x, instead of 50x without the Barlow.
Simply insert the Barlow lens into your telescope's focuser, and then insert the eye-
piece into the Barlow, gently securing it in place with the thumbscrew on the Barlow
lens (
Figure 6
). Then, adjust the telescope's focus wheels to enjoy double the mag-
nification of the eyepiece used.
300mm
20mm
= 15x
