Explore Scientific TWILIGHT Series, Manual

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EYEPIECES
MAGNIFICATION
One of the main roles the eyepiece plays is setting the magnification or power of a
specific optical set-up. The amount of magnification you will want to use depends largely
on your subject. To calculate magnification, divide the focal length of the telescope by
the focal length of the chosen eyepiece. The resulting number will be your power. For
example, a 20mm eyepiece in a telescope with a 1,000mm focal length will result in 50x
power, which will make the object appear 50 times larger. If you change the eyepiece,
the power goes up or down accordingly. When choosing magnification, it is important
to remember that the lower the power the brighter the image. If you are observing the
Moon or a notable double star, a high power eyepiece will work well because the loss of
brightness that occurs as magnification amps up is not a huge factor. However, if you are
viewing a dim subject like an expansive galaxy or a faint nebula, you will want to use your
lowest power because you will need all of the brightness you can get. Overall, the best
way to determine what magnification level to use is to try different powers and see how
the image changes. Having a nice range of eyepieces available can be the most rewarding
way to enjoy all that the night sky has to offer.
EXIT PUPIL
The exit pupil is the diameter of the beam of light coming out of the eyepiece. To
calculate exit pupil, divide the focal length of your eyepiece by your telescope’s focal
ratio. For example, if you use a 20mm eyepiece with an f/5 telescope, the exit pupil would
be 4mm.
EYE RELIEF
Eye relief is all about a comfortable viewing experience because it is the distance at
which you need to position your eye from the eyepiece’s outermost surface to enjoy the
full field of view. This characteristic is of special concern to observers who wear glasses
to correct a astigmatism, because a long enough eye relief is necessary to allow room for
glasses. A full spectrum of eye relief distances is represented across our five eyepiece
lines.
OTHER ACCESSORIES:
FOCAL EXTENDERS
Available in 2x, 3x and 5x in a 1.25” barrel and 2x in a 2” barrel, our focal extenders add
versatility to your eyepiece line-up by allowing each eyepiece to perform at two powers.
For example, if your particular eyepiece/telescope combination results in a 50x power,
adding a 2x focal extender will change that to a 100x power. To guarantee superior
image quality, our focal extenders use multiple lens elements that are made of high-
quality glass and fully multi-coated with EMD coatings to reduce chromatic and spherical
aberrations. To use a focal extender, install it in the eyepiece barrel of your telescope/
diagonal before the eyepiece and then secure the eyepiece into it.