Just Before Observing - The Accessories; Eyepieces - Omegon EQ-1 Mode D'emploi

4. Just before observing - the accessories

The telescope is standing in front of you, the main optics are on the mount and you have previously attached
and aligned the finder scope. If the sky is clear, there is now nothing standing in the way of you starting to
observe. But you do need to know a bit more about the accessories.

4.1 Eyepieces

The eyepieces provided each have a fixed focal length giving a particular magnification. However, the
highest magnification by no means the most crucial factor when observing. The light gathering power of the
telescope is much more important. You do not only have to use the eyepieces provided, you can select from a
multiplicity of different designs to improve your observing and the quality of your observing. Your telescope's focuser
accepts standard 1.25" size eyepieces. So eyepieces from different manufacturers can be used without
problem. An eyepiece is, in simple terms, nothing more than a magnifying glass which additionally
magnifies the image produced by the telescope. Eyepiece manufacturers do not use just a single lens for this, but
usually a combination of four, five or more lenses. Special designs improve eye relief, extend the field of view
or eliminate unwanted optical aberrations. It is best to use a set of four or five eyepieces which give a range of
magnifications from low to high. A dim and extended deep sky object (DSO) is usually seen much better with a
smaller magnification than with a high one.
In contrast, a planet usually needs a higher magnification.
Determining the magnification
Every eyepiece has a certain focal length. This determines the final magnification at the telescope used.
Long focal lengths give low magnifications, short focal lengths high.
You can calculate the magnification of your eyepieces very simply by dividing the focal length of the telescope
by the focal length of the eyepiece.
Magnification = focal length of the telescope / focal length of the eyepiece
The second figure in the normal designation of a telescope will specify its focal length, e.g. 114/900.
Example: 900mm/25mm = 36X (900mm telescope, 25mm eyepiece)
Tip: Always begin an observation at low magnification and increase it depending upon object.
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