Telescope either uses a lens or a mirror for gathering and focusing
light. Reflector telescopes
use mirror while refracting telescopes use lenses instead of mirrors.
Both have their own advantages.
As mentioned above, lenses are used in refractor telescopes. They are used to bend the light coming from the far distant objects. This bending of light enables you to see that distant object. A refracting telescope uses two lenses. One of these lenses is usually bigger than the other one.
Eye-piece uses lens in many telescopes. There are also some types of telescopes that have no lens in the eye-piece. However, eye-piece still remains the most important part of a telescope since you will see the sky through this eye-piece.
The eye-pieces usually are adjustable and are low powered. You can use the eye-piece in order to adjust the magnification of the telescope. The type of eye-piece for your own telescope depends on your personal choice. There are many different eye-pieces available today. Amongst these varieties, it sometimes becomes difficult to choose the right one.
For this reason, you should have evaluation criteria for these eye-pieces.
You can evaluate an eye-piece through various characteristics like the
size of the field, sharpness that it provides, optical quality, its brightness,
price (varies from person to person), effects to your eyes, barrel size
Huygens and Ramsden are the name of the lens designs that were used in older versions of telescopes. These are not recommended for professional astronomers because they don’t provide good quality.
Although they are quite cheaper but they don’t provide good quality. They also can’t help you against various aberrations like chromatic aberrations and light circles around various brighter objects like stars in the night sky.
Orthoscopic designed lens is ideal for both professional astronomers and other novice sky gazers. This design provides a 45 degree FOV (Field of View) which is quite narrowed and it uses 4 lenses for the eye-piece. Remember, eye-piece is the most important part of any telescope.
The main advantage of using this design over other designs is that it gives the user a sharp view without having eye strains and is recommended for viewing planets as well.
If you budget is neither too high nor too low then you should go for a Barlow lens. This sort of design will give you an average quality but still value for money. It is neither too expensive nor too cheap that could give you poor quality.
These lenses are available at price ranging from $30 to $70. They provide an average magnification which is mostly suitable for non-professional people. It is also recommended for those who have adopted astronomy as a hobby- not as a profession.
One of the most advisable tips is to look for a lens for your telescope
that is adjustable in order to suit your need. If you lens is adjustable,
it means that you can view stars as well as planets by adjusting your
lens making it value for money.