Astronomy Portal to the Heavens, Deep Sky and Universe

Eyepieces

The quality of an image will be no better than the scopes weakest component. Even superior telescopes will produce disappointing views with a poor eyepiece. The good side of this is if you have a reasonable good quality scope putting a good eyepiece in will make all the difference in your viewing pleasure.

You may even find it hard to believe your looking through the same telescope. Most hobbyists carry a set of eyepieces with them, switching out according to the task.

Changing your eyepiece enables you to change these following characteristics of your telescope:

• it's magnification
• it's brightness
• it's field of view

The magnification that an eyepiece will give on a telescope can be expressed as:

Mag=(Telescope f.l.)/(Eyepiece f.l.)

This basically translate like so:

6mm - 9mm high power
12mm -18mm medium power
20mm -32mm low power

While high power gives the obvious reach for close up views it is not the first choice to pop in the scope as many would suspect. The sacrifice is a reduction in brightness and field of view. Low power yields a wide field and brighter objects.

Purchase only 1.25 inch or 2 inch diameter eyepieces. You must see to it that you purchase only scopes that take either or both of these sizes. Scopes fitted with 0.96-inch eyepiece will only leave you frustrated. If you already own one of these eyepieces you should see if it could be changed over to fit the 1.25-inch size. Zoom eyepiece are not recommended.

There are several design types available. Here are the most popular.

Kellner

This three-element eyepiece performs quite well for deep sky work. It is a vast improvement over earlier eyepiece designs. Kellners are low cost and widely available. Kellners cover a 40° field of view and have considerably good color correction. The eye relief is not as good on a Kellner so only the low power ones are comfortable to use.

Orthoscopic

This four-element eyepiece was a favorite for general use for many years. Offers better view then the Kellner with its excellent sharpness and longer eye relief. These eyepieces give a 40° field with the edge of the field being well corrected. Because of it's low cost orthoscopics are a better choice then Kellners.

Plossl

These eyepieces are today's standard of all-purpose use. Their four element design is superior to the ortho's, given excellent contrast and sharpness to the edge of field. Fine image quality on any scope with an apparent field of view around 50. They have excellent eye relief better than an orthoscopic's and are especially good with the demands of short f-ratio reflectors. The popularity of these pieces have kept their prices within reason.

Wide field eyepieces

There's nothing like looking deep into space with a wide field (60°-70°) eyepiece. The views are breath taking pulling the viewer out into the vastness of space. These eyepieces have anywhere from 6 to 8 elements and are difficult to manufacturer. They are wonderful to own but are very expensive. You could spend more money on one of these then you initially invested in a small telescope. It is wise to borrow a few to try on your scope before making such a purchase.

[binoculars] [telescopes] [eyepieces]

 

Related Links

Astromart

Surplus Shack

Orion Telescopes & Binoculars