Telescope eyepieces determine both magnification and field of view for visual observing. In most cases an eyepiece contains more optical elements than the telescope itself. A carefully chosen eyepiece set will help to maximize the enjoyment of your telescope. Quality eyepieces will maximize telescope performance by allowing it to reach its full potetial. While most eyepieces will perform well in the slower f/10 focal ratio of a Schmidt-Cassegrains, many will not perform well with f/6 faster optics common to Newtonian reflectors and today's apochromatic refractors.
The table below displays popular brand eyepieces from TeleVue, Explore Scientific, Orion and several others. This is a long page, so please be sure to scroll all the way to the bottom.
Telescope Eyepieces for Astronomy
A telescope collects light and converges those light rays to a focal point. The eyepiece takes over from there, forming the image you see. The eyepiece also determines both the magnification and the true field of view that you see, which is why different eyepieces are needed to observe different objects. Eyepieces have a far greater impact on your observing experience than any other telescope accessory.
Eyepieces are complex devices, usually containing more optical elements than the telescope itself. A carefully chosen eyepiece set will help to maximize the enjoyment of your telescope, but you must carefully choose them based upon the types of objects you plan to observe. Four major factors to consider include:
- Magnification: Eyepieces determine the magnification at which you view a celestial object. While most people think the higher the magnification the better, this isn’t always true. For example, high magnification might be a good choice for viewing an individual planet, but would be a poor choice if you wanted to see an entire nebula. Since the field of view decreases with magnification, the higher your magnification, the less of the night sky you can see in a single view.
- Field of View: Magnification and field of view are largely linked — the higher the magnification, the smaller the field of view. Some eyepieces offer larger fields of view at the same magnification, allowing a larger object to be seen within the field. Field of view is important to consider when viewing larger objects, like the Orion Nebula or the Andromeda galaxy.
- Exit Pupil: This is perhaps the least understood yet most important consideration when choosing eyepieces. Exit pupil is the diameter of the light cone leaving the eyepiece at the point where the image is formed. It is calculated by dividing the eyepiece focal length by the telescope focal ratio. The human eye can accommodate up to a 7 mm exit pupil; anything larger is a waste. There are also practical considerations on the lower end of the exit pupil spectrum. In simple terms, an exit pupil of 2 mm or larger tends to be best for viewing deep space objects, whereas an exit pupil of 0.5 to 1 mm is generally best for observing the planets.
So how do you determine the magnification of an eyepiece? The focal length of the eyepiece is the most important number — this is given in millimeters on the side of every eyepiece. Simply divide the focal length of your telescope by the focal length of your eyepiece to determine the magnification you’ll achieve. The lower the number on your eyepiece, the higher the magnification you’ll get overall.
Where to Buy Telescope Eyepieces
At Skies Unlimited, we offer quality eyepieces for telescopes from several brands, including TeleVue, Celestron, Explore Scientific, Orion and others. The list is long, so please be sure to scroll through the entire page to see the full stock of telescope eyepieces for sale.
We also offer advice on how to select the best telescope eyepieces for your application and how to use them properly. Call Skies Unlimited today or visit us at our Pottstown, Pa., location to speak with a staff member and determine the best eyepiece choices for your celestial viewing experience. Visit Skies Unlimited to buy telescope eyepieces today!