Choosing the right telescope eyepiece is crucial to fully realizing the potential of your telescope. While the telescope itself gathers and focuses light, it’s the eyepiece that determines the magnification, field of view, and image quality of what you see. Just as a camera lens shapes the photograph, a good eyepiece shapes the view of the stars, planets, and galaxies. With a wide variety of eyepieces available, understanding the key attributes can help you make an informed choice and elevate your stargazing experience.
When selecting a telescope eyepiece, consider the following attributes:
Focal Length
The focal length of an eyepiece, typically measured in millimeters (mm), determines the magnification it provides when paired with a particular telescope. Shorter focal lengths offer higher magnification, making them ideal for viewing planets and the moon in detail, while longer focal lengths provide a wider view suitable for deep-sky objects.
Apparent Field of View (AFOV)
The apparent field of view is the angular measurement of the eyepiece’s visible field and influences how expansive the view feels. Wider fields of view, such as those provided by 68° or 82° eyepieces, offer immersive visuals and are particularly beneficial for locating and observing large celestial objects like star clusters.
Eye Relief
Eye relief is the distance between the eyepiece lens and your eye where the entire field of view is visible. Eyepieces with long eye relief (usually 15mm or more) are more comfortable for extended observing sessions, especially for eyeglass wearers.
Barrel Size
The barrel size of an eyepiece, typically 1.25” or 2”, dictates its compatibility with your telescope. Larger 2” eyepieces allow for wider fields of view but require a telescope with a 2” focuser.
Lens Elements and Coatings
Quality lens elements and anti-reflective coatings can minimize optical aberrations and maximize light transmission, resulting in sharper and brighter images. Premium eyepieces with multi-coated optics will often yield crisper views, making them worth considering for serious observers.
Design Type
There are various eyepiece designs, including Plössl, Orthoscopic, and Nagler, each offering different benefits in terms of image quality, comfort, and affordability. Understanding these designs can help narrow down the best choice for your observing needs.
Selecting the right combination of these attributes can transform your stargazing experience from average to extraordinary. In this article, we will explore these characteristics in more detail, provide recommendations for different types of observations, and guide you in building a well-rounded eyepiece collection that complements your telescope setup.
Huyghens Telescope Eyepieces
Huygens eyepieces are a classic type of optical design primarily used in telescopes and microscopes. Developed by Christiaan Huygens in the 17th century, they consist of two plano-convex lenses separated by a small air gap. The design is simple and effective for low to medium magnifications. Huygens eyepieces are characterized by having a narrow field of view (approximately 30° to 40°) and are best suited for long focal length instruments. Although they produce some chromatic and spherical aberrations, they are still widely used in entry-level telescopes due to their affordability and historical significance in optical design.
Kellner Telescope Eyepieces
About 150 years later in 1849 Carl Kellner created the first achromatic eyepiece using special glasses. This was a vast improve reducing aberrations and also had good color correction. The only problem was this eyepiece had internal reflections. Today modern coatings are applied to eliminate reflections making this a fair inexpensive eyepiece.
Orthoscopic Telescope Eyepieces
(A planetary eyepiece)
The next innovation came about 30 years later in 1880 by Ernst Abbe. With good color correction, minimal spherical aberration, good contrast, and a flat field of view these have been one of the most popular eyepieces for more than 100 years. With newer wider field eyepieces developed in recent years this eyepiece is not quite as popular. Since contrast and color are more important than field of view when viewing planets, this is still a popular planetary eyepiece. This is one of my favorite eyepieces for viewing planets.
Plossl Telescope Eyepieces
(A versatile eyepiece)
Developed in 1860 by an Austrian optician named G.S. Plossl, it was nearly 100 years before this eyepiece became popular. These are expensive to make and therefore cost more than an ortho. These eyepieces have great eye relief, field of view, and contrast making them a ideal for all observing targets. more...
Erfle Telescope Eyepieces
Erfle eyepieces are a type of wide-angle eyepiece design originally developed by Heinrich Erfle in the early 20th century. They are known for their relatively large field of view, typically ranging from 55 to 65 degrees, making them ideal for deep-sky observations and wide-field astronomical viewing. Erfle eyepieces feature a 5- or 6-element configuration that includes at least one achromatic doublet, providing a balance between image quality and field of view.
Although Erfle eyepieces offer excellent clarity and contrast in the center of the field, they tend to show edge distortion and chromatic aberration at the periphery, especially when used in telescopes with shorter focal ratios. Due to these limitations, they are more commonly used in longer focal length telescopes, where the aberrations are minimized.
Today, Erfle designs have largely been supplanted by more modern eyepiece technologies such as the Nagler and Ethos lines, which provide wider fields of view and better edge correction. However, Erfle eyepieces are still valued by amateur astronomers for their affordability and performance in less demanding observing scenarios. more...
Super Wide Telescope Eyepieces
These modern eyepieces have a field of view from 65-70 degrees. With the creation of the Televue Panoptic by Al Nagler a revolution in eyepiece design was spawned. The competition is fierce which is great for eyepiece consumers. These eyepieces are great for viewing large nebulae and star clusters. more...
Ultra-Wide Telescope Eyepieces
With field of view of 80 degrees and greater, these eyepieces have become very popular with astronomers will to lay out the big sums of money. While these are great for many objects, a simpler design may give a better view of small bright objects like planets. more...
Barlow Lenses for Telescopes
While not actually an eyepiece, a barlow is attached to an eyepiece that magnifies the image. Barlows are purchased by magnification power (1.5x, 2x, 4x...) Barlows are mainly used for planetary or binary star viewing since they can reduce the amount of light passing through. They are also a way to get high magnification and good eye relief at the same time. more...
Zoom Telescope Eyepieces
Zoom eyepieces are very handy since as their name implies the magnification factor can be adjusted. While this makes them useful, a good quality zoom is very expensive and still not as good as having several eyepieces of varying magnification. more...
Bino Viewer Telescope Eyepieces
Bino viewers are devices that allow you to use both of your eyes to view the image in a telescope. The results are truly dramatic. Images have an almost 3-dimensional look. When you use both eyes you are also using both sides of you brain.
The thing to keep in mind about Bino viewers is that you need two of each eyepiece. This can become very expensive. more...