Eyepieces are essential components to telescopes. Even a telescope of the best optics would be useless without a good set of eyepieces. A telescope’s primary optics gather and focus light while eyepieces magnify that light and bring clarity and detail to the images the telescope produces.
A quality set of eyepieces is an investment that will provide many years of stargazing pleasure. Choosing the best telescope eyepieces is not a decision to make lightly. This guide, supplemented with reviews, will make the selection process effortless. Learn how to use telescope eyepieces, see how they work, and know what to look for when you make your purchase.
Top 3 Best Telescope Eyepieces
Meade Instruments 07199-2 Series 4000 Zoom
Tele Vue 3.7mm Ethos – SX 110°
SVBONY 40mm 1.25 Inch Plossl
Telescope Eyepiece Guide
As with all optics, sizes tell you the bulk of what you need to know about the piece. Such measurements include:
Focal Length and Magnification
In optics, focal length is the distance from the primary mirror or lens to the point where the light is focused. This is the point where an image is formed. Your eyepiece and telescope’s focal length are important because it affects the magnifying power of the eyepiece. Focal length is measured in millimeters. You will find the focal length of the eyepiece written on the actual instrument, and a telescope’s focal length will be included with the manufacturer specifications.
You can determine magnification by simply dividing the telescope’s focal length by the focal length of the eyepiece.
For example, if you have a telescope of 2000 mm focal length with an eyepiece of 25mm you would yield 80 x magnifying power (2000/25 = 80). From these calculations it is easy to see that using the same eyepiece in a telescope of a different focal length will produce different powers, as would using an eyepiece with a different focal length. The smaller the focal length of an eyepiece is, the more magnifying capacity it will have.
Magnification is important to understand so that you get the best out of your selection of eyepieces. A low magnification results in bright, sharp but small images. High magnifications yield bigger images but are dimmer and can become blurry as you push the limits of magnification (although some astronomical bodies, like the Moon, do stand up very well under high magnifications).
The manufacturers of cheap telescopes and eyepieces love pushing high magnification as a selling point, but be very aware of falling into this trap. Higher powers come with a loss of contrast and detail, and if the magnification is excessive the resultant image will be of a very poor quality.
Field of View
Apparent field of view is a measure of how much of a window will ‘fit’ inside your optics (whether talking about cameras, telescopes, binoculars or eyepieces). If you check on your eyepiece, you will see a number written in degrees. Examples for eyepieces include 30°, 50°, or even 80°. An eyepiece that has a narrow field of view will focus on a smaller portion of the sky than an eyepiece with a wide field of view. The apparent field of view can vary from very narrow (25 – 30 °) to very wide (80 ° and upward).
There is an important relationship between field of view and magnification. Magnification affects apparent field of view, resulting in what we call actual or true field of view. To find the true field of view you divide the apparent field of view by magnification. If the eyepiece has an apparent field of view of 50° and you are using 100x magnification, the true field of view would be 0.5°. This covers a section of sky roughly the size of the full Moon viewed from Earth.
Telescope Eyepiece Sizes
One of the things you may overlook when you purchase an eyepiece is the size of the barrel. While the quality and type of views you can expect depend on the eyepiece’s focal length, the size of the barrel describes the diameter of the eyepiece tube. It does not affect focal length. It simply tells you whether or not it will fit into the barrel of your telescope’s focuser based on the telescope’s make.
The majority of telescope eyepieces come in two different barrel diameters: 1.25 inches and 2 inches. The former is by far the more common of the two, even though the 2 inch offers a wider field of view and also provides extra comfort, usually having a longer eye relief.
There is a third type, the rare 0.965 inch eyepieces, but they are quite outdated and it is unlikely that you will purchase a telescope with a barrel of this size.
Eye relief is part of an eyepiece’s optical design. A plain definition of eye relief is the distance your eye needs to be from the eyepiece to be able to comfortably see the entire field of view. Ideally you want a longer eye relief. If the eye relief is too short, you may not be able to get your eyes close enough to get the full field of view. This is problematic because what you will get instead is a blockage of your view called vignetting.
Eye relief becomes even more important when you wear glasses. In this case you cannot do without a long relief; 15 mm at the minimum. Most standard eyepieces are designed in a way that eye relief is proportionate to focal length: a short focal length will mean a short eye relief, and long focal length equals long eye relief. Thankfully modern designs offer a good long eye relief regardless of focal length.
The exit pupil can be thought of as a type of ‘exit aperture’. A telescope’s aperture is the size of the main optic which gathers incoming light. The bigger the aperture, the more light can be collected. This means brighter, clearer and more detailed images are produced. The exit pupil is similar in a way. This is the light leaving the eyepieces to form an image in your eyes. If the diameter of this light is bigger, the images will be better because more of the light is transmitted to your eyes.
To calculate the eyepiece’s exit pupil, get the focal ratio of your telescope. This is the telescope’s focal length in millimetres divided by the telescope’s aperture in millimetres. Now divide the focal length of your eyepiece by the telescope’s focal ratio. Say you have a telescope of 2000 mm focal length and an aperture of 8 inches (203.2 mm). The focal ratio is then f/10. Combined with an eyepiece of 30mm, the exit pupil would be 3mm.
Consider that the human eye has a natural diameter when fully dilated (and your pupils should be fully dark adapted before you start observations). This diameter is different for everyone, but generally it will be around 7mm for children and 5 – 6mm for adults. If the eyepiece’s exit pupil is too small (below 2mm), you won’t get the best image. However, if it is too big, the extra light is scattered and wasted.
Zoom eyepieces are a great way to have an eyepiece with a range of different focal settings all in one. This makes it more convenient than having to swap out eyepieces of varying focal lengths to change the magnification. Most zoom eyepieces will come in focal lengths of 7 – 21 mm or 8 – 24 mm, though there are always more options available if you are willing to shop around and spend a little extra.
Surprisingly, these zoom eyepieces are not very popular in amateur astronomy kits despite the convenience they offer. Part of the issue may be that high magnifications and zooming are usually used in marketing ploys for cheap instruments and accessories. However, this is not the case as top brands all produce quality zoom eyepieces.
That said, there is a downside to using zoom eyepieces. You will have to adjust focus every time you change magnification, and the apparent field of view is narrower. The performance is also not as sharp as single focal length eyepieces, but they are definitely a worthy addition if you are on a tighter budget or just need a more compact accessory.
The Barlow lens is not a true eyepiece, but it certainly deserves a mention in any serious discussion on eyepieces. If you want a cheap, quick and easy way of adding more magnifying power to your set up, the Barlow lens is the answer. You can instantly increase an eyepiece’s power 2, 3 or even 5 fold by using this one handy accessory. The most common type of Barlow lens doubles an eyepiece’s magnification. The really great thing is that a well-chosen Barlow lens does not just double your magnification, but essentially doubles your eyepiece collection!
Like eyepieces, a Barlow lens is sized by its barrel in 1.25 inches or 2 inches (and even the more 0.965 inch) to fit the telescope barrel. The Barlow lens is placed in the telescope barrel before the eyepiece. Once the Barlow lens is positioned on the telescope, you simply insert your eyepiece and focus it. The immediate increase in power does come with a slight loss of detail and clarity when compared to using a separate eyepiece for increased power.
Be careful that you choose eyepieces wisely if you are going to use a Barlow lens, otherwise you can end up with duplicates that have no use. For example, you would not need to purchase a 10mm eyepiece if you have a 20mm used with a Barlow lens. An easy way to know is to exclude any multiples. If you have a 10mm and a Barlow lens, you will not need a 5mm; if you have a 20mm, you will not need a 10mm and so on.
Using Your Telescope Eyepiece
Now that you know what to look for in an eyepiece and how the most important elements come together, we can take a look at using your eyepieces, and how to care for them.
If you are using a Barlow lens, first insert that into your telescope’s barrel before putting the eyepiece into the Barlow lens. If you are not using a Barlow lens, skip this part and put the eyepiece directly into the telescope’s barrel. You will then get the eyepiece in focus by adjusting the knobs on the side of or below the eyepiece. Do not put your eye directly on the eyepiece – this will cause a black ring to form around the outer edges, obscuring your field of view. This is one of the reasons you need good eye relief. Continue to adjust until the image is sharp, clear and overall pleasing to look at it.
You do not have to stick to only one eyepiece, even if you will be observing the same object throughout the night. In actual fact, you will want to play around with different focal lengths so that you can get the best choice for each individual object. Start with the lowest magnification and slowly up the power until you are happy that you are using the best focal length for a particular object.
Here is a brief overview of which focal lengths work for viewing various celestial bodies:
- Under 7mm: Very short focal lengths yield a high magnification. They work most effectively with refractor telescopes with a long focal length. You need incredibly good seeing (steady atmospheric conditions) to be able to get the right results from short focal length eyepieces. That is because the sensitive power will pick up on every bit of atmospheric interference and magnify it. An eyepiece of around 5 or 6mm is a great choice for separating binary stars and excellent for Solar System viewings, but only under good atmospheric conditions.
- 7 – 13mm: This range is compatible with telescopes of short focal lengths, and perfect for viewing within the Solar System.
- 14 – 18mm: Great midrange focal lengths that are versatile whether for lunar observations, planetary viewing, or exploring deep sky objects.
- 19 – 24mm: A great choice for viewing open clusters and nebulae.
- 25 – 39mm: Good for observations on objects that cover a very wide field of view.
- 40mm and upward: These very long focal length eyepieces are best used with telescopes that have very short focal lengths.
How Many Telescope Eyepieces Do I Really Need?
As your hobby in amateur astronomy grows, so will the number of accessories – including eyepieces. The ultimate goal is to have a range of eyepieces of varying focal lengths. It adds to your observations because you will always be able to view an assortment of different celestial bodies at their very best. An open star cluster such as the Pleiades is beautiful to explore under low magnification and a wide field of view. On the other hand, the Moon and planets show remarkable detail when viewed with higher powers, and the field of view can be much narrower without diminishing the experience. To add to this, having a number of eyepieces within the same range of focal lengths is useful. Small increments can make a significant impact on the clarity of your images.
Even as a novice backyard astronomer you will want at least three eyepieces and a Barlow lens. Go for a shorter focal length, a midrange piece, and a piece with a longer focal length so that you can have a practical range of magnification and field of view (do not immediately go for the very lowest or highest focal lengths).
Maintaining Your Eyepieces
The finest quality eyepieces still could not produce crisp images if they are dirty, scratched, or damaged in any other way. Despite the importance of caring for your eyepieces, most of them do not come with cleaning instructions upon purchase. It is a rather straightforward process, and you only require a few basic tools: a microfiber cloth, cleaning solution which consists of only pure alcohol and water, and some Q-Tips. Also have a well-lit place where you can work.
Note: be careful as you clean the eyepieces, as you do not want to scratch the coating on the piece.
Lightly brush away any dust using the microfiber cloth. Sometimes this is all the cleaning the eyepiece needs. If there are any greasy smears, lightly dip the Q-Tip into the cleaning solution, taking care that it does not become saturated with alcohol. You do not want the cleaning solution to pool on your eyepiece. Start from the center of the eyepiece, gently working your way toward the edges in circular motions. Rub any excessive away with the microfiber cloth.
Store your eyepieces in their proper casing, and always handle your accessories with care. A quality eyepiece can last for many years.
Best Telescope Eyepiece Reviews
Here is a look at some available eyepieces for you to consider as you build your collection:
Meade Series 4000 Zoom Eyepiece, 1.25 Inch
A zoom eyepiece can be a good choice for beginner hobbyist, especially if you are still trying to figure out focal lengths, magnifications and field of view. It is certainly not the only eyepiece you should have, but nevertheless the Meade Series zoom eyepiece is very convenient.
It offers you a range of five different magnifications. Simply rotate the eyepiece band to change focal length from 8, 12, 16, 20 and 24mm. The piece works well for resolving binary stars, and for deep sky observations.
Tele Vue 3.7mm Ethos – SX 110° Eyepiece
Though this piece is expensive, it does not disappoint as a worthwhile investment. The short focal length paired with its exceptional field of view make is a fine choice for advanced Solar System observations and deep sky explorations. It is an excellent quality make, with very high light transmissions delivering sterling images.
SVBONY 40mm 1.25 Inch Plossl Eyepiece
Opt for SVBONY 40mm Plossl piece for unbeatable monetary value: it is very well priced for such a versatile and sturdy piece. The eyepiece has a 40° apparent field of view which some may find a little modest, but which is a good medium for observing several night sky objects.
Explore Scientific 82° 4.7mm Eyepiece
There are some nights when even a slight change in weather can dampen your observations, and having a water resistant eyepiece can be a total game changer in such an environment. The Explore Scientific 82° delivers stunning images with an exceptional field of view. The magnification, though moderate, also produces detailed images. The design is solid and stands up to bigger brand names.
Celestron 93325 40mm Omni Eyepiece
If you wear glasses, the 40mm Omni from Celestron is a dream. The rubber eyecups are not only comfortable but fold down to accommodate for spectacles. The eyepiece has a field of view of 45° and produces wonderful images, though there can be some slight blurry toward the edge of the field of view. Not too bad considering how affordable the eyepiece is and from such a reputable name.
Orion 8725 32mm Sirius Plossl Eyepiece
Expect high contrast, detail and brightness from Orion’s 32mm Sirius Plossl. Some may consider the 52° field of view too narrow, but you can still sweep a number of beautiful objects with this quality eyepiece. The eye relief is long, the build is strong, and the optics are multi coated to deliver the best images.
Meade Instruments Ultra Wide Angle 20mm 2 Inch Eyepiece
An eyepiece like the Meade Ultra Wide Angle 20mm is an absolute necessity if your telescope is designed for the less common 2 inch barrels. It is also does not disappoint if deep sky observations is where your passion lies. The large field of view brings nebulae, clusters, and an assortment of other deep sky objects to life. You can even bring observations back home and explore the entire Jovian system with the wide angle view. The piece has good eye relief, though the eyecups themselves may not be the most comfortable design.
Orion 08711 Shorty 1.25 Inch 2x Barlow lens
The Orion 2x Shorty Barlow lens is a classic and reliable addition to any eyepiece set. It will instantly double the power of any eyepiece, and still retain the quality of your images. This Barlow lens has great light transmission so images remain bright. The lens is multi coated, compact, and threaded for all 1.25 inch eyepieces. A definite must when you need to add extra magnifying power on a budget.