Using a telescope is the best way to view astronomical events as well as remote objects. It has been one of the oldest educational products in the world which is still being used today. There has been a lot of changes and developments for telescopes but what didn’t change is their ability to let us view the sky clearly, and in fact, it became even better.
There are many kinds of telescope to choose from, however, the quality of its view does not depend only on its brand or model but on an important part as well, which is the eyepiece. Maybe you’ve had your telescope for quite some time now, but have you ever tried buying different eyepieces for it? If you haven’t, it means that you’re still using the budget models of eyepieces that came with your telescope.
Eyepieces are one of the most important accessories for telescopes because they define the magnifying power at which you’re viewing. They are responsible in bringing the object closer, as well as in widening the field of view to be able to observe a larger area of the sky. And just like the telescope models, eyepieces also come in a wide variety of sizes and designs.
Adding the correct eyepiece to your telescope is important because it can drastically improve your astronomy experience. This means that if you have different kinds of eyepieces, you will be able to turn a high quality telescope into a more powerful tool.
For you to choose the best eyepieces for your telescope, you need to understand first some important things about it such as its magnification, its range of sizes, and its field of view.
Telescopes have focal lengths which is the distance from the main lens to the point at which it forms an image of an item from afar. You can usually see this figure printed near the eyepiece focuser. It is the clearest marker of how powerful your telescope is. A telescope’s focal length commonly lies in the range of 400 to 300 mm, depending on the aperture as well as the type of telescope. But aside from your telescope, its eyepieces have focal lengths as well which range from 25 to 10 mm.
For you to calculate the magnification or power, you just need to divide the focal length of the scope by the focal length of the eyepiece. For example, a scope with a 2000mm focal length when used with a 25mm eyepiece, will have a power of 80 or 80x.
However, you have to remember that there’s also a limit when it comes to magnification. This is to avoid wasting light from the telescope eyepiece to spill around the dilated pupil of the eye. To know the largest-focal-length eyepiece you can use with your telescope, what you need to do is multiply the focal ratio by 7. The focal ratio is the focal length of your scope divided by its aperture. For example, if your scope is f/5, the largest-focal-length eyepiece that you can use is 35mm.
Sizes of Telescope Eyepieces
The physical sizes of telescope eyepieces are very important if you’re considering to purchase or use an alternative eyepiece for your telescope. The common telescope eyepiece size that is widely available today are those which have chromed barrels with a diameter of 1.25 inches or 31.7 mm. It is usually slid in the push-fit focusers of most telescope models. There are also eyepieces which barrels are 2 inches or 50.8mm in diameter. Older scopes on the other hand are those that accommodate 0.965 inch or 24.5mm barrels.
You can use any brand of eyepiece in your telescope as long as its barrel size matches the barrel size of the focuser of your telescope. Astronomical telescopes usually use 1.25 inch eyepieces, but they can also sometimes take 2-inch eyepieces.
The reason why there is a 2-inch size of eyepiece is because you cannot fit a combination of long focal lengths or low magnification, and wide fields of view in a 1.25-inch barrel because it will be too narrow. You will only need it if you’re exploring for low magnification eyepieces with wide fields of view. But before purchasing a 2-inch size of eyepiece, make sure it can fit your telescope.
Field of View
The field of view of a telescope eyepiece will tell you the width of sky, in angular terms, that is presented to your eye, and it is measured in degrees. Eyepieces that have larger apparent fields will be able to let you see a greater view of the sky compared to those smaller ones. Eyepieces with simpler designs usually have apparent fields of about 45 degrees. Wide-field designed ones on the other hand, are usually 60 degrees or more.
The true field of view is another important thing you should know about eyepieces. You can obtain this by dividing the apparent field by the magnification the eyepiece delivers. For example, a 10mm-focal-length eyepiece that has 50 degrees’ apparent field is used on a scope with 1,000mm focal length. Its magnification will be 100x, and the true field will be 50°/100x or 0.5 degrees.
How Many Telescope Eyepieces Are Needed?
If you want to cover a wide variety of object, you will probably need several eyepieces. It’s because with telescopes, magnification is changed through changing eyepieces. If you will be viewing the moon and some planets, you need an eye piece with a high magnification. To view brighter deep sky objects such as star clusters and galaxies, you need an eyepiece with medium magnification. To view faint deep-sky objects or very large objects, a low magnification eyepiece is needed. Therefore, you can have a minimum of three eyepieces to be able to view all of these things.
Types of Telescope Eyepieces
There are many types of telescope eyepieces available in stores today. They have different designs and characteristics and here are some of them.
- Orthoscopic Eyepieces: This type of telescope eyepiece is for the optically fast Newtonians. It has a four-element design, meaning, it has four lenses inside.
- Plössl: This type of eyepiece is good to use for all kinds of telescope because it can deliver well-corrected, wide fields of view with good eye relief. You can position your eye behind its rear lens at a comfortable distance and you can still see the whole field of view. It is perfect for those who wear glasses.
- Lanthanum and Ultra-Wide: These eyepieces are for high-power lunar and planetary viewing. They usually have six to eight-element designs which combine wide apparent fields and comfortable eye relief across the focal-length range. Some of them even feature exotic rare-earth glass elements that help reduce optical aberrations. However, these types of lenses are usually very expensive.
Barlow lenses are not telescope eyepieces but it is a useful device. It is inserted into the telescope’s focuser before the eyepiece, and it can double or even triple the magnification. Barlow lenses can help you double your eyepiece investment by making each of them perform at two powers. If you only have a minimum of three pieces of eyepieces, this will be very useful for you.
Now that you know the basics about telescope eyepieces, you can now choose the best ones that will work for your telescope. To help you out, here are some telescope eyepieces we can recommend.
This is a 1.25-inch eyepiece with a 33mm high-magnification which is designed for planetary and lunar viewing. It features a flat design and has a 55-degree wide apparent field of view. It also has a long 20mm eye relief if you’re viewing with your eyeglasses on.
This eyepiece has a 4-element plossl design which is perfect for viewing medium-sized star clusters and a wide range of cloudy nebulas. It is a 1.25-inch 10mm eyepiece that will give you a wide viewing field, extra sharpness, and long eye relief.
This is a super-premium eyepiece that has a focal length of 8 to 24 mm. It also has a 40 to 60 degrees’ field of view and 15 to 18mm eye relief. It also features fully multicoated optics.
This 1.25-inch with 8 to 24mm focal length eyepiece will give you the widest viewing field together with extra sharpness and long eye relief. It also folds down, making it convenient for eyeglass wearers.
This eyepiece has a 40mm focal length with a 4-element premium symmetrical Plossl optical design. The lens edges are blackened to minimize internal reflection while maximizing contrast at the same time.
This eyepiece is made with high quality 4-element design. It offers 40 degrees’ apparent field of view which is perfect to use for broad field lunar observations. It is fully coated with black interior design. It has a 1.25-inch size that will fit any 1.25-inch diameter telescope.
If you want to turn up the magnifying power of your beginner telescope, then this is the best and affordable eyepiece for you. It features 3.66mm focal length that will boost the power of your telescope. It has a size of 1.25 inches and has fully coated glass optics.
This kit contains five superior grade Plossl eyepieces. All of them are fully-multicoated for maximum contrast and resolution. Aside from that, it also includes two 1.25-inch Barlow lens that will give you a total of ten power combinations. It also has six colored eyepiece filters for planetary viewing. You will be able to save more compared to buying these in individual pieces.
This waterproof telescope eyepiece has a 62 degrees’ field of view as well as a near par focal design that will transform your visual astronomy experience. Its design will allow you to see fainter images.
This is a high-quality two-inch 38mm super-wide angle telescope eyepiece. It has 70 degrees’ field of view that will give you an amazing view of the sky. It features five multi-coated lens elements that are made with high index glass which deliver sharp and high contrast vistas. It is a beautifully made telescope eyepiece that offers a great performance.
Using different telescope eyepieces will definitely make you enjoy observing the skies more. We hope the information and products we shared will help you find the best eyepieces for your telescope.