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Choosing Eyepieces

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Eyepieces are necessary to CHANGE the MAGNIFICATION of your telescope, so you need 3 or more.

Some people new to amateur astronomy refer to eyepieces as LENSES, however they are called EYEPIECES.

2

Looking through an Eyepiece

a

POSITIONING  To get the best view through an eyepiece, you have to center your eye over the top lens and position it above the top lens at the “correct” distance. In the dark, this “spot” can be a little challenging to find. This is different for every eyepiece, so you have to reposition your eye for every eyepiece.

FOCUSING  If everyone had 20/20 vision, the image through an eyepiece would always be perfectly focused. Unfortunately, this is not the case, so almost always, the “telescope” will need to be refocused for you to achieve a sharp image. When properly focused for your eyes, stars should always appear as pinpoints.

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Summary and Recommendation

Choosing eyepieces is very confusing because there are many types and almost every telescope manufacturer or major astronomy-type business has their own line(s) of eyepieces.​ Additionally, there is a incredible range of prices but you can get decent optical quality for a reasonable price.

For a starting set of eyepieces , my current recommendation is the SVBony 4-piece eyepiece set (available on Amazon—can buy individually) as shown to the right which has a good balance between cost and performance, and these will also work for eyeglass wearers.

I have two sets of these that I use for the general public when they look through my telescopes—they are probably the best value around. And, NO, I do not get any type of compensation for this recommendation. This is my own recommendation based on experience with these eyepieces.

CLICK on the IMAGE of the eyepieces to take you to the Amazon page to read more and purchase these eyepieces.

Set of four SVBony Ultra Wide Angle Eyepieces
1. Priced at around $130 for all four. Sometimes they go on sale. They are only available through Amazon.com. Make sure you get the eyepieces as pictured. SVBony sells less expensive eyepieces that I DO NOT recommend.
2. The set has focal lengths of 6mm, 9mm, 15mm and 20mm which will provide a nice range of magnifications.
3. Their eye relief is 17mm for all four eyepieces which provides a comfortable viewing distance to place your eye over the top of the eyepiece. This works for individuals with or without eyeglasses.
4. These eyepieces have a nice wide "field-of-view" which means that the circle or “window” forming the image is big enough where you don't feel like you are looking down a tube.
5. Mechanically, these eyepieces are made well.​ Now, the bottom red rings are screwed on and can come loose, so turn it to tighten it—check this on receipt and every now and then.

Calculating Magnification

MAGNIFICATION = Telescope Focal Length ÷ Eyepiece Focal Length
All lengths must be in millimeters!

Magnification 
Calculation Example

1. You need to know the focal length of your telescope in millimeters (mm). Often this is indicated somewhere on your scope, otherwise consult the internet.

2. Divide your telescope focal length by your eyepiece focal length to calculate magnification.

3. For the eyepieces shown to the left, if you had a telescope with a focal length of 540mm, then your magnifications would be:

You need to change eyepieces to change the magnification of your telescope. ALL eyepieces have a number noted on their barrel indicating their focal length in millimeters. (Sometimes other information is also noted.)

Eyepiece focal length varies from about 3mm to 55mm. Most amateurs starting out should try to acquire a set of 3 or 4 eyepieces. A possible set might include a 6mm, 10mm, 18mm and 25mm.

NOTE:  The shorter the focal length (smaller mm number), the higher the telescope magnification.

540mm ÷ 25mm = 22x
540mm ÷ 18mm = 30x
540mm ÷ 10mm = 54x
540mm ÷ 6mm = 90x

How do you get HIGHER magnifications if this were your set of eyepieces?
By using a Barlow lens in conjunction with your eyepiece to double the magnification—see discussion farther below.

Magnification Recommendations
Planets and Moon:  50x to 300x (see Note)
Galaxies, Nebulae and Cluster of Stars:  50x to 150x

NOTE
Observing the Moon & Planets
It is not always possible to observe the Moon and Planets with more than 100x because the atmosphere is often turbulent which causes images greater than 100x to be very blurry. On those good nights when the “seeing” is very steady, push your magnification as high as you can to get great views of the Moon or Planets. Oh, observing the Moon and Planets when they are 30° or less to the horizon is always poor because you are looking through more atmosphere and thus they will always appear blurry.

Eyepiece “Window”  •  Apparent Field-of-View (AFOV)

It is the difference viewing celestial objects by looking through a ship’s porthole or a picture window.

One of the biggest difference in eyepieces and thus price is the size of the "window" that you get to look through. An extreme example would be the difference between looking through a porthole on a ship and a picture window in your home. The least ​expensive eyepieces are like looking through a “small” porthole and the most expensive eyepieces are like looking through a “large” picture window.

Window Sizes
The size of the window that an eyepiece provides is called Apparent Field-of-View (AFOV). This varies from about 50° to 110° (see images). All Plössl eyepieces (the basic eyepiece) provide a 50° AFOV, which is about the smallest AFOV for today’s eyepieces (and it is an adequate AFOV), however, there are some very cheap eyepieces that are less. 

Prices
The price of eyepieces go up and it can be a lot as the AFOV increases from 50° to 100°.
A 50° Plössl can cost as little as $20 while a 110° Ethos (a brand name) from the company Tele Vue can cost $750+!

Overall a 60° AFOV is more than adequate and satisfying for all visual observing. And, you can purchase eyepieces like this for under $100 each and that also have a generous eye relief (see topic farther below).

Taking Full Advantage
When an eyepiece’s AFOV gets around 60° or more, you will actually have to move your eye to “look around” to see the edge of the eyepiece’s view. And, two factors that can hinder experiencing the full AFOV is short Eye Relief (see article farther below) and the soft Rubber Eye Guard. 

How to Determine/Find the AFOV of an Eyepiece or Eyepiece Set
Sometimes the AFOV is noted on the eyepiece barrel, however, often it is not. So, the only way to determine the AFOV is to look up the specifications of the eyepiece on the internet. Usually the site from whom you purchased the eyepiece has the information, otherwise the manufacturer’s site (like Celestron or Explore Scientific) will have it listed. I have never received an information/specification sheet with any eyepiece that I have purchased and even the expensive ones!

Window Size
AFOV (Apparent Field-of-View) is the size of the eyepiece window you look through when viewing celestial objects. 50° is the smallest "window."

Orion Nebula
This is an image of the Orion Nebula—you won't see colors like this through the eyepiece. The blue nebula below the Orion Nebula is difficult to see visually​ but the associated stars are easy to see.

The largest AFOV, so far, is 110°. There is no real need to go beyond 82°.

Plössl Eyepieces

The Plössl eyepiece is NOT a brand or the name of a company. 
It is the name of an optical design for an eyepiece that has been around since 1860. 
Not too long ago, it was a premium type eyepiece. Today, it is a basic, low-cost and starter type eyepiece.

Overall, the focal lengths of 6mm to 15mm are NOT recommended for eyeglass wearers because of the short eye relief.

1. The optical performance of Plössl eyepieces is excellent.
2. The main problem with the Plössl is that the eye relief is very short for the shorter focal lengths of 6mm to 15mm which provide the medium to higher magnifications. This means that you have to literally shove your eye up against the top of these eyepieces to see anything—it is very uncomfortable.
3. The Plössl design provides a 50° AFOV (Apparent Field-of-View) which is very adequate for visual observing but is on the smaller side compared to more modern eyepieces having 60° AFOVs or more (see article above).

Plössl  
Focal Length eyepieces to AVOID:
6mm to 15mm. See #2 to the right.

The Plössl to the immediate right has a 2-inch barrel diameter. It’s focal length is 55mm, which is about the longest focal length available.

A family of Tele Vue Plössl eyepieces that I purchased a long time ago but seldom use anymore. 
From left to right: 55mm, 40mm, 32mm, 25mm, 20mm, 15mm, 11mm, 8mm.  

Eye Relief

Eye relief is the distance you have to place your eye above the eyepiece to “properly/fully” see the image. For some eyepieces, this is too close and uncomfortable.

1. For those who must wear eyeglasses to observe, the eyepiece should have a eye relief of about 15 millimeters or greater.
2. Ideally, if you can observe without your eyeglasses, do so. Try it if you are not sure.
3. If you don’t need eyeglasses for observing, get eyepieces having eye relief of at least 10 millimeters.

The eye relief distance can vary from about 5mm to 20mm, or more.

Eyeglasses.  If you must wear eyeglasses to look through an eyepiece, you need a eye relief of about 15mm to 20mm or more (38mm is about the max). 20mm or so is probably ideal.

Comfort.  An eyepiece having around 20mm of eye relief is very comfortable for viewing with or without eyeglasses. If you don’t need eyeglasses to observe, almost anything below 10mm is too short because you have to shove your eye too close to the top of the eyepiece—this is uncomfortable and your eyelashes might get in the way, too.

Eyepiece Families.  There are families of eyepieces that are designed with the same eye relief for each eyepiece in the set—usually around 20mm to accomodate eyeglass wearer (but also great for those who don’t need them). You can always buy individual eyepieces in a family/set.

Rubber eye guards at the top of the eyepiece are necessary for eyeglass wearers because you won’t scratch your eyeglass lens. In general, for all observers, the rubber eye guards make it more comfortable (softer and warmer) to look through eyepieces. 

1.25-inch & 2-inch Barrel Diameter

The standard eyepiece barrel diameters are 1.25 and 2 inches. This is a worldwide standard!
You ONLY need to purchase 1.25-inch barrel diameter eyepieces.
You will never be disappointed using “just” the 1.25-inch barrel diameter eyepieces.
I have a few 2-inch diameter barrel eyepieces and I very rarely use them! 

WORLDWIDE STANDARD
It is ironic that all measurements of astronomical telescopes and equipment are metric, mostly in millimeters. BUT, the dimension of eyepieces is in inches! The US “won” this battle. Worldwide, the barrel diameter of eyepieces is 1.25 and 2 inches.

WHY 2-INCHES?
The only reason that there are 2-inch diameter eyepieces is because for some eyepiece focal lengths (mostly the longer focal lengths), they can provide a greater AFOV (Apparent-Field-of-View) than is possible with the 1.25 inch eyepieces. Remember, AFOV is the size of the window you get looking through an eyepiece. 
The only way to achieve a 100° to 110° AFOV, that is, the size of the window that you get to look though an eyepiece, is with a 2-inch barrel diameter.

It is sort of a guy thing to want a big 
2-inch barrel diameter eyepiece. But, I am telling you, they provide very little advantage over any 1.25-inch eyepiece. And, the cost of 2-inch eyepieces can be astronomical—anywhere from $300 or $400 each to over $800 each.

There is NO difference between the optical quality of 1.25 and 2 inch eyepieces.
The only difference is that a 2-inch eyepiece can provide a greater AFOV, a greater field of view, that is, a larger window to look through that is not possible with the 1.25 inch barrel. But, you can get large AFOVs for 1.25 inch eyepieces that are large enough for anyone’s need.

Best use of 2-inch Eyepieces
Probably the best and only real use for 
2-inch eyepieces is on larger telescopes with longer focal lengths. For example, I sometimes help the public look through a 40-inch diameter telescope with a focal length of 148 inches (3,759 millimeters). I usually insert a 2-inch eyepiece of 21mm focal length with an AFOV of 100° (An Ethos eyepiece made by Tele Vue). This provides a magnification of 179x and a true field of view of a little over 0.5° which is the diameter of the Moon.

The Barlow

A Barlow let’s you double (or more) the magnification of any eyepiece—all the ones you own.
A barlow DOES NOT change any optical characteristics of an eyepiece.

Barlows are often necessary to achieve the higher magnifications. 
For shorter focal length telescopes, especially refractors, using a barlow will be the only means to increase and achieve the higher magnifications (150x to 300x) needed for observing the Moon and Planets. 

For example, about the lowest eyepiece focal length is 3mm, (remember, the smaller the eyepiece focal length, the higher the telescope magnification). If your telescope has a focal length of 400mm, a 3mm eyepiece yields a magnification of 133x (400÷3). To go higher than this, you will need to use a barlow.

Eyepieces are inserted into a Barlow, an eyepiece-size optical tube, which is then inserted into the eyepiece holder. A barlow will double (or more) the magnification of any eyepiece without sacrificing image quality or the optical characteristics of the eyepiece. 

Why barlows?  
1) It becomes an inexpensive means to expand your range of magnifications without buying more eyepieces. 
2) And, it allows you to achieve the highest magnification possible for your telescope, especially if the telescope has a shorter focal length.

More than 2x
Traditionally, a barlow increased magnification by 2x. However, today there are also barlows that increase the magnification anywhere from 2.5 to 5 times.

Yes, if you have 2-inch diameter eyepieces, you will need to use a 2-inch barlow.

In the not to distant past (50 or so years ago), barlows had a bad rap because of poor optical quality—that is not so today.

Eyeglasses vs Naked Eye Observing through Eyepieces

If possible, observe without prescription eyeglasses because your observing experience will be more pleasant. If you are unsure about observing without glasses, try it but make sure you focus the image so it is as sharp as possible for a good evaluation.

I continue to hear and read that you need to 
wear your glasses if you have astigmatism.
THIS IS COMPLETE RUBBISH!!!! 
I have astigmatism and I observe without my eyeglasses—it is more comfortable and my images are fine.

Recommendations for those who must wear Eyeglasses.
If you absolutely must wear glasses to observe, try to use eyepieces with rubber eye guards at their tops—it is a good cushion that protects yours eyeglass lenses.

Try to use eyepieces having a minimum eye relied distance of 20mm (15mm is probably the VERY minimum.)

Individuals who MUST wear eyeglasses do have a disadvantage when looking through eyepieces so if you can observe without having to wear eyeglasses, I recommend that you do so—try it. 

Eye Relief
Eye relief usually increases with longer focal length eyepieces that deliver low magnification. An eye relief of 15mm is okay for eyeglass wearers but 20mm or more is even better. Eyeglass wearers need the longer eye relief because eyeglasses prevent getting closer to the top of eyepieces and sometimes, especially for the shorter focal lengths, you have to get real close to see an “appropriate” image.

Long Eye Relief Eyepieces/Sets! 
There are sets of eyepieces that are designed having the same long eye relief for every focal length—these are more or less designed for eyeglass wearers. This eye relief is generally from 15 to 20 millimeters.  Usually, these eyepieces are more expensive. And, usually, you can buy individual eyepieces from sets.

Barlow Magic
Barlows don’t change eye relief. So, a barlow can be used to one’s advantage to increase magnification without changing the eye relief. Remember, barlows do not degrade the optical performance/characteristic of an eyepiece.

Field-of-View Limitations
When you observe with eyeglasses, you will lose some of the larger field-of-view “quality.” Having glasses on limits the ability to look around to the edge of the image an eyepiece can provide. This is one reason why I suggest, if possible, to observe without glasses.

Zoom Eyepieces

My biggest gripe with some zoom eyepieces is that it is not easy to turn the barrel to change the focal length. This can possibly cause marring of the barrel from it turning inside the tightened focus tube.

My very favorite zoom eyepiece is the Tele Vue Nagler 6, 5, 4, 3mm click-stop that I have had for years. The optical quality is superb, it is small and turns easily to change the focal length. Since it goes down to 3mm, it also provides me with the higher magnifications for my shorter length refractors. Its BIGGEST DRAWBACK is its price! Currently (2025), it sell for about $430. 

A Zoom Eyepiece is a single eyepiece that provide​s a range of focal lengths by turning a “ring” on the barrel to change the focal length.

Some Zoom eyepieces have click stops for changing the focal length while others are continuous.

Zoom eyepieces have received mixed reviews over the years because some have had marginal optical quality. However, there are zoom eyepieces with excellent optical quality—so read reviews before you buy.

Popular Focal Length spans of Zoom Eyepieces

1. 6mm to 3mm  •  sold by Tele Vue
2. 8mm to 3mm  •  sold by SVBony on Amazon “GREAT BUY!”
3. 8mm to 24mm  •  various versions from different companies
4. 9mm to 27mm  •  one version sold by different companies

Mechanical Eyepiece Features

Some eyepieces have none of these niceties while others have all of them and are thus more expensive.
It is similar to options when buying a new car.

RUBBER EYE GUARD makes it softer and warmer on the eye when viewing AND is a great cushion/protection for eyeglass lenses.

Some eyepieces have MOVABLE/ADJUSTABLE EYE GUARDS or BARRELS to provide the “positive” placement/position of the eye above the top lens.

SAFETY UNDERCUT to prevent eyepiece from slipping or falling out of focuser when the telescope is moved (especially for telescopes on equatorial mounts). All eyepiece holders have a screw in its barrel to tighten against the eyepiece to prevent slipping/falling out. The safety is a lift that catches the screw if the eyepiece should start to slide out. Don't overtighten this screw otherwise you will mar the barrel of your eyepiece.

CHROME barrels are nice but I have a few black barrels that are fine, too.

Parfo​cal

Parfocal refers to a set of eyepieces that come to the same focus. In other words, you do not have to refocus the set of eyepieces that ​are parfocal when you switch them out to change the magnification. I have a set like this that I very much enjoy because I do not have to constantly refocus going from one eyepiece to another. Now, you might have to very slightly refocus with parfocal eyepieces but you won’t have to crank or turn the focusing knob a lot. This saves times and makes it faster to compare views with different magnifications. 

Parfocal is a mechanical consideration that has to be designed into a set of eyepieces. Generally, a set of eyepieces will be described as parfocal if this is a feature of the set. My parfocal eyepieces are from two different sets of Tele Vue eyepieces—the Panoptics and Naglers series (yes, these are expensive eyepieces but I bought them a long time ago when they were cheaper). Many Tele Vue eyepieces are parfocal across the many different sets this company offers.

Moon Filter  •  It is the only one you really need!

The ONLY eyepiece filter you really need is a Moon filter to decrease the intensity of its “magnified” light.

There are 3 Groups of Filters
1
MOON FILTER to reduce the intensitify of the light from the Moon. This is a necessary filter because you will quickly discover that observing a relatively bright Moon is “hard” on the eye—the telescope concentrates the Moon’s bright light. I don’t think you can damage your eyes lookin at the Moon without a filter but it can “hurt” and you will have a afterglow from the brightness. Ideally, purchase two polarizing filters that can be turned against each other to vary the amount of light coming through. This double type of filter is often sold as a set and often will not come apart (so you can’t accidently drop one of them. HIGHLY RECOMMENDED
2
DEEP SKY FILTERS can help to slightly increase the contrast of some faint nebula and galaxies. I would NOT buy these until you have experience as a visual observer and visual observing is a passion. These filters are expensive and provide only a slight increase in the ability to view some (and just some) fainter objects. The best method to observe fainter objects is to get a larger diameter telescope. NOT RECOMMENDED FOR THOSE STARTING OUT AND A DEBATABLE PURCHASE FOR MORE SEASONED AMATEURS.
3
COLORED PLANETARY FILTERS can very slightly increase the contrast or enhance some subtle features on Mars, Jupiter and Saturn. DO NOT BUY THESE because you can see just as much without them as with them. I have two sets and never use them. 

All eyepieces have threads on the inside bottom of the barrel to screw in filters. 

Filters are available for 1.25 inch and 2 inch diameter eyepieces.

CAUTION
Screwing Filters
onto the Eyepiece 

A. Do not force the filter as you screw it on BECAUSE you can easily damage the threads on the filter or eyepiece (cross threading).

B. Filters should screw in easily. If one does not, check to see if it will easily screw into another eyepiece. If it does not, try a little more force to see if it will screw in and/or try the motion of turning it in and out in small “steps.”

C. I have one set of polarizing filters that easily screws into several eyepieces but will not easily screw into other eyepieces.