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Its important to have a range of magnifications when it comes to selecting eyepieces. You should have at least three eyepieces in the following ranges. Low: 25mm-30mm, Medium: 10mm-15mm, and High: 3mm-5mm This will set you up with the basics. Higher magnifications are better on bright objects like the planets and the moon. Lower magnifications are generally better for deep space objects like nebula and galaxies. Remember that it’s the size of your primary optic that determines how much you can see in an object, not how much you magnify it.

BARREL SIZE

The silvery metal ring on the end of an eyepiece that sticks into the telescope’s focuser is called the barrel. Most eyepieces on the market today come in two standard barrel sizes, the 1.25” and 2”. You want to make sure that the scope you choose can handle either or both of these barrel sizes. There are still some budget telescopes available with the old .965” barrel size but they are much less common. As long as you chose the standard sizes today you wont have an issue finding upgrades and accessories to fit your equipment. There are adapters to mate a 1.25” barrel to a .965” focuser but because the barrel of the 1.25” extends the eyepiece farther out from the focal point of the telescope, you may have issues getting it to focus. Its just best to upgrade from a .965” system to the current standard.

COATINGS

A term to look out for in eyepiece specs is the word “multicoated”. Eyepieces are coated with a special coating that helps transmit light through the glass. A multicoated eyepiece simply means all the elements inside the eyepiece are coated with this special light transmission coating. When cleaning eyepieces you must take great care not to use a rough cloth or harsh chemical that could destroy the coating on the surface of the lens elements.

CLEANING

Cleaning kits for eyepieces can be purchased from astronomy dealers. Its probably the wisest way to go if you feel you need to clean your equipment. A camera lens cleaning kit may also work. Be gentle with your expensive eyepieces and treat them delicately. Its good to adopt a “no touch” policy and keep eyepiece dust caps on when you are not using them.

If your eyepieces dew up while you observe, simply let them set out to dry inside your house till the moisture can evaporate. A hair dryer can speed the process up. Blow only enough warm air over them for the dew to evaporate and not to make the eyepiece too warm.

EYEPIECE TYPES/BUYING EYEPIECES

While searching for eyepieces you may come across names like Orthoscopic, Plossl, or Nagler. There are a lot more to name but they are all simply referring to the internal design of the lens elements and sometimes even their designer. Some eyepieces are indeed better than others in how they handle light. Their prices can range from $50 USD to even $600+ USD. There are good reasons to spend a little money on a quality eyepiece but a basic $50 Plossl will do the job. If you are looking for new eyepieces I suggest visiting a major star party or local astronomy club to talk to amateurs there about eyepieces they use and like. They will even usually let you take a look through their equipment. It’s a great place to try before you buy.

EYEPIECES: BASIC KNOWLEDGE

EYEPIECE MAGNIFICATION/FOCAL LENGTH

One of the first things you might notice when you take a look at an eyepiece is the “mm” number printed on it. It might say 25mm, 15mm, or 7mm. This number gives you the focal length of the eyepiece. Focal length is basically the distance it takes light to focus to a point (focal point) from the lens. Its fairly important because you can use this number to figure out the magnification for an eyepiece used with your telescope. To find magnification, simply divide the telescope’s focal length by the eyepiece’s focal length. You can usually find your telescope’s focal length on the specification/identification tag located on the telescopes tube near the eyepiece rack. It will be a much larger “mm” number.

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Ft / Fe = M

EX: 1200mm / 15mm = 80X

MAGNIFICATION FORMULA

Telescope Focal Length = Ft

Eyepiece Focal Length = Fe

Magnification = M