Let me guess – your new to the world of Astronomy and just need some straight answers! What eyepiece should you get for your telescope? What’s a Plossl? What’s the difference between a 3 element and four element eyepiece? What’s an 8 element eyepiece?
Well, this guide has been especially written with your questions in mind.
Is there something wrong with my eyepieces?
Possibly. All manufacturers we know include eyepieces along with your telescope. We are hoping you haven’t purchased a ‘department store’ telescope, but if you have, chances are you ended up with a Symmetric Ramsden (SR) or a Huygen (H) eyepiece (both 2 element eyepieces) bundled with an overpowered, poor quality x3 barlow.
The problem is the eyepieces are unpleasant to use and often severely overpowered. Using a SR4mm on a rickety yoke telescope is a recipe that has put many a child off Astronomy for many years, which is why we get cranky when we see them. If you spent less than $150 or so on your telescope, honestly, you may be best off quietly disposing of the scope and getting a proper one before the damage is done. However, if the telescope you bought has a decent, non-yoke, non EQ, AZ3 type mount it may be salvageable. (We don’t mean to be unkind – a yoke telescope is notoriously unstable, an EQ mount is horrible to setup and use for a beginner, as the complications in setting it up to track the stars are just so difficult, while a simple AZ (altitude up/down, azimuth left/right) is just so, so much more easy to use).
So, what type of eyepiece should you get? Get a decent 3 element (such as the Kson Kellner’s), or four element (either Plossl or Orthoscopic) eyepiece. They make a world of difference and are inexpensive. They are tremendously good eyepieces and will get you 90% of the way toward solving your eyepiece problems. If your telescope accepts 2″ eyepieces, a set of Kson 2″ Kellners can provide amazing views for very little.
What focal length should your eyepieces be? We recommend a decent range, a 32mm, 20mm and a 7mm eyepiece with a quality barlow is wonderful. The 32mm eyepiece will let you sweep the sky and see large asterisms, nebulae and really enjoy the sky. The others will allow you a bit of ‘zoom’ for some objects and add to the excitement. The higher powered 7mm is terrific for getting right in close. When you add a decent barlow to the mix, you will end up with all the focal ranges you could reasonably need. The 32mm becomes a 16mm, the 20mm a 10mm, though we wouldn’t use a barlow with the 7mm unless you want to see some moon craters up close.
What’s a Plossl? – A plossl is the name of a 4 element eyepieces. They are a great design and are what you should be using if you are not using an enhanced 3 element kellner design.
What’s the difference between a 3 element and 4 element eyepiece? A 4 element is usually better corrected – which means it gives an improved view. We say usually, because there are unusually good 3 element eyepieces that have been created with real care and feature things such as multi-coatings, baffling and may have excellent manufacturing / build properties.
What’s a five element eyepiece? 5 element eyepieces are often called ‘Erfles’. Many decades ago, some truly awful ones were made, and gave them a terrible name. This is not the case anymore. One of the most expensive brands we carry, Masuyama use a 5 element design, and the Kson 26mm 5 element is absolutely extraordinary. This design however, works exceedingly well with longer telescope refractors, reflectors, especially short reflectors, not so much. If you have a longer telescope, try one – you will be amazed. The longer your telescope, the better the view will be through one of these.
Are all eyepieces of the same type, or number of elements, the same? No – the quality of the manufacturer really makes a difference. Many cheaper Plossls say they are ‘coated’. That’s nice – but it’s not fully coated. And fully coated isn’t multi-coated. Believe it or not, but the coatings can be far more crucial than the type of glass that is used. On top of that, an eyepiece should be baffled to reduce stray light in the eyepiece and prevent unpleasant reflection problems. Some manufacturers even go to the extreme of blackening the edges of the glass in the eyepiece. Fujiyama’s Orthoscopic eyepieces are an example of ones that do this. In some cases, a quality Kellner can exceed the performance of a Plossl. Kson’s 10mm and 25mm were reviewed and found to be better than many Plossls at a very cheap price.
If you’ve enjoyed this article, please check our “Which eyepieces should I get” guide, which is specific about your eyepiece options, and some sensible strategies for selecting a perfect eyepiece set.