If you’ve ever tried wearing glasses while looking through a telescope, you know it can be a bit… awkward. So maybe you’ve asked yourself: Do I even need to wear them during my observing sessions?
The answer depends on what type of vision problems you have:
- If you are only nearsighted or farsighted, you don’t need to wear glasses when looking through a telescope. Your telescope’s built-in focuser will still be able to bring objects into sharp focus.
- If you have astigmatism, you may need to wear glasses (or contact lenses) when observing. This is because your telescope’s focuser is not able to compensate for astigmatism.
Astigmatism: When should you wear glasses?
People with astigmatism generally need to wear glasses or contact lenses when observing under low magnification. However, glasses are often not needed at higher magnifications because the effects of astigmatism are reduced. You can learn more in my article on calculating magnification.
The reason for this has to do with the exit pupil, which is the cylinder of light that exits from the eyepiece and goes into your pupil. Higher magnifications have smaller exit pupils, which means the light doesn’t pass through the most distorted parts of your eye’s lens.
The problem with wearing glasses while observing
Although wearing eyeglasses may be unavoidable for some people, it’s worth noting that they can make observing more difficult. The biggest problem is that the glasses force you to keep your eye farther away from the eyepiece, which can significantly limit your field of view.
There are a couple of solutions to this:
- If you have contact lenses, you can wear them instead.
- You can buy eyepieces with long eye relief (more on this below).
What are “long eye relief” eyepieces?
A long eye relief eyepiece is designed so that you can comfortably view while staying farther away from the eyepiece. It will allow you to get the eyepiece’s full field of view – in other words, it won’t feel like you’re observing the skies through a paper towel tube.
These eyepieces tend to be a bit more expensive, but as I noted in my article on Barlow lenses, adding a Barlow lens will allow you to get two different magnifications with the same eyepiece. This way you can get more use out of your eyepiece.
Below are some examples:Orion Edge-On Planetary Eyepiece
The Orion Edge-On series is one of the more affordable long eye relief eyepieces. It is mainly designed for planetary and lunar viewing, but can of course be used for deep sky objects as well. All of the eyepieces in this series have 1.25-inch barrels, which means they can be used with almost any telescope.Baader Planetarium Hyperion
Baader Hyperion eyepieces have a wide apparent field of view (AFOV) of 68 degrees. Generally, the Hyperion line has 1.25-inch barrels (with a built-in 2-inch upper barrel), so they can be used with almost any telescope – although a couple of their high-focal-length eyepieces have 2-inch barrels.Tele Vue DeLite
Tele Vue eyepieces tend to be very expensive (and high-quality), but their DeLite eyepieces are relatively affordable. They were designed to be a cheaper version of their Delos eyepieces, which also have long eye relief. However, the DeLite line is still more expensive than the Orion Edge-On or Baader Hyperion lines.Vixen Lanthanum
Like the Tele Vue DeLite, the Vixen Lanthanum is a bit on the pricey side. But in addition to having long eye relief, it also has a wide apparent field of view of 72 degrees – slightly wider than the Baader Hyperion.
Ed Ting has some more tips on choosing long eye relief eyepieces:
A final thought
If you ordinarily wear glasses, make sure to bring them with you when you observe the skies – even if you don’t plan to wear them when observing though your telescope. Part of the fun of observing is taking in the whole sky at once with the naked eye. Without your glasses (or contacts), you won’t be able to see nearly as many stars; the tiny pinpricks of light will become blurrier and dimmer.