Eyepieces

Eyepieces are essential parts of a telescope. With different eyepieces, different zoom levels may be achieved. Eyepieces are interchangeable, and thus, may be used from one scope to another. It is always advisable to invest on a good one, since you may still be able to use it in case you have finally decided to upgrade and buy a new and larger telescope.

New telescopes are usually supplied with 2 eyepieces, one is ‘hi-power’, which will show zoomed-in views, great for close-up views of planets, the other one is a ‘low-power’, which shows zoomed-out views, intended for observing deep-sky objects. Below are eyepieces supplied in one of my telescopes:

Pair of eyepieces, one low-power (left), one hi-power (right)

The magnification of a telescope’s view depends primarily on the ratio of the focal lengths of the objective lens and the eyepiece lens, and follows the formula:

Magnification = Focal length of the objective / Focal length of the eyepiece

At F=900 mm, the focal length of my telescope,  the 25 mm and the 5 mm eyepieces shown above provide magnification of 36x and 180x, respectively.  Should you need provisions for varied zoom levels, you need to buy more eyepieces. Just make sure you buy one with a different focal length. We do not want to have duplication of eyepieces as it would defeat the purpose.

From left to right: 17 mm, 25 mm, 6 mm, 40 mm, 20 mm

Different objects require different zoom levels. For example, deep-sky objects like nebula or galaxies are best viewed at low-power, while craters, double stars, and planets are best viewed at high power.

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© Anthony Urbano (Manila, Philippines)

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5 thoughts on “Eyepieces

  1. Can you please guide me if I want to observe planets like Jupiter, Mars, Saturn, what eyepiece would be suitable with Skywatcher Dobsoninan 10″ ? I have 2x barlow, If I wish to further magnify an image of planet, can I add another 2x barlow on top of existing barlow? example 2x barlow with 10mm eyepiece, can I add another 2x barlow to enhance the view?

    • I think what you have right now will do just fine, and no need to acquire new eyepieces. Just try viewing the targets using the low power eyepiece first, and then with the high power eyepiece. Then use the Barlow only if you wish to see higher magnification. I recommend stacking together only up to two barlows, or better yet, simply use just one Barlow with higher magnification (using one 4X Barlow is better than stacking together two 2X Barlow). For more information about Barlow lenses, click here.

      Good luck!

      • For the specs of your telescope, the 6 mm should be a good investment. It should yield a higher magnification (larger image), and with a larger image, you’ll likely see more details (considering that you have 10 inch of aperture). Good luck!

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