How Do You Use Telescope Eyepieces

How Do You Use Telescope Eyepieces?

You have a newly bought telescope, welcome to the celestial side! Naturally, you would want to know everything there is about it.

For a comprehensive knowledge of a telescope, you need to start from the basics. The Eyepiece is one of the most basic integrations in a telescope.

What is an eyepiece for a telescope?

Eyepieces are necessarily magnification tools in a telescope. The parameters of an eyepiece differ for different objects.

Objects such as a star cluster are best viewed at high magnification. In contrast, planet bodies appear tiny at higher magnification.

It is not the ultimate factor that decides how well your observation turns out. But the diameter of the Eyepiece is what determines the magnification.

Calculate some essential parameters of the Eyepiece

Here is what you need to determine before using an eyepiece:

Determining the Magnification

The defining factors of an eyepiece include the focal length and apparent field of view. But the dilemma is to figure if it’s the right configuration for your telescope.

How do you deduce the resultant magnification? As complicated as it sounds, it is easy maths. Divide the telescope focal length with the eyepieces focal length.

Determining the True Field of View

Two closely related factors form the practical context of a telescope. The Apparent field of view and the real field of view.

Apparent is the width of the view through your Eyepiece. It is this measurement of an eyepiece that is advertised.

The true field of view is the width of the Eyepiece and telescope paired. The concept behind the two fields of view is quite transparent.

The true field of view is called ‘true,’ as you won’t just be tinkering with the Eyepiece. It is easy to calculate the true field of view.

You need to divide the Eyepiece’s apparent field with its magnification. This number lends you a practical insight into the size of the celestial objects.

Important considerations before using a telescope’s Eyepiece

The know-how behind telescopes is an essential step for using the telescope. Every Eyepiece is unique in terms of diameter.

Eyepieces are available with different powers. The higher the calibration, the lower will be the power and vice versa.

We recommend that you begin with an eyepiece with low power. Such an eyepiece can be focused easily and offer a wider field of view.

For more general observation, low-power eyepieces are better preferred. The resultant imaging is bright and crisp.

With the increasing power of an eyepiece, the image’s sharpness is compromised. High power eyepieces are employed for binary and lunar stars.

How to use a Telescope Eyepiece?

Using an eyepiece is remarkably simple. But before we get into the mechanics, there is one more accessory worthy of mention.

The Barlow’s Lenses

Barlow’s lenses are still considered one of the most robust scope accessories. Barlow’s lens is placed between your telescope’s focuser and the Eyepiece.

The placement of these lenses results in a magnification of an eyepiece. The magnification can two times or three times.

If your Eyepiece has a longer focal length, a Barlow’s lens becomes a necessity. It reduces squinting and gives your eyes the needed relief.

Barlow’s lens is a versatile device, but it does affect the visuals. You can experience a blur while using it with a high-powered eyepiece.

Barlow’s lenses are not functional for astrophotography. Try using the Eyepiece without the lens. If you don’t get the desired result, supplement it with the lens.

Using a Telescope Eyepiece

Insert the lower-power Eyepiece in the telescope. Adjust and tighten it firmly in place.

Peek through the Eyepiece. Place the Eyepiece right behind for less eye strain.

Never place your eye directly in front of the Eyepiece. If you get too close, it is harder to blink. This will create a virtual black ring in your field of view.

Ensure that there is a distance of at least 15mm in between. Placing the eye at a larger distance than 15mm is not right. It will distort your field of view.

Turn the knob right below the Eyepiece. Turn the second knob until the celestial object is in your focus.

You can also try using different eyepieces. Change the power of the Eyepiece until you get the desired result.

Repeat the above steps until you get the object back into focus. You can also try supplementing the Eyepiece with a Barlow’s lens.

Remove the Eyepiece and insert the Barlow’s lens. Reinsert the Eyepiece. Again, follow the steps mentioned above with the new system.

Recommended Reading:


  1. High Point Scientific
  2. Optics Planet
  3. Ozscopes
  4. Starizona
  5. Celestron