How to Change a Telescope Eyepiece

Telescope eyepieces form the magnified images that you see when you look through the telescope's optical tube. An eyepiece consists of lens components in a moisture- and dust-resistant housing. You'll need to purchase an array of eyepieces of differing magnifications, from low to medium and high, to meet your viewing needs. Most amateur astronomers use 3 to 8 eyepieces. Changing telescope eyepieces is a major step in effectively using high-powered optics.

Instructions

Difficulty: Moderately Easy

Things You’ll Need:

• Telescope
• Barlow lenses (optional)
• Eyepieces

Select the Right Eyepiece

1. Select an object magnification result that you want to achieve. You can choose between making small objects, such as stars, bigger or making large objects, such as planets, more detailed.
2. Select an object area that you want to observe. Star clusters or nebulae will require a wide field of view. Moon craters or Saturn's rings will need a narrower field of view.
3. Determine which eyepiece might best suit your objectives. Lower magnification results in smaller objects in a wide field of view. Higher magnification gives you a larger, more detailed image in a smaller frame.

Change Your Eyepiece

4. Loosen the thumbscrew that is securing your current eyepiece until you can move the eyepiece freely. To avoid irreparable damage to the eyepiece or telescope, you'll need to follow the manufacturer's suggested guidelines for your specific model.
5. Slide the eyepiece carefully from the telescope and put it in a safe place, such as a case.
6. Place your new eyepiece inside the telescope and tighten the thumbscrew or other securing device. You are ready to refocus and use your new eyepiece.

Tips & Warnings

• The industry standard size for removable eyepieces is 1.25 inches.
• Eyepieces labeled with lower numbers, such as 4mm, result in higher magnification. Likewise, eyepieces with higher numbers, such as 20mm, indicate lower magnification.
• Change eyepieces less frequently when you use a Barlow, which is an additional 2x magnifying lens that attaches between the objective lens and the eyepiece. Barlows narrow the field of view, but they give greater magnification to what you do see. Many astronomers consider the Barlow a good investment.
• Eyepiece screw threads can jam and stick, resulting in a less-than-tight seal. This can damage your telescope and prevent clear viewing. Make sure your seal is level and tight on the threads.
• Eyepieces can take some time to change and then refocus. Before you change yours, consider which eyepiece to substitute it for rather than picking one through trial and error.
• Excessive cleaning can damage and scratch optics. Clean eyepieces only when absolutely necessary, and only them in a clean, non-dusty environment.

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