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What is the relationship between focal length in millimeters to magnification power? I'm looking for 25X eyepiece w/ long eye relief. Which XW Pentax? — 2 Answers

by John, from WA, United States Asked on February 22, 2020

Name Pentax XW Extra Wide Fully Multi-Coated Eyepiece (5)
$372.82 $349.00 Save Up to 25%
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Answered by CosmoVT, member, from VT, United States, on February 18, 2021

Take your focal length in mm and divide by the focal length of the eyepiece. So, if your telescope is a 650mm focal length and your eyepiece is 20mm: 650/20= 32.5. The 32.5 is the magnification. You could also divide your telescope focal length by the magnification you want to see what size eyepiece you would need for that magnification.

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Answered by Victor, guest, from FL, United States, on January 03, 2021

To determine the magnification of your telescope, simply divide the focal length in mm of your telescope by the mm of your eyepiece. For instance, if your primary mirror or objective is 1500mm and your eyepiece is 20mm, divide 1500 by 20 and you get a magnification of 75x. Hope this helps.

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