astronomical optics, part 2: telescope & eyepiece combined
Which Telescope Eyepiece Is Right for You? - Sky & Telescope - Sky & Telescope
Eyepiece - Wikipedia
astronomical optics, part 5: eyepieces
Simple Formulas for the Telescope Owner - Sky & Telescope - Sky & Telescope
How do I use my telescope eyepieces? | Celestron
Eyepiece aberrations 1: spherical, coma, astigmatism and field curvature
Amazon.com : 1.25in Telescope Eyepiece for Astronomical Telescopes, High Medium Magnification Eyepiece for Moon Surface, Planets, Nebulae, Star Clusters, Diffuse Nebulae (25mm) : Electronics