Optics glass eyepieces for excellent for image contrast and light transmission;give detail and definition across the entire field of view Standard 1.25''/31.75mm fitting diameter, can be used in most astronomical telescopes with a 1.25" focuser Offer high magnifications;look more and more detailed at the moon's surface and other planet; for viewing the moon and planets 4mm 62 degree wide angle aspheric eyepiece can get detail and definition across the entire field of view For lenses with the same refractive the 62 degree aspheric eyepiece is thinner and than the spherical eyepiece