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