These eyepieces are popular and sell out quickly when they are restocked. Please note that this is the price for a set of three. If you wish to purchase them individually, please comment with the mm size you need on the separate listing. These are famous in the astronomy hobby community for their good performance for the price. They boast a 62° apparent field of view and a comfortable eye relief, and they really do provide a good view. These are recommended, cost-effective, US-made Celestron eyepieces: 4, 10, and 23mm (31.7mm/1.25 inches). In a telescope, these are practical lenses, including the high-magnification 4mm and the low-magnification 23mm, plus the intermediate 10mm lens, which may be the most useful. They are inexpensive because they are imported from overseas. How about taking this opportunity? If you have a telescope with a certain level of performance, upgrading the eyepieces will definitely improve the performance, including ease of use. (Although they are new and unused, I have checked them once with a Vixen R130sf to confirm the quality.) The diameter of the eyepieces is the de facto standard American size (31.7mm/1.25 inches), so they will fit almost all major telescope manufacturers such as Vixen. - Celestron Aspherical 23mm, 62-degree apparent field of view This is a versatile lens. When viewing the moon, planets, nebulae, and galaxies, which do not require much magnification, the 62° apparent field of view provides a wonderful sense of openness and a powerful view. Those who are upgrading from the included lens will be impressed. - Celestron Aspherical 10mm, 62-degree apparent field of view I think this is the most useful lens. By centering the subject with the 23mm and switching to this 10mm, you can observe the details of the lunar craters, the rings of Jupiter, and the rings of Saturn. For the double star Albireo in Cygnus, this 10mm is just right for small apertures, and the orange and blue stars should be clearly separated. - Celestron Aspherical 4mm, 62-degree apparent field of view At this point, it is especially useful when you want to observe in detail. For example, with the 4mm, Saturn will appear with great impact, and you can see the patterns on Saturn itself, the Cassini Division, and the stripes of Jupiter...