15mm focus length eyepiece. 15mm is a intermediate eyepiece fit for observing the lunar surface planets binaries and bright nebula interior. 4 Lenses in 3 Groups: Multiple group lens combination to improve optical performance; the eyepieces delivers sharp images with good color correction and contrast. 16mm eye relief: Generous 16mm eye relief allows comfortable viewing distance and lets eyeglass wearers see the entire field of view. Full multi coated optical and 4-elements in 3 groups allow more light pass through to the eyepieces thus providing a brighter sharper and higher contrast images. This 3x Barlow lens allows you to triple the magnification of any 1.25" eyepiece and deliver stunning image quality without adding a long reach between the telescope and eyepiece. 3x magnification with 1.25" interface. The magnification of the Barlow lens is 3X, which can magnify the image without the Barlow lens by 3 times. You can see more details of the moon and planets, and the image is clear, making your observation more comfortable. The blackening of the edges of the Barrow lens and the internal blackening process can minimize the reflection of light during the refraction process, maximize the saturation and contrast of the image color, and make the image edges clearer. The whole body of this 3X barlow lens is full black metal constructed and precision CNC-machined, which is durable and can be used for a long time.