Sky-Watcher’s 10mm Erecting Eyepiece is 1.25″ barreled and designed to turn upside down images, right side up, when viewed through this eyepiece. This is a common occurrence for many types of telescopes, which isn’t much of a problem looking up at the night sky, but when using the telescope as a spotting scope many people prefer their views to be right side up.
The Erecting Eyepiece can be used on any telescope, refractor or reflector to correct the orientation of the image. The erecting eyepiece can be used on any refractor, even a short-tubed one. It works alone without a diagonal. The extension tube is needed only when focus cannot be reached by using the erecting eyepiece alone. With a reflector telescope, when attached, images are easily corrected while still maintaining their quality and clarity.
This eyepiece isn’t recommended for telescopes with long focal lengths, over 1500, except on the brightest of targets. On telescopes with extremely long focal lengths, the 10mm eyepiece will just be too powerful and the resulting image resolution will be degraded.