The Tele Vue 2x 1.25" Barlow is a top-quality lens designed to double the magnification of any eyepiece. Simply insert the eyepiece into the top of the 2x Barlow, and get an instant power boost.
Tele Vue insists on nothing less than the best fully multicoated optics, using high-index glass to deliver the highest light transmission and best contrast of any Barlow, with less off-axis false color than 3-element Barlows.
The focal length of the eyepiece is divided by 2, so a 25mm eyepiece becomes 12.5mm. The field of view is also halved.
Many astronomers prefer using lower-powered eyepieces with a Barlow to higher-powered eyepieces, due to being more comfortable to work with.