Product description:
Please note: This text was taken directly from the manufacturer.
These anodized, machined aluminum tubes provide extra focuser "back travel" sometimes needed to achieve focus with certain eyepiece/telescope combinations. More back travel is often needed for short-range terrestrial viewing or with use of a field flattener, coma corrector, or focal reducer lens. We offer 1.25" and 2" models, which fit 1.25" eyepieces and 2" eyepieces, respectively. Each adds 2" of length extension. Each also has two locking thumbscrews and is threaded for filters.
