By placing an extension tube between the Barlow lens and the eyepiece, you will increase the magnification of a telescope by two three or more times, depending on the size of the extension tube.
The larger the aperture, the more light you can gather, and the fainter the objects you can see or photograph. Telescopes of a given aperture that use lenses (refractors) are typically more expensive than those using mirrors (reflectors) because both sides of a lens must be polished to great accuracy
