What is a Barlow Lens?
A Barlow is a negative (diverging) lens that is placed between the objective lens (or primary mirror â€” from now on these words will be used interchangeably) and the eyepiece of a telescope. It increases the effective focal length of an objective lens, thereby increasing the magnification. The idea is that 2 eyepieces and a Barlow will give you the flexibility of magnification of 4 eyepieces, and will give higher magnifications with less powerful eyepieces.
While researching my first telescope I have learned the importance of the individual components of the scope. One thing that interested me was the ability to swap eyepieces for your telescope.
Essentially this allows you to alter your field of view and magnification levels on the fly.