Calculating your magnification
Imagine you use a 10mm eyepiece with the focal point of your telescope being 1000mm. Now you have a standard magnification of 100x. With a 3x Barlow lens you will arrive at magnification of 300 x! This is a cost-effective way to achieve a better result. An additional advantage is the ‘flatter’ and sharper image produced by the Barlow lens. A minor drawback is the small optic angle inherent in higher magnifications.