Laser Beam Expanding Telescope 

Translating, not a rotating, telescope.

Zoom Telescope

The primary advantage of a beam expanding laser telescope in an industrial laser tool is shrinking the focused spot  which then greatly increases focused power density.  For example a 3.3X beam expansion shrinks the spot by 1/3 thus providing an order of magnitude (10X) increase in power density.  Since it is power density that your part "feels", this is significant.  Getting the equivalent by raising your maxed out laser power by 10X is generally either impossible or very expensive.  A telescope is a cost effective method to improve laser processing. Typical expansion ratios are 3X, 5X, and 8X. 

This zoom telescope works in combination with video viewing in the sense that the telescope compensates for chromatic aberration.  In other words you do not have to worry about the focal difference between best visual focus and best laser focus.   

Thus, beam focus is independent of camera focus.  So you can vary laser spot size while remaining in visual focus at all times. This means you can swing the beam focal point above and below the video viewing plane.

If your application, for example volume production, has no need for video viewing, you can still justify a telescope on the basis of spot size reduction. Laser spot is reduced inversely proportional to beam expansion.  A 3X beam expander reduces spot size to one-third (1/3) while raising focused laser power density nearly 10X as mentioned above.