A pump zoom, also called a push-pull zoom, is a lens where you change focal length by sliding part of the lens barrel forward and backward instead of rotating a zoom ring. On many designs, the same section may also be turned to focus.

Operation is simple: pull or push the barrel to zoom out or in, much like the motion of a pump-action shotgun.

Pros:

• Fast zooming, especially useful when subjects move quickly
• Historically convenient because one hand could handle zooming and focusing without moving between rings
• Simpler mechanical design

Cons:

• Less precise than separate zoom and focus rings
• Can feel awkward if you prefer dedicated controls
• Often criticized for drawing dust into the lens because zooming changes the lens’s internal volume more dramatically

So the main difference is speed versus precision: push-pull zooms are quick to operate, while two-ring zooms usually offer finer control.