While browsing for cheap second hand lenses I found the Cosina 70-210mm f4.5-5.6. The seller notes that it's a
pump zoom. Googling the term does yield some results, but these simply state that a certain lens is a pump zoom lens, without going into the details. I only found out that these lenses have the focus and zoom control somehow combined in one pumping control (right?).
What is a pump zoom lens? How do you operate it? Are there any (dis)advantages compared to a regular zoom lens with a ring?