I was surprised by this explanation describing how the beam is focused:

Optical tweezers are capable of manipulating nanometer and micron-sized dielectric particles by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. ...

I imagined something more complex, although what exactly I'm not sure.

Are there any other ways of doing it? Are off-the-shelf microscope lenses used routinely, or are custom lenses the norm?