AmScope WD165 0.5× microscope (auxiliary) objective / Barlow-lens

The WD165 0.5× is a 0.5× auxiliary objective lens (sometimes called a Barlow or auxiliary lens) used with stereo microscopes.

It halves the magnification of the mounted objective/zoom head (so you get lower magnification) while increasing the field of view.

It also gives a long working distance — “WD165” refers to ~165 mm working distance.