Why would one use an objective marked LWD or ULWD?
The letters identify a long working or ultra-long working distance objective. The vertical distance from the front lens of the objective to the focused specimen (working distance) is much longer than that for a similar magnification standard objective. Such objectives are invaluable for looking up through a culture vessel or Petri dish in inverted biological microscopy; or examining IC wafers to prevent inadvertent contact with the wafer; or inspecting solder connections of mounted chips.
