The scanning objective is typically the lowest power objective lens on a microscope, usually marked as 4x. It is specifically designed to provide a wide field of view and is used primarily for locating specimens on the slide before switching to higher power objectives for more detailed observation.
When using the scanning objective, you can quickly bring the specimen into focus and get an overview of its structure and layout. This is particularly useful for identifying where to look more closely with the higher magnifications available in the microscope. In many cases, the scanning objective will have a shorter working distance, allowing the user to maintain a safe distance from the slide while achieving an initial focus.