The revolving nosepiece of a microscope is called the turret. The turret is the part of a compound microscope that holds the objective lens. It can be rotated easily to switch between lenses of different powers.
Most compound microscopes have four objective lenses of 4X, 10X, 40X and 100X powers. These lenses produce magnified images of specimens when coupled with the eyepiece lens. Images at 40X and 100X powers should be viewed through a condenser lens for optimal resolution. This lens, also known as an Abbe condenser, creates sharper images by controlling the amount of light that goes through the specimen.