Final answer:
The lenses with interchangeable magnification on a stereo microscope are objective lenses, which are responsible for the initial magnification of the specimen and can be changed to adjust the total magnification level.
Step-by-step explanation:
The lenses on a stereo microscope that have interchangeable magnification are objective lenses. On a stereo microscope, the objective lenses are responsible for the initial magnification of the specimen. The eyepiece lenses, or oculars, then further magnify this image. Therefore, by changing the objective lens, the total magnification of the microscope can be altered. A compound microscope typically has multiple objective lenses with different magnifications that can be rotated into place to view the specimen at different levels of detail.
To provide a clear example, if a microscope has a total magnification of 800x and the objective lens provides a 200x magnification, the eyepiece lens must therefore provide a 4x magnification (800 / 200 = 4). If other objective lenses with magnifications of 100x and 400x are available, when used in conjunction with the same eyepiece lens, total magnifications of 400x (100 x 4) and 1600x (400 x 4) can be achieved respectively.