Final answer:
The white ring typically refers to oil immersion in microscopy or marks on camera lenses indicating depth of field, which is controlled by the aperture. In this context, the white ring is associated with controlling the depth of field in photography.
Step-by-step explanation:
The student has asked about a lens with a white ring, often associated with the immersion objective on a microscope or a camera lens in photography. This white ring symbolizes oil immersion, which is used to increase the resolution of the image by allowing more light rays to enter the objective. When discussing camera lenses and the phrase 'white ring', it may refer to understanding the concept of the aperture, which controls the amount of light that enters the camera and affects the depth of field.
In photography, a large aperture (denoted by a smaller f-number like f/2.8) results in a shallow depth of field, where the subject is in focus, but the background is blurry. A smaller aperture (larger f-number like f/16) results in a greater depth of field, where more of the image is in focus.
Therefore, based on the information provided about photography and lenses, the correct answer to the student's question 'Immersion (largest lens), white ring = ... ' is 'C. Depth of field', as this is influenced by the setting of the aperture. The white ring does not relate directly to aperture, focal length, or shutter speed, but the question contextually implies that it's related to depth of field in photography.