Final answer:
The nosepiece is a rotatable part of the microscope that holds and switches between objective lenses, resulting in different levels of magnification. Objective lenses have a range of magnifications and, along with the ocular lens, contribute to the total magnification. The NA, important for light gathering, along with parfocal design and immersion techniques, are essential features of a microscope's objective lens for viewing specimens at high magnification.
Step-by-step explanation:
The nosepiece of a microscope is a rotating component that holds the objective lenses, allowing for changes in magnification. The objective lenses can range in magnification from 4x to 100x and are labeled with their magnifying power. When combined with the ocular lens, which typically magnifies 10x, the total magnification is the product of both the ocular and objective magnifications. Optical microscopes can achieve up to 1500x magnification with a resolution of approximately 0.2 µm.
The objective lenses are crucial in light gathering from the specimen, described by three parameters: the numerical aperture (NA), magnification (m), and working distance. NA is calculated as NA = n sin α, where 'n' is the refractive index and 'α' is the angle of acceptance. Microscopes may employ immersion techniques to enhance NA and are designed to keep the sample in focus when switching objectives, known as being parfocal. The eyepiece, or ocular, works with the objective lens to provide the final magnification and comprises several lenses within a cylindrical barrel. Adjustments for focusing are made possible by the movement of both the eyepiece and the objective lens. Additionally, the final magnified image is visible to us because it is placed at a suitable distance by the microscope mechanics.