The objective lenses are the primary lenses in a microscope. Other lenses help provide illumination or additional fine focus, but it is the objective lens that provides the majority of the image enhancement. According to Professor John Rodenburg of the University of Sheffield, the objective lens is typically considered to be the most important lense in any microscopic equipment.
What is the Objective Lens?
The objective lens in a microscope is the lens that is closest to the specimen being magnified. Although there are many lenses in the microscope, each of which performs a different type of function, it is the objective lens that contributes the most to enhancing the detail of the specimen. Most microscopes have three or four objective lenses. Each objective lens provides a different level of magnification. The longest lens possesses the greatest magnification power. Since the objective lens is closest to the specimen, it is the farthest from the eye of the observer and provides the greatest magnification.
Objective Lens Types
The objective lens strengths found in most microscopes are the 4x, 10x, 40x and 100x. To calculate the actual magnification provided by each type of objective lens, simply multiply the number before the x by ten. Thus a 4x lens actually shows an object at 40 times its natural size. 10x lenses show an object at 100 times, a 40x at 400 times, and a 100x at 1,000 times magnification.
How It Works
The magnification potential of the objective lens is determined by the ratio between its distance from both the specimen and the image plane. The image plane is where we actually observe the magnified image. For most standard microscopes the image plane is in the eye pieces through which you look. More sophisticated microscopic equipment may also feature a projector which casts the image onto a separate surface. Here it is the focal point from which the image is projected that constitutes the image plane, rather than the eye pieces.