Optical Instruments: Simple Microscope

A simple microscope was constructed with two positive lenses and observed. Using the thin-lens equation, the focal length of three given lenses were examined and used to find the angular magnification of the microscope. After the angular magnification was calculated, a to-scale ray diagram was drawn to identify the findings.

1. Introduction A compound microscope has a magnification by two lenses. One of the lenses is objective, which produces a bigger image of the object. The second is an eyepiece lens that is used like a simple magnifier to see the image1. Angular magnification, M, is defined as an angle subtended at eye using an instrument, divided by the angle subtended at “unaided” eye2. In this lab experiment, only the shortest focal length lens and the intermediate focal length lens were used for the eyepiece, as the short focal length was used as a simple magnifier3. The found focal lengths of both the shortest and intermediate lenses were 6.5 cm for the short one, and 11.4 cm for the intermediate.

2. Experiment In order to find the focal lengths, four trials were made of finding the object and image distances that gave the clearest image of the light source on the screen. After four trials were done for each of the three lenses, the thins lens equation was used to calculate their focal lengths, which then gave us an average value for each. Using the shortest focal length and the intermediate, the microscope was made by placing the magnifying lenses at different distances to the screen. Then, a ruler was taped, which would serve as the object seen in the microscope, to a white sheet of paper and onto the viewing screen.

Figure 1: The diagram shows the measurements made, which included the distance from the eye to the first lens, distance from the eye to the screen, d, the height, ho, of the object,