Working With Lenses: Lab Report by Seth Dowler and Ryonell Frederick

Abstract
Students will learn to build and utilize various telescope modifications for the purposes of viewing distant objects.


Introduction
From simple to complex, telescopes allow for the sometimes simple and sometimes profound explorations of humans working to identify what lies ahead within the world and within space. Therefore a greater understand of their properties and functions is essential to understanding many discoveries of astronomers within world history.


Procedure
First,. for parts A and B, we identified our lens kit number: 3. Then we placed each lens on top of a meter ruler, so as to allow our light source to pass through the lens and onto a sheet of paper. We recorded (in centimeters) the focal point, image size (the length of the image projected onto the paper), the brightness of the image, and the orientation of the image. We repeated this process for all the lenses of the kit and answered the questions copied below.


For part C, we proceeded to create telescopes out of our lenses. We did so by creating an astronomical refractor type of telescope. This is done by mounting each lens at the end of the telescope tube via the tube rubber -- the convex lens with the longest focal length was used here -- this piece is referred to as the objective lens. Then the convex lens with the shorter focal length was used as the eyepiece. Using this telescope, we observed objects down the hallway outside our class and recorded our observations of them.


The point of this was to estimate the magnification of each lens modification first, then to calculate them from our recordings -- this is done through the formula M = fO/fE. M is magnification; fO is the focal length of the objective lens; fE is the focal length of the eyepiece lens. We calculated the magnification of each different setup with each lens. Lastly, we also recorded the orientation of each setup's resulting images.


For part D, we repeated the process of Part C except with the concave lense as our eyepiece (which creates a Galilean refractor rather than an astronomical refractor).


Results and Discussion


Parts A and B

The results of our experiment, corresponding to each description of the 4 lenses tested, are copied below:

Thicker convex lens

3.7cm focal point

1 millimeter image size

Quite bright image

Orientation = upright

Thinner convex lens

6.6cm focal point

1 millimeter image size

Seemed a little brighter than the thicker convex lens

Orientation = same

Concave mirror

8.3cm focal point

6 millimeters

Brightest of all lenses tested

Orientation = inverted

Plane lens

48.8cm focal point

4 millimeters

A little less bright than the 2 convex lenses

Orientation = inverted


*E. the convex mirror most closely resembles the properties of the convex lens.
*F. when covering the lens, the brightness and clarity of the image stay the same but the iamge is cut in half due to an eclipse of its light source.

Part C

Thicker convex lens

6-7x magnification estimate

Orientation: inverted

52.4cm focal point

Calculated magnification = 14.2x [formula = 52.4 / 3.7]

Thinner convex lens

4-5x magnification estimate

Orientation: inverted

55cm focal point

Calculated magnification = 8.3x [formula = 55 / 6.6]

Part D

Concave lens

3-4x magnification estimate

Orientation: upright

46.8cm focal point

Calculated magnification = 5.6x [formula = 46.8 / 8.3]

*this type of refraction (Galilean) is different from the others (Astronomical) in that it does not invert the images it produces.

Conclusion

This lab allowed us to better understand and appreciate the intricacies and innerworkings of telescopes: both astronomical and Galilean types as well. Additionally, we came to know the meaning of magnification on a deeper level than we had before the lab through our calculations involving the formula M = fO/fE. Lastly, by projecting light through the lenses and recording the brightness, focal length, and orientation of the images produced, we furthered our understanding of the ways in which varying lens types affect the images they produce.