Thin Lens experiment

As always, the data for this experiment can be found on google documents by following this link.

A magnifying lens can be modelled as a thin lens in the physics of optics because its total thickness is negligible in comparison to the radius of curvature for each surface.

For this experiment we used a light box, a paper with a non symmetric cross printed on it, a magnifying lens, and a flat surface to project the image on.

The above image shows the light box and lens combination.
When the ambient lighting is suppressed and the light box is projected through the lens, an inverted image can be seen on the opposite side of the lens.

Though barely visible in the glass, it is possible to see that the reflection of the cross is both vertically and horizontally inverted from the image that appears on the flat box.

The sharpness and size of the projected image was found to be variant with light box distance (object distance) and projected surface distance (image distance). Both measurements are in reference to the center of the lens.

In order to collect data, the light box was placed at a known distance, and the flat surface was moved until a sharp image was formed. The two relative distances were recorded and put into a table. The plot of Image distance vs. object distance follows.

It appears to have a relationship which approximates a reciprocal, however, a plot of their inverses, when summed provides a more thorough explanation.

It is apparent from this graph that the summation of the reciprocal of the two values is nearly constant. Further investigation reveals that the average value for this summation is approximately 1/focal length.