Percent difference clarification

On page 5 of the manual - the percent difference equation might be unclear .. the bottom is supposed to be the "average" of the two numbers. Here is an image of the equation that makes that more clear.

Overview of the Optical Bench setup

Here we can see all the elements on the optical bench. From left to right : the "source" (object) light, a lens in a holder, a second holder (for the second lens), a screen (cardboard).

Light source

The light source should be positioned so that the "screen" is right above the "Zero" of the scale.

Which lens?

The main lens to use is the LARGER focal length (200 cm) of the two lenses.

The Image screen

When we use the light object and the lens to create an image .. this is where we will view the image - on the screen. (All of our images are REAL images .. thus they can be displayed on the screen.

Note : once you get a good image on the screen, try taking the screen away, and put your eye at that location, and look back toward the lens ... can you see a clean image (by looking in toward the lens)? - No, because your eye can't see an image that is right at your eye! You need to move back about 25 cm .. the "near point" for your eye - then you should be able to see the real image that is in space about 25 cm closer to the lens than your head (you have to look "in toward" the lens to see this image).

Location vs distance

We measure all the positions of the various objects (light/object, lens, screen/image) using the horizontal ruler on which the holders slide.

Note : you always measure the POSITION of the things on the optics bench, and then calculate the DISTANCES based on two position values. Thus, the image distance will be the difference between the LENS POSITION and SCREEN POSITION. The object distance = difference between the LIGHT OBJECT and the LENS POSITION.