A previous post of mine was on the topic of the Camera Obscura, a forerunner to photography and camera technology. Our granddaughter used the idea to create a project for her school science fair. She obtained three images which were excellent examples of her results. As a proud grandparent, I get to boast.
Camera Obscura is a simple device consisting of a light-tight box with a hole in one wall. The hole allows inverted and reversed images to be cast on the opposite wall. The box can be small or as large as a room. The image below is the basic idea. She used her bedroom as the box.
First, she covered both windows to darken the room. In the center of the cover on one window, she had an aperture to let light into the room. She made three different sizes of interchangeable apertures of diameters from about 1.0″ down to 0.5″. She hypothesized the different sized apertures would produce images of different sharpness. A digital camera was placed on a tripod near the aperture pointing at the opposite wall in order to record the images for analysis.
This first image recorded the result of the largest aperture of about 1.0″. The ghostly image is actually two scenes. There is a bedroom door at the left with the dark doorknob. In the center are two clothes hooks. At the right is a dark dresser with a lamp on top. Superimposed on that scene is the inverted-reversed outdoor scene. There are tree branches and some other things hard to distinguish.
Next is the image using the medium aperture of about 0.75″. The bedroom elements are still the same. The outdoor scene now shows a picket fence, children’s slide, and a step ladder. The tree branches are in sharper focus.
Lastly, we see the image using the smallest aperture of about 0.5″. Notice the improvement in sharpness of the outdoor scene. The tree branches in the far trees are quite sharply focused.
As photographers know well, smaller apertures sharpen the image. It explains why brightly lit scenes are easier for our eyes to focus. Our iris apertures become smaller to limit the amount of light on the retinas. It also explains why squinting helps our eyes focus. We are making a smaller aperture.
Excellent project, granddaughter!