Science Fair Project Relating focus to pinhole size

Question

I am doing a science fair project in which i want to see how the size of a pinhole effects the light diameter, and i would like to also relate this to focus and focal point. How would i do this?

Answer 1

I am doing a science fair project in which i want to see how the size of a pinhole effects the light diameter, and i would like to also relate this to focus and focal point. How would i do this?

Well, since it's a science project, it'd be a good idea to:

1. Learn about the theory involved, and depending on your math skills maybe calculate the pinhole size that you'd need for a reasonably focussed image.

2. Do an experiment! There are plenty of instructions on the web for creating a pinhole that works with a DSLR. If you have access to a DSLR, consider making pinhole lenses with holes of various diameter and compare the images that you get from each.

If the pinhole size that produces the best image matches the size you calculated, that'd be a great confirmation that your calculation was correct. If it doesn't, that might be even better -- you'd then have an opportunity to look at your calculation and try to figure out where you went wrong. Once you think you've found the problem, see if you can devise another experiment to confirm your hypothesis.

This kind of iterative approach, where you keep trying to refine your understanding and check your work with experiments is what science is all about. If you can use science to learn something, and if you present your findings clearly, you're going to be way ahead of the competition. And whether you win or not, in the end you'll have learned quite a bit.

I think this is a great project, actually. It seems simple, but there are a lot of important details. Intuitively, it seems obvious that the smaller the hole, the sharper the resulting image. But that might not really be true -- there might be such a thing as a pinhole that's too small. Either way, a very tiny hole may be problematic for other reasons, like exposure time. Beyond all that, just learning to make a good pinhole will be rewarding. What materials will you use? How will you make the hole? How can you improve the process? Can you make a pinhole that's similar in quality to a commercially produced pinhole? What happens if you change the distance from the pinhole to the sensor? You can take this project in lots of different directions. Have fun!

Answer 2

To really see the effect of pinhole size, I suggest you make the pinhole box large enough to fit yourself inside. Like a broom closet or small toilet size. Make it dark, and make a suitable hole for an old camera lens on one wall, and tape a large white paper on the opposite wall.

For the pinhole I suggest you buy an old cheap short lens. No matter what focal lenght but the physical length of the lens has to be short. Carefully break the glass lenses away, a pinhole camera does not use glass lenses, but the aperture mechanics is what you need. Now, with all optical glass removed the old lens is your adjustable pinhole. You can operate the aperture blades with your finger, there should be a lever of some kind visible on the flange side of the lens. Even better if the lens is all manual and aperture can be adjusted with aperture ring on the outside of the lens.

Attach the broken lens into the hole you prepared, light a bright lamp outside far enough to make it a "point" light and go inside the "camera" box. There should be a circle of light projected on the white paper now. Operate the aperture blades of the "pinhole" to make the hole smaller and larger. Use fog or fake smoke inside the camera box to see light rays in the air for further experimenting with multiple light sources. If there is enough of light outside you'll see even a "picture" of the outside view.