Pinhole Camera

Okay, so it's not like I don't have enough random interests. But teaching in a physics department provides a diverse instructional load. One day I'm teaching about rivers and streams and the next day I'm teaching about the resistivity of Nichrome wire. The 2nd semester physics class is starting to talk about light. One of the biggest everyday experiences people have with light (aside from it being "day" and there being sunlight by which people can see...) is via cameras and lenses.

In order to understand some of the basics about lenses and optics, "pinholes" make a good start. Plus, it's easy enough to build a pinhole viewer (or "camera") from everyday items. The idea is to get the image projected from the pinhole to light up a "screen" and make the surroundings dark enough to see the resulting projected image.

The "cardboard tube pinhole camera" has many varieties. But I decided to try my hand at upscaling the project. Just like sedimentary particles, it's always fun to go big, so I made a bigger one that zooms in and out, changing the apparent magnification of the image:

Here's the completed Pinhole Zoom Viewer.


I was fortunate to have two thick cardboard poster tubes that nested inside each other, This made it easier to assemble. You could make nesting tubes by rolling tagboard or heavy paper, but there would be some additional work to smooth out the seams so that extra light won't leak in.


To start, gather the necessary materials: two nesting cardboard tubes (light-proof), a sheet of aluminum foil large enough to cover one end of the large tube, a sheet of wax paper (tracing paper might work too) to cover one end of the small tube, and some tape. You may also need scissors, extra black construction paper and stuff to "pimp out" your viewer.


Cover one end of the large tube with aluminum foil. Keep the foil taught (like a drum head) over the tube's opening. Tape it down so that no light can get in around the sides. Cover one end of the small tube with the wax paper - this is your projection screen. The "screen" end goes into the bigger tube. Make sure there's enough space to slide it in, but not so much that light can get in around the edges (sense a theme here?). Now take a narrow pin, or paper clip, and punch a narrow pinhole in the center of the foil. This pinhole should be somewhere between 0.5 and 1 mm in diameter (check the web for further discussion on the pinhole diameter - and discussion about making the foil more effective).

The reason for the long tube between your eye and the image "screen" is so that it's dark. You can fashion a "hood" around the viewport to block even more light with additional construction paper, as I did with my version. Although if you snug the tube up to your eye, you can probably get it to work okay.


Since the projected image is of a certain size, by extending the tube, you effectively "zoom" in on a small portion of that image, increasing the apparent magnification (this is part of the reason why "zoom" lenses on cameras do what they do). To take in a wider view, push the tube in. This typically works best outdoors in bright sunlight - although you can see the effect by looking at a light source (like a light bulb or candle) indoors.


Here's a quick test I did by placing my zoom viewer on top of a digital camera and lens (exposure time of a couple of seconds at ISO 800). You could try to place the pinhole viewer directly on the camera body (without lens), but if you're not familiar with how to keep the image sensor clean, you might want to hold off on that step. My next test images will probably be to set up the viewer on a tripod and take a picture of some objects outdoors (but the rain today and tomorrow will probably delay those plans).

Anyway, this project seems to work well for "kids" of any age. Even cynical college students get a kick out of seeing an image through these things. And it only takes a few minutes to build the simple ones.

UPDATE (10/12/2010): I have another post about turning your DSLR into a pinhole camera.

Another Random Thot

Comments from Stephen Hawking regarding contact with intelligent extraterrestrial life have been making the rounds lately.

My own take on this is that this idea is somewhat moot. Any intelligence sufficiently advanced to strip our planet of resources is likely to discover us regardless of our own efforts. That's also assuming that any intelligence wants anything to do with our little rocky pebble tucked in the western spiral arm of the Milky Way galaxy...

The Yardbirds

Not the Clapton/Beck/Page rock band, but rather birds in the yard. Specifically, my yard.

We put up a bluebird box this spring, and we've had a few pairs of bluebirds checking it out. I don't know if it'll pass muster, but I did manage to get a few shots of the potential homeowners:





I figure this is a nice salve to calm my righteous indignation as a result of the previous post....

Random WTF?

Pharyngula has a link to an article about marital sex obligations written by a 'minister.' He was pointing out the unfortunate analogy in equating marital sex to cleaning the toilets - as in, "it has to be done."

As I said, sometimes sex is just sex; it's what you do when you are married. Just like cleaning the toilet is what you do to keep your house clean...and I bet you don't have this great desire or huge emotional connection to scrubbing the porcelain! You do it because it needs to be done and that's the way it is with married sex... it does need to be done! It's the glue that God gave us to bond us to one another. The bible is very clear that it is your responsibility as a spouse. [Emphasis mine]

So what we also have here is a command by someone in at least a perceived "position" of authority (ahem), that the spouses must have sex. Well, that's all well and good until you get to the point where one spouse does not want to have sex. There's another word for making someone have sex against their will - it's called rape. So all guffawing about the stupid analogy aside, ignoring the patronizing christian themes of marriage and chastity, there is a very worrisome undercurrent here. That one spouse has the authority to force the other to do something. That's not marriage, it's not love, it's abhorrent.

Braided Streams of Yore

The image above is from Dunn County - along the Lower Chippewa River in western Wisconsin. The dark squiggly lines in the farm fields are the remnants of braid bars. If you look at an image of the Lower Chippewa River today, you will note a distinctly meandering pattern. Why the change? Largely due to the input of sand and gravel from the big ice sheet about 20,000 years ago. All that shifting sand helped create an unstable river bed. Couple that with highly episodic flow and you have the main ingredients for a braided stream morphology, rather than a meandering one. Now that the glaciers have gone, the sediment supply is diminished, vegetation has helped stabilize the banks, and the river is cruising around a single, meandering channel.

Odd spam

I've been getting links to questionable asian language sites that likely cater to folks with certain proclivities. I don't know how it's getting past the captcha system, but I'm glad I review comments before posting them.

In other news, I was scratching through the leaf litter in a patch of forest near home, when I uncovered an earthworm and a slug. The earthworm was startled and dove into the soil. As it did so, it pooped on the slug. The slug just sat there. This means something, but I'm not sure what yet. Give me some time.

Oh, and this:


It's a fairly large (ca. 20mm) Anguispira alternata that I found in a sample of leaf litter. I had collected the litter sample sometime around march, and didn't process it until about June. So this little guy survived two months in a bag, sitting in my garage. Once I found it was alive, I put it in a small plastic tank with some veggies. Anguispira prefers romaine lettuce to spinach, apparently. Then I brought it back to the area where I found it. I set it down on the forest floor, and it came out to explore. I got a few snaps to remember it by.