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.

Visualization

Continuing a thread from a while ago, here are some more pictures of fluorescing BBs and stuff:

Geological Heroes

This month's Accretionary Wedge is all about "Heroes."

I think I'll treat this as a sort of stream of consciousness post:

The first people who come to my mind when I try to think of the people who are my geology heroes would be my parents. It was they who bought me my first dinosaur book when I was about three or four years old. I was hooked ever since. My parents are both teachers - as were my grandparents. So teaching has always been a big part of how I interact with the world. This blog is just an extension of the idea of "teaching." When I was about five years old, I drew a picture of a dinosaur skull and a school bus. Above it, I wrote: "I want to be a scientist or a bus driver." Well, the bus driving thing didn't pan out - but here I am, some thirty years after the fact, researching, teaching, and sharing with the larger community all things geological.

I toyed with the idea of aerospace engineering for a while, because the Challenger disaster piqued my interest in rockets and airplanes. Then came "The Dinosaur Heresies" by Robert Bakker - I read that book cover to cover at least twice between the ages of 13 and 15. My high school earth science class also renewed my interest in geology. It was my high school biology teachers, however, that really motivated me. Mike and Sara Clough were quite the team. They were very good teachers - both in terms of pedagogical style, but also in terms of content. Evolution was not tip-toed around. It was in-your-face change in gene frequency. They gave me the basic framework of how evolution works - I still have some of those lessons in my head today. But it wasn't just evolution - it was science in general. The notion that "the nature of science" wasn't just some set methodology, but rather a rich and iterative process was something that I had "felt," but it wasn't until my time with Mr. and Ms. Clough that I really "got it." It was there I got my first taste of works by the late Stephen Jay Gould and Thomas Kuhn (yes, I read "The Nature of Scientific Revolutions" as a 10th grader: big geek, I know).

College was my introduction to the richness of geology - not just rocks and fossils, but volcanoes, and rivers, and glaciers and soils. My school had a small geology department - just three tenure-track faculty. But we took trips to Wyoming, Iowa, and all over Wisconsin. My advisor did not get tenure (it's a long story, don't get me started). I gained an appreciation for the politics of academia (to quote James Earl Jones: "watch your back, Jack"). But I'm glad to say the department survived the turmoil, and my former advisor is in a much better situation now.

Grad school was the usual milieu of fellow students, faculty and advisors. My own advisor was a student of S.J. Gould. The deeper I got into paleobiology and evolution, the more I learned to appreciate Gould's writing in small bits. His wasn't the only voice, nor the most accurate at times. There are too many names in the field to go through them all. Suffice to say they made me realize not only how to look at the rocks, but also to be very careful about acknowledging that which I did not know. Eschew interpretation, when observation will suffice. Interpretations are vital, but must be built on solid observations.

My dissertation project grew out of conversations I had with the director of the UW-Geology Museum. Again, his guidance and support has kept my trains of thought on schedule, and from derailing to often.

My wife has been a major source of inspiration. I owe her a great deal, since it was her patience and editorial eye that helped me finish my Ph.D. I find having another mind to bounce an idea off of, or pair of eyes to look at a sketch is wonderful. Especially if that mind is independent enough to look at me like I've gone bananas and bring me back to reality. I've been kicking around in the post-dissertation world for almost a year now. Since then I've had to revisit and teach a lot of physics. You don't realize how vital the works by Maxwell, Lord Kelvin, Bohr, and others are sometimes. But every single aspect of our modern society depends on the fundamental properties of gravity, electromagnetism, and the nuclear forces. That's both the technology that we use, but also the founding theories upon which fields like climatology, remote sensing, and radiometric dating are built.

So I can't name one "hero" out of everyone who influenced me over the past few decades. But they all left me with something very important. An understanding of how the world works (idealized at times, but useful) and how to apply that knowledge to pick things apart further. Although I can't leave without another salute to my mom and dad. It's probably all their fault...

Upper Flow Regimes

One of the aspects of sedimentary geology that I enjoy is the connection between sediment transport and deposition. Particularly the dynamics of the moving fluid (usually air or water) and its effects on the material being "pushed" along the base of the moving fluid.

Things like ripples in sand are a result of this dynamic relationship. I've got some more detailed posts on different kinds of bedforms, but today I want to share a video of one particularly intriguing type: antidunes.

Any bedform is going to be a byproduct of the depth and velocity of the moving fluid plus the type of material it is flowing over. For most sand, slowly flowing water will produce small ripples - you have probably seen these in the sand along the shore of a lake or river.

However, once you start trying to move fluids faster and faster over this surface, the fluid exhibits some interesting behaviors. The ratio between the velocity of the fluid to gravity and the flow's depth is referred to as the "Froude" number F_r. I've heard it pronounced "FROOD" and "FROWD." I like the sound of the former myself.

F_r = (mean velocity) / (g * depth)^1/2

For low velocities, or deep streams, this number is small (typically less than one). But, when a shallow stream is flowing very fast, it can be higher than one. When F_r < 1, it is referred to as "subcritical flow." When it is equal to 1, it is called "critical flow," and if F_r > 1, it is called "supercritical flow." Most ripples and dunes form as a result of subcritical flow. With supercritical flow, however, we start to get other bedforms, including antidunes.

Antidunes are relatively easy to create in an artificial flume. They are more difficult to see in nature:



The above video was taken by a friend of mine while in Hawaii this winter. Water was draining down the beach towards the ocean. The shallow stream started picking up speed and began to form antidunes - which appear in the flowing water as rapids that migrate upstream. Recognizing these processes in the sedimentary record requires some understanding of how they work. I'll have to spend some more time talking about sedimentary structures.

I want to thank Kelly McCullough for capturing the above video - my camera had started to act a little funny and I didn't get many good pictures. In this case, video was the right tool for the job. Kelly's a sci-fi author and all-around neat guy. You should check it out sometime.

Snails emitting light waves

I've been rather busy with teaching and a few other projects, so updates have been rather sparse and fluffy. I've been thinking about snails again (a reprieve from boring my wife with tales of wave functions and magnetic flux equations). Last year, quite by accident, I discovered that the shells of many of my snails fluoresce a dull orange under long-wave ultraviolet light.



The image above is of a set of Oreohelix sp. shells that I had collected a couple years ago. This is part of a rather large collection of a few thousand shells that I've amassed. I suspect they will lead to some additional posts and manuscripts in the next few years. One long-term study will be to investigate why these shells fluoresce a bright orange along parts of their shells, dull blue elsewhere, and on the inside emit this pale blue-green color. I've seen shells fluoresce in parts, and not others, but I have not observed the stark contrast in fluorescent regions before. I suspect it has something to do with the organic molecules bound with the calcium carbonate, but what the "activator" is, I have little idea. Some sources suggest that divalent Manganese causes an orange or red color, although how a snail could decide to use Manganese in one part of the shell and not the other. Nor have I found much in the literature that would suggest some cause of the light blue-green. My thoughts regarding the proteins as the culprit stems from the lack of strong banding on some of the more bleached shells.

For those of you that are not familiar with the term, fluorescence is the property some compounds possess whereby they absorb UV light. The UV light energy (wavelengths too small to be detected with our eyes) excites electrons in the outer orbitals of some "activator" atoms, causing them to jump to a higher energy level. As the electrons fall back to a lower energy state, they emit light energy at longer, visible wavelengths. A small bit energy is dissipated as heat, but the rest is emitted as visible light. Day-glo highlighters, blaze orange safety materials, and even laundry detergents contain fluorescing compounds (so the clothing emits more visible light and appears "brighter" when they come out of the wash). Even scorpions will fluoresce.

Easter Trilobites

I went fossil-hunting today, and picked up some trilobites. I promptly handed some of them out to friends and family. I think they make a much better gift tradition than chocolate bunnies and jelly-beans.