Fun stuff. The nonmagnetic but conductive materials will see a changing magnetic field, or will “break” field lines, as the jargon goes, which induces eddy currents to flow and produce a field (that’s Faraday’s Law), with the induced field opposing the change (Lenz’s Law). This gives a braking effect, as you can see. Interesting that the nickel is largely unaffected by this; the composition is 75% copper and 25% nickel, while for the quarter, it is 91.67% and 8.33%.
I’ve linked to eddy current effects before, but still wanted to do my own video. I tried to narrate it while filming, but keeping everything in the frame and talking (while my hands were occupied with the demo) was too tough. I did a couple of disastrous takes and then had a fit and stormed off to my trailer, vowing to never work with myself again. I finally calmed myself down and did the silent shot, then waited impatiently for me to do the post-production.
On my recent vacation we were back at our old digs, where I had gotten the previous shots on my DLSR, and set up to use my Exilim high-speed camera (EX-FH20 model). We got a visitor within a day, and some more action over the course of the week. Mostly females, though it’s tough to say if it was just one repeatedly visiting or not, and I did spot a male, with its prominent red patch on his throat, on one or two occasions. After discovering that reaching for the camera and turning it on usually scared them away, I went for the option of mounting the camera on my Gorillapod and placing it on the table in front of me, requiring only a click to turn the camera on (it tended to shut off during the wait for a visit to the feeder). I also left it running while I stepped away, and then scanned the footage for evidence of a visit. The drawback of that option is that 5 minutes of elapsed time is more than an hour of footage at 420 fps, and almost three hours at 1000 fps. That’s a lot of data to sort through. The fixed targeting of a tripod caused some missed shots when the bird would hover about a foot away from the feeder, but the alternative was more missed shots. The difference between this and shots “in the wild” is that you know where the subject is going to be — at the feeder — and don’t have to track it as it flies. And you know it will be flying, unlike the many potential subjects who just sit there until you run out of patience and stop filming. That’s when they decide to jump or fly.
I got shots at both of the faster frame rates, along with some stills using the burst mode, which captures 40 frames in a second.
Here’s a sequence of stills from the burst mode, turned into a movie
Now we go to 420 fps
and finally, on to 1000 fps. This last movie is even better at showing the distinct change in the pitch of the wings as the bird moves away from the feeder, hovers, and then flies away. Which is pretty cool.
Note that all three movies should represent between a second or two or so of elapsed time. 420 fps = 14:1 and was 37 seconds long with some dead time at the end, and 1000 fps is 33.3:1, with a playback of 40 seconds. I slowed the frame rate of the stills down to 15 fps when I converted the sequence to a movie, to make it last longer than one second. Even so, the flap rate seems very slow for that sequence — I suppose it’s possible there’s aliasing going on, and/or my settings are different from what I thought they were. Other still sequences show more flapping. The sound they typically make jibes with what I get from the internets, that the beating is somewhere in the range of 20-200 Hz; it was this low-pitched fluttering that was my first indication that a visitor was nearby.
I did get many more shots, but uploading them to youtube is a bit of a pain — the upload generally craps out at least once, which makes me reluctant to try too many large files. I have had limited success with the java option which supposedly lets you restart a stalled upload (finally got the 420 fps movie shown here to upload; I had originally uploaded a shorter clip).
If you want to see how the pros do it, go here. Better shots, but they put in a whole lot more time and have better equipment at their disposal.
My sister had bought some of these toys for the purpose of distracting small children (with whom she works), and since I often play a small children on not-TV, I had to film it. Unfortunately I was lacking in the proper lighting equipment and it was raining, I made do with indoor lighting and my one lamp. Ergo, it’s a little dark (as far as the lighting goes. The plot is rather uplifting, I would say) though I was able to improve it a little with iMovie.
Time-lapse sunset at Lake Chautauqua, though it loses something with the youtube compression. The lake is not slanted — that was user error in setting up on a bit of a hill and not noticing that the camera wasn’t level. 12 second pause between shots, and the twilight is extended because the camera was on autoexposure, so it compensated for low light by taking longer exposures. Also used a polarizing filter to cut some of the glare, since we know that light reflected off of the lake will have a component that is linearly polarized, parallel to the water.
A year on earth is measured by one complete trip around the sun. Seems simple enough but there is a problem. The earth doesnt travel in a path around the sun that returns it to its starting point. So how do we know when the year starts or ends?
After Lockheed Aircraft completed “antiradar studies, aerodynamic structural tests, and engineering designs,” the CIA gave the green light to produce 12 aircraft on January 30th, 1960. It was called the A-11 at the time. Lockheed engineer Clarence L. Johnson was the main designer, who was responsible for the U-2. Despite Johnson’s experience, many were skeptical at first and, after months of drawings and wind-tunnel model testing, they were not convinced this beast could fly.
Out hiking/geocaching in the hot, hot sun with my camera, on the trail near South Run Park.
A number of sources indicate that for some species, female dragonflies dip their abdomens in water to deposit eggs after they’ve been fertilized; there was a bit of that going on in the stream, along with a bit of tandem flying, if you take my meaning. Not sure if the collision is territorial, a clumsy mating ritual or just Odonata dickishness.
