Donkeypuss's Wonderful World of Technology

Hello all.

I’m writing my first post here to explain the links I’ve added to my blog—the ones on the right side of the page. I have found these links to be very useful, so I’m publishing them. Basically, they comprise my favorites list.

First, the pictorial histories of cameras. The three I’ve liked leafing through are the ones for the Hasselblad, Rolleiflex, and Nikon cameras. This guy put together a really nice site and it’s a good starting point if you’re in the market for a used camera and don’t know what you want.

At work I find myself taking lenses apart quite often. An indispensable tool for such work is the spanner wrench, which I was surprised to find is generally very expensive and crappy. Not so at US Camera, where the wrench is finally priced proportional to its cost. I remember spending more than $60 at Edmund Optics to buy one which was a clunky piece of crap. Not only that, but they sent me two left sides, so I can’t get the tips to line up. Since it arrived simply as a bag full or parts I kept thinking I just didn’t know how to put it together until I finally found a picture of it assembled at another website and realized they had messed up. By then it was too late to get a refund.

The link to build a panoramic camera is interesting. I’ve been wanting to turn an old Hasselblad A12 back into a panoramic back by rotating the camera and moving the film simultaneously at the correct speed to get the desired exposure. This is one of the links I ran into early on in the search. This guy went through a lot of trouble to build his. I’m sure mine will be worse, which is why I haven’t even started (well, there are other reasons). Haven’t looked at this link in a while, but there is a reason I bookmarked it.

During the same search period I found this guy who turned a scanner into a camera. Definitely a cool project, though he doesn’t talk much about the math behind it. Admirable that he built it with wood and scraps; I would be complaining about how expensive it is to buy the gears and get everything machined.

The mother of all sites in this respect is Professor Davidhazy’s site. He’s also built scanning and panoramic cameras out of cheapie parts. There is a lot to see at his site; the place Google originally took me is here.

My currently most active project is to replicate the flying insect photography displayed at fotoopa. This Belgian guy does some nice macro photography, but most notably is the photos of insects in flight seen here. And here he documents the early progress of the project. Really amazing!

When I first embarked on this project, I was trying to trigger a 500 EL/M electronically, and ran into this link. (Unfortunately I cannot find the 270-degree DIN connector required to make my own chord.) I measured the delay between a trigger pulse being sent in and the shutter in the lens just opening (with the camera’s mirror locked up and secondary shutter open). I did this by putting a photodiode in the camera cavity and shining a flashlight into the lens (so it measures more or less just when the shutter begins to open). This delay is a disappointing 34 milliseconds or so.

Caltech has a few free books online here. The best solid mechanics text is here. This book has examples that no other text dares to approach, and has the most complete discussion of the full Euler beam equation (used for calculating column buckling loads) I’ve ever seen.

Speaking of solid mechanics, there are some really extensive notes on advanced topics here. I ran into them while trying to do some calculations of strain on curved surfaces. Ended up not using them; they are beyond me really.

If you’re curious about the hoopla of digital photography and why pixel size matters, etc., visit this link, which is excellent with its demos of many technical aspects of digital photography. The discussion of diffraction changed the way I take pictures.

Speaking of diffraction, there is a quick calculator here.

If you’re curious about microscopes and how they work (optical ones anyway) there is a good discussion at Microscopy U. Honestly I hate biology and I’m convinced they made up the term “microscopy” to sund important—have you ever heard of “telescopy”? That’s right. In any case, the site is pretty good, but don’t expect any deep technical stuff; it’s really meant to be pretty.

This one is a gem. On this very ugly page is a lot of information of pertinent camera dimensions—such as the distance between the lens flange and the body on Nikon cameras and the thread size on Compur shutters. If you ever need to build a camera body from scratch for some reason, looking here will ensure that you design it so that the focus range of the lenses is unaffected. Unless of course you want to measure it yourself; I can verify the flange-to-film (register) distance for Nikon is correct.

Now that I’m getting into electronics I have found Discover Circuits to be very useful. Sometimes you run into articles written by frenchies that have mislabeled figures so nothing makes sense, but for the most part, it’s good. Here I learned that the “source” of a MOSFET is ground.

Back to photography for a bit… this site has a lot of exploded diagrams of various camera parts and lenses. I don’t believe in paying for manuals (I think even legally it’s worse than letting people have them for free), and, thankfully, neither do they.

I also have a project to build a digitally-synchronized mechanical clock, which is a phrase I use to feel important about my stepper-motor clock. When I first started, I knew nothing about stepper motors. I hate looking like a fool at C&H but I found this site which explains it all, more or less.

The insect photography project is requiring a source of high voltage and current to actuate the mechanical shutter. So I looked for information on camera flash circuits, which do just that. Hasn’t been too helpful yet, though I kind of know what I need now. But I ran across this site, which is an extensive discussion on flashes and strobes and has information on how to build your own. I wish the diagrams weren’t ASCII-art, but—begars can’t be choosers.

If you’re looking for the index of refraction of stuff, start here. It’s hard to find things like that on the Internet because you run into a lot of stupid middle school physics labs.

T T Lim has some incredible flow visualizations (honestly the videography could have been better, but it’s still amazing). Of note are the videos of vortex rings (smoke rings) crashing into each other. There are some rules that govern the behavior of vortex lines (axis of the vortex) that dictate the behavior after the crash. For starterts, a vortex line cannot end in free space, it must end at a surface or connect to another line, but no “T” intersections are allowed. In other words, no matter what your friends say, they cannot blow a smoke “T” or “W”—only rings. If you have a friend that can blow nice rings, try some experiments, like blowing one at the sharp edge of a ruler, with the ruler perpendicular to the path of the ring and then along the path. Try blowing one through another one, etc.

If you have a lot of data you want to fit to a curve, try zunzun. It’s faster than writing MATLAB scripts. Didn’t work for me, but that wasn’t its fault.

If you’re really into optics and are frustrated by the gap between lens design books and reality, try reading through this. They’ve documented [seemingly] everything about their 90″ telescope. I haven’t read it thoroughly, but glancing through it seemed interesting—I’m saving it for a rainy day.

This article on how to create symbolic links in Windows is the subject of my next post.

Back to astronomy for a bit… if you need a star map, go here—it computes them on the spot.

I’ve been looking for a screwdriver that fits inside a Hasselblad body, and of course, I can’t find one. But this one is hopeful, since you can stick the bits on the end of the handle. I’m going to get one.

If you’re in need of finding out what a covariant derivative is, try this. Though I ended up not using it (just like the solids notes during the strain on a shell thing) of all the descriptions I found it seemed to be the easiest to actually calculate the derivatives with. I’m glad I didn’t have to use it, though, because I still can’t figure it out.

If you’re an old DOS guy, try this on for size. BAT files still exist, and apparently are going strong. Of course you’d probably have a lot less of a headache using Python. That’s what I do to script stuff (running programs, creating specific directory trees, copying files). I used to be lazy and did stuff like that in MATLAB but that’s just dumb. Unfortunately the editor that comes with Python doesn’t have a horizontal scroll bar—probably because they want to force you to break up lines that are too long, which is easy enough to do. I found Python to be really easy to learn from scratch by yourself because the documentation is excellent. It can get a bit confusing because there are several ways to express the same thing, but drudge through it because it’s worth it.

This site goes step by step on how to write a real-time audio processing program in Windows—for example, to do FFT on an incoming signal from the microphone. Haven’t gotten around to using it, but it looks like everything is there.