Andrew Davidhazy just pointed me to this kit for high-speed photography. It looks like a great way to get started for not a lot of money. The heart of the device is a microcontroller, so it has few parts and is extensible for the experimenter. It has both a sound sensor and a light sensor. The timing is not crystal-based, so it probably has only a 1% accuracy (I haven’t tested it so I don’t know this.) And it comes with a flash.

The flash is just a disposable camera that you hack into to use only the flash portion. It makes a nice, cheap way to get started. It isn’t particularly fast (1/1700 sec) and it won’t produce a lot of light. But, it will take high-speed photos of balloons popping and drops splashing (not a bullet cutting a card in half.)

For $125 it’s not a bad way to get started.

Filed under: Photography by martinw Date 3 July, 2008
No comments »

This is a question I frequently get. The short answer is, “Most likely it will.”

Most any camera will do. I use a an electronic circuit to trigger the camera, so I need one that has an electronic shutter release (most do). I use a variety of methods to create my Liquid Sculpture images, but in general, the technique is as follows:

1. Create the drop(s), somehow, knowing just when it is released, somehow.
2. Wait a specific amount of time.
3. Open the shutter.
4. Wait a bit more.
5. Trigger the flash.
6. Close the shutter.
7. Repeat ad nauseum.

I use a flash for all my lighting, and the high speed of the flash is what stops the motion. The shutter speed is not important - I usually use 1/100th second.

A person can instead use a fast shutter for some of this work, but I haven’t played with it much. Most modern cameras have a maximum shutter speed of 1/4000th or 1/8000th second. That is fast enough to stop many types of motion like single drop splashing. It won’t work very well for a popping balloon, or for the tiny droplets flying off from a splash. The fast moving parts will be blurred (which could be a desirable effect.)

One problem with using the shutter is the lag between triggering the shutter and the moment it opens - it isn’t truly deterministic. It may be 53 milliseconds on one shot and 54 on the next. That millisecond can be a large amount of time for some types of shots. My set up allows for 1/1,000,000 second accuracy, though I usually only work in 1/10,000 second increments.

Another problem is that focal plane shutters use a sliding window - a small slit moves across the film (CCD) surface. While each part of the film is exposed for only 1/8000th second, it actually takes 1/250th second for the slit to make its journey, so each part is exposed at a slightly different time. There are some clever ways to put this characteristic to use. In fact, Andrew Davidhazy at RIT has taken this to the extreme with his “strip camera”.

Filed under: Photography> Uncategorized by martinw Date 6 September, 2007
14 Comments »

I suppose it’s obvious to many that water is a special substance. To recount a few of its properties that make it so:

It has the highest surface tension of any liquid except mercury.

It has one of the highest heat capacities of all materials.

It expands (floats) when it freezes.

It is a nearly universal solvent.

For my work with water drop photography, the surface tension is the most important of these, since when the volume of water is small, surface tension is by far the strongest force at work. This force is responsible for the marvelous splashes that are possible.

For example, when a drop splashes and forms a column, the diameter of that column is largely determined by the surface tension: the higher the tension, the larger diameter of the column, all other things being equal. Put a bit of soap in the water, and the column is quite thin and tall. Also, when the column falls back down, it “falls” 5 times faster than gravity would have it fall, because it is the surface tension pulling it downwards.

The other property of water that is important in determining the shape of water drop splashes is the viscosity. Water has a fairly low viscosity, especially warm water (I have to admit that I didn’t realize how much less viscous boiling water is that cold water - about 1/6 as viscous. When I learned this it made sense why I much more often splash hot water on myself - it really is splashier.) Sometimes I add glycerin to the water I use to increase its viscosity. It makes for a smoother, slower flowing liquid.

Filed under: Photography> Uncategorized by martinw Date 28 July, 2007
9 Comments »

Here is a fascinating, old device: Lord Kelvin’s water drop static electricity generator.

Here is a physics class demonstration of it.

Do my drops suffer from this distortion? Well, I don’t have such a generator built (yet), so I don’t have just this effect going on. But, I do believe that I see the shape of drops changing in response to static charge. I need to do some more experiments with this.

Filed under: Uncategorized by martinw Date 26 May, 2007
No comments »

When people think of high-speed photography, the name that most often comes to mind is Harold “Doc” Edgerton. And rightly so, as he contributed so much to the discipline.

However, in 1876, A. M. Worthington wrote a paper entitled “A Second Paper on The Forms Assumed by Drops of Liquids falling vertically on a Horizontal Plate”; in 1908, he published a book, “A Study of Splashes,” which contained 300 photographs and drawings to supplement his narrative. He captured those images using high-speed photography. Doc was but five years old at the time.

The techniques that Worthington used were wonderfully simple:

He created a short burst of light with an open-air spark gap powered by Leyden jars (it was Doc that put inert gases and modern capacitors to work). The flash was triggered by an iron ball falling onto a pair of contacts. He timed the flash by having two identical mechanisms: one for dropping the iron ball, and one for dropping the droplet of water. By adjusting the heights of the two mechanisms, he could quite accurately determine the timing.

The dropping mechanism consisted of a spoon mounted horizontally on a pivot. It was spring-loaded and held horizontal by an electromagnet. When the electromagnet was de-energized, the spoon snapped downward, accelerating rather faster than gravity, and whatever was held in the bowl of the spoon had no place to go but down. The two electromagnets were driven by the same circuit, so they de-energized simultaneously.

He could create a drop of a predetermined size by adding as much water to the spoon as he wanted. The only tricky part was that the surface tension of the water caused the droplet to stick to the spoon. This was solved by coating the spoon’s inner surface with lamp-black – he simply held it over a candle for a bit. The powdered carbon surface supported the water without adhering to it. You can see the remnants of the soot in some of his photos.

As I consider the amount of compute power I use in my studio, I am humbled by what a clever man did a hundred and twenty years ago.

(diagram from “A Study of Splashes”, by A. M. Worthington)

Filed under: Photography> Uncategorized by martinw Date 1 May, 2007
No comments »

Note to car manufacturers: I never want a dead car battery. Never. Ever.

Call me contrary, but I don’t want my wife and kids to walk out to the rainy parking lot after a movie and find that they need to jump-start the car.

We have two cars made in the past five years. They both sport a Dead-Battery feature.

One of our cars leaves the headlights on. Really. After over 100 years of designing cars, we can still kill a battery by leaving the headlights on. Now, I know that a car can be designed to turn the headlights off when the car is turned off, even delaying for a minute so I can find my way to the front door. I know this is possible because our other car, built by the same manufacturer (and a couple of years older) does this. But someone decided that on this car, the owner wants the option of killing the battery.

Our minivan has a reading lamp for almost every seat in the car. It’s great - almost like flying on a airplane. Even my kids can turn on their own reading lights. And, they can leave them on. Once the car is shut off, the lights stay on, until the battery goes dead.

The truly diabolical part of the design is this: the van has the courtesy of turning the interior lights on when a door is opened, and leaving those lights on for a while after you exit the car. So, you can’t tell if any of the reading lights have been left on unless you stand there and wait for all the other lights to turn off.

Why do I want this feature? I can’t ever remember thinking, “Gee, if only I could only remove my keys from the car, lock it, and walk away from an empty car to have the interior lights drain the battery.”

If I don’t want my car to start, I can open the hood and remove a battery cable. Of course, that isn’t very convenient. Perhaps the manufacturer could provide a switch that will keep me from starting my car without me having to pop the hood?

Filed under: Uncategorized by martinw Date 13 January, 2007
3 Comments »

Once you try to produce a stream of drops at a steady rate, you begin to realize it isn’t as simple to do as it is to say. The temptation is to use a siphon or IV drip of some kind. The problem with these is that the amount of pressure behind the stream is dependent on the water level. As the level decreases, so does the pressure, and the rate of flow.

I ran across the solution to this a few years ago (having a degree in physics, I am ashamed to say that I didn’t know of it before). It is called the “Mariotte siphon”. It is well-known to people who do irrigation in rural areas, as a simple concrete box of this design can deliver a steady flow of water to a field. The basic diagram is:

Mariotte Siphon

Cleverly simple and quite effective. The head (pressure) is dependent on the height between the bottom of the vertical tube and the final outlet of the liquid. The level of liquid in the bottle is irrelevant. I have built one using a soda bottle, a plastic drinking straw, and epoxy.

Filed under: Photography by martinw Date 7 January, 2007
14 Comments »

Continued from previous post…

While it is a bit complicated getting the photographic equipment assembled, tested, and reliable, the true challenge is handling the liquids.

They are willfully non-linear.

It seems that everything in the world affects how they behave: viscosity, surface tension, density, temperature, the shape of the dropper, and what the cat had for dinner. Learning to control these variables is what demands the patience and creativity.

I use myriad arrangements to create the shapes: sometimes carefully placed beads of liquid on a flat surface, sometimes drops in free-fall, sometimes drops landing on a dry, flat surface, sometimes splashes of drops into a pool or with other drops, and sometimes multiple drops or splashes. And there are many things to be done with altering the physical properties of the liquids. I increase the viscosity with glycerin, and reduce the surface tension with soap. Food coloring works pretty well to add color. Aniline dyes are richer, but they affect the surface tension more than food coloring.

Propelled by the vicious cycle of serendipity and curiosity, I keep coming up with new things to try. And other people have plenty of ideas. The most intriguing so far has been the suggestion to try a high concentration of DNA in water. That would have never crossed my mind.

Filed under: Photography by martinw Date 1 January, 2007
9 Comments »

Continued from previous post…

The usual means of capturing drops is to release the drop from a dropper and use an electronic circuit to recognize when the drop is in motion, wait for a precise amount of time, and trigger the flash. The important thing is to have a reliable, repeatable method.

A photogate (”electric eye”) makes a good way of recognizing the drop’s presence. Such a mechanism involves a light source and a light-sensitive device. Common designs employ an (infrared) LED and a phototransistor, or photodiode, or cadmium-sulfide cell. HiViz.com has some designs to choose from; I have used one from the CMOS Cookbook by Don Lancaster.

The timing needs to be accurate to 1/2 millisecond (1/10 millisecond is preferred). Since an average fall time might be 1/2 second, the timing should be accurate to one part in a thousand, or 0.1%.

I have built my own timing and triggering devices (a few different ones, as I learned how to do it better.) Here is my most recent contraption:

It is overkill for anything I have needed to do, but I don’t worry about coming up short. And, I can use it for a variety of other things around the studio. It contains 10 microcontrollers programmed via USB. I created a graphical interface on a PC to configure it. It is accurate to one microsecond.

My experience is: if you want an electronics project that will take a lot of your time (unless you’re already an EE), then design and build your own. If you want to take pictures instead, purchase the equipment. Two sources are BMumford and WoodsElectronics. Both offer timing devices and various triggers. They may seem expensive, but if you value your time, they’re a bargain.

To control the camera electronically, I modified a RS-80N shutter release which I can control via a transistor. Here is the pinout for the RS-80N:

All that is needed to take a picture is to ground the shutter release pin. I added a 3/32″ stereo phono plug to the case so I can plug in my control cable when I want:

Filed under: Photography by martinw Date 31 December, 2006
17 Comments »

Continued from previous post…

I use fairly typical high-speed photography techniques:

I leave the shutter open for a relatively long time (in a darkened room) and use a flash to illuminate the splash. The flash needs to be of a fairly short duration to stop the motion well. I use something like a 50 microsecond flash. I get this by modifying the photo sensor circuit on Vivitar 285HV flash. www.hiviz.com describes the technique (as well as the theory of xenon flash units). I replaced the photo sensor with a variable 20K ohm potentiometer so I can set the duration at will. Here is a graph showing the relationship between resistance and flash duration:

This graph doesn’t tell the whole story, though. The flash does not turn on and off instantaneously. Rather, it takes a bit to start, then ramps up and ramps down. Here is what it looks like:

What would you call the duration? Typically, people measure the width of the curve at the half of its maximum power. Here, it is about 30 microseconds. Also, notice that it takes about 45 microseconds from the time the flash is fired until it reaches one half its maximum. Individual units have their own signature, too. The maximum output varies some between units, as does the shape of the curve.

It is a balancing act to get well-lit photographs. On the one hand, a short duration flash is needed to stop the motion. On the other hand, with the close focusing distance, a fairly small aperture is desired to get a good depth of field. But, that requires more light. This can be solved with careful placement of the flash and, sometimes, multiple flashes.

A bright, constant light source (photolamp) and a fast shutter speed can also be used to stop the motion. This works reasonably well if the shutter is electronic (that is, the sensor is turned on and off electronically) rather than a mechanical focal plane shutter. The main issue with a mechanical shutter is that it is difficult to get it to release at the precise moment you’d like. There is always a bit of dither: sometimes it releases 50 milliseconds after it is triggered, sometimes 60 milliseconds, sometimes 54, etc. Another problem with the focal plane shutter is that even though it may be a 1/2000th of a second or shorter, it achieves this by sliding a narrow slit across the film plane, so each part of the frame is exposed at a different time over a 1/200th of a second (which might be used to good effect, but is not generally desirable). Finally, most cameras have still relatively slow shutters: 1/4000th of a second is 250 microseconds - five times as long as what I like to use.

Filed under: Photography by martinw Date 15 December, 2006
17 Comments »