Martin Waugh

I often get requests for information about techniques. Here is the “stock reply” that I have been using to save me some time. Now I can just point people to this post!

Equipment

I don’t use special cameras or lenses, really. I am currently using a Canon 5D and a 180mm macro lens, but other equipment works, too.

High-Speed Tricks

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. “Speedlite” flashes (as opposed to studio strobes), control the amount light output by varying the flash duration. Not surprisingly, the shorter the duration, the less light (many studio strobes are the opposite!). So, you can get a short duration by setting the flash for low power (1/16 or 1/64). I get this by modifying the photo sensor circuit on Vivitar 285HV flash (a bit more detail) .

Timing the flash is done with a photogate and electronic timer. www.hiviz.com has techniques, equipment diagrams, and kits.

I have built my own timing and triggering devices (a few different ones, as I learned how to do it better.) My advice 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. Here are some vendor choices: www.bmumford.com, www.woodselec.com, www.universaltimer.com, and www.cognisys-inc.com. And Make magazine has a kit: www.makezine.com/flashkit and www.quaketronics.com/flashkit.

The Light

It’s hard to give a single formula for lighting, since different situations lend themselves to different approaches, however, using an on-camera flash is not an arrangement that I prefer, especially for the clear liquids. Rather, I use remote flashes in various locations. In the end, lighting these shots is no different from any other similar material. The only difference is that I use a flash with a short duration to stop the motion. So, for clear liquids I use the same techniques as I would for glass, since they behave optically much the same. For an opaque liquid, like milk, I light it as I would for a white bowl (except smaller, of course.) A good book on lighting is “Light: Science and Magic”.

You will wrestle with depth of field issues. There are a few things you can do to help, but they all have their downsides.

The Liquids

The photography is in many ways the easier part of what I do. Handling the fluids is what takes the creativity and patience.

I have developed a fairly complex system of computer programs and hardware and mechanics that I use to create drops and do the timing. Still, I take a lot pictures and make a lot of mistakes. I have a post that goes into more detail on this, too.

Other resources

A simple setup is described in www.dpchallenge.com.

www.photosig.com

PopPhoto

North Carolina School of Science and Mathematics

Andrew Davidhazy, at the Rochester Institute of Technology, has good information on high-speed techniques, as well as other fascinating types of photography.

Fotoopa.com has some creative techniques.

Harold “Doc” Edgerton, of course, is the father of the xenon flash tube and high-speed photography. Search for his books on Amazon.com.

I realize that I haven’t written about my trip to Boston.

Last August, I was invited out to Boston to help on the set of Discovery Channel’s show, “Time Warp”. It was an opportunity to finally get some high-speed video of the kind of drop-on-a-splash collisions that I have been photographing for years, but have never seen in video. I jumped at it and I am very glad I did.

The crew was very hospitable, good humored, and accommodating. The host, Jeff Lieberman, and I share a number of interests, so we had a lot to talk about beyond the immediate task at hand. Jeff also told me that usually the segments are fairly tightly scripted, but in this case he convinced the director to just let us play while they filmed us. And, play we did.

We were on set for 10 hours, and then Jeff and I played for five more hours. There was a lot of footage that ended up on the cutting room floor, so to speak. What was most educational for me was seeing the relative speeds of the different stages of the collision. I had some sense of the variation, but seeing the complete collisions from start to end was still informative.

Shooting video is a bit different mindset than shooting stills since timing is not much of a issue. A lot of my electronic equipment was not necessary. The cameras we used were capturing at 10,000 fps w/HD quality, and would keep the most recent 2 seconds of data. So, I could fiddle around and when I saw something I liked, I just said “Stop”, and we had the last 2 seconds to cut from. Of course, it isn’t a dozen megapixels per frame.

The issue that is common between shooting video and stills is insufficient light. We were shooting at f/5.6 mostly, and even at that, we should have had more light. And, I wanted to be shooting at f/11 or f/16. For a back light, we used a bank of seven bulbs in a honeycomb pattern; each was 1500 watts, I believe. And we had a 7kW spotlight above. After a short while, the water was steaming and we were sweating. I hate to think what it would be like with enough hot lights to get another 2-4 stops of exposure.

All in all, I got everything I wanted out of the trip, and the resulting clip has been good to have around. It can be seen on YouTube.

Every now and then I get a question about managing depth of field in drop photographs. Indeed, it can be a bit frustrating.

Depth of field is a perennial problem with macro photography. It’s just the physics of it. The depth of field is shallower with higher magnification, so it makes little difference which lens you use, as long as you still magnify the same amount (I have a Java-based depth of field simulator where you can play around with these variables.)

There are three things you can do to get more depth of field; they all have their trade-offs:

Use a smaller aperture – this requires more light and hazards loss of sharpness due to diffraction

Back up some and crop – you will have a better depth of field, at the expense of resolution.

Choose a camera with a smaller sensor – unfortunately, these usually have fewer pixels than a larger sensor, so again, you lose resolution, and they often don’t have as good of noise immunity.

It is often said (in fact, I just said it myself) that it makes no difference which lens you use as long as you use the same magnification. Well, this is a bit misleading. The mathematics are the same, but the visual effect is noticeably different. With a short lens, the background is not magnified as much as it is with a long lens, so it appears to be in better focus.

Having said all this, I often have to very carefully set my focus point (I use a macro slider to move the camera a bit closer or farther). It always seems to be a delicate balance.

On the other hand, a little bit of blurring toward the back does help give a sense of depth and even intimacy.

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.