Q&A: The Difficulties of Recording High-Speed Video

There have been a couple of posts about film cameras losing frames when really good martial artists do their awesome. Do you know if anyone has ever used one of those extreme high speed cameras to capture one of them, then slowed it down so that you could actually see everything? Not immediately finding anything, but your search!fu is probably better than mine on this subject…

phantomjedi1

The footage exists, you find some on YouTube with a little searching. Usually, what you’re looking for is going to be labeled as, “slow motion,” or something similar. Most of this stuff doesn’t get much above 300fps, but that is more than enough to track the motions, especially when it’s slowed down so that you have the time to really watch what’s happening.

The footage isn’t extremely common because high speed video is kind of a pain to record. This is a moment when I’ll have to admit, I have not spent a lot of time with digital photography, especially on the high-end of the spectrum, so it’s possible this is easier today than it was twenty years ago with film cameras. This is going to seem like a strange tangent, but bare with me.

Taking a photo is about balancing two resources, Light, and Time. Time is measured in fractions of a second, and light is measured and managed with the lens’s aperture. Undeveloped film is extremely sensitive to light, and the entire technology behind cameras was based around that.

To capture an image, film needs to be exposed to light for a very precise amount of time. If you don’t get enough light on the film, the result will be underexposed, and too dark. If you get too much light, the image will be overexposed and blown out.

As a quick aside, some minor exposure errors can be fixed during development of the photo. This is easier with black and white film as you can salvage B&W negatives that would have been completely wrecked if you were using color film.

Now, here’s a problem. When you’re out in the world, you can’t control how much light is present. If you’re in natural daylight, or on a city street, the light that’s there can’t be removed. You might be able to add more to a specific object, but you can’t (practically) make the entire street brighter. What you can do is change how much light the camera admits to the film, OR you can adjust how long the film is exposed. An SLR camera (which used to be the standard for analog photos) allows the user to adjust the exposure length. These will range from 1/32nd of a second up to a full second, with a “hold,” or, “bulb” option that will simply expose the film until you release the shutter control.

The advantage of a shorter exposure is that it will better capture movement. If you’re trying to take a photo of a bird in flight, or a car driving down the street, you want that short exposure time. If you attempt a longer exposure, and the subject moves during that time, the result will be a blur. The film recorded the object in multiple placed and none of those points resulted in a clear image. (Also, longer exposure times are more difficult to use freehand, because any camera shake will be recorded by the entire image.)

For example, if you wanted to take a photo of a parked car in dim light, the answer would be to keep your aperture fairly small (I’ll explain why in a moment), and have a long exposure. (Possible even up to the full second, depending on how much light is available.) If it was an especially long exposure, you’d probably want to mount the camera on a tripod to stabilize it.

So, I said time and light, and I’ve been explaining how you can extend the time, but I also said you can’t change the amount of light, which isn’t entirely true. You can’t change how much light is in the environment, but you can change how much light gets onto the film by adjusting the aperture.

A camera’s aperture is, literally, how much the shutter closes down while taking a photo. The smaller the aperture the less light is admitted through it onto the film. The wider the aperture, the more light hits the film. There’s a side effect, your aperture also affects depth of field.

Depth of field is the plane in front of the camera that is in sharp focus. With a very low F-stop (so, a very open shutter), you can take photos that will put one specific point of an object into focus, while letting the rest of the world dissolve into an indistinct blur around it. This also has the advantage of being a very short exposure time, because a lot of light will be hitting the film.

A high F-Stop (so a very tight shutter) will have a large depth of field. This is ideal if you wanted to take a photo of a street, and keep as much of it in focus as possible. The weakness is that these will result in much longer exposures.

Looking back at the car example, this is why, you probably want the entire car in focus, so depending on how much light, you’d want a higher F-Stop to get the car in focus, and because it’s not going to move, you can extend the exposure to compensate.

There is one last part that affects both of these; the film itself. Not all film is created equal. Film has an ISO rating, which correlates to how light sensitive it is. The problem is, high ISO film, which requires less light, results in grainy images. So, you’re trading the speed you can take the photo at for the quality of the resulting image.

(There’s also three different kinds of color film, Daylight, Tungsten, and Fluorescent, these are color balanced for use under those light sources, and using one under a different light source will color shift the image.)

The reason I’m going through all of this is because still photography and cinematography operate off the same principles, with one key difference. A video camera has a fixed exposure length that cannot be changed because the camera has to capture the next image on schedule.

So, it used to be when you wanted to get very high speed footage, you needed to do a couple things. In addition to a specialized camera that supported the higher feed rate for the film (and shorter exposure times), you also needed to absolutely bathe the environment in light, and you needed very light sensitive film which would produce less than ideal images.

So, the high speed camera is expensive, the film you’re burning through is expensive, and the light rig is also expensive. Meaning, this isn’t cheap. You might see this employed occasion in film or advertising, but in most cases, historically TV was shot and broadcast at 30 frames per second, and film was shot at 24 frames per second. You might record at a higher rate specifically to produce a slow motion effect, but there wasn’t any point to going above this because the images couldn’t display.

So, that’s the past. Where we are now, digital cameras have become the norm, and it is much cheaper to record high speed video today than it was twenty years ago. Most modern TVs can refresh at 60fps without issue (and some support much higher refresh rates, even if broadcasting hasn’t caught up to those standards.)

Depending on your digital camera, you may be able to adjust the ISO rating on the fly depending on the sensor’s capabilities. Once you have a digital camera, you’re good to go. Hardware that would have set you back more than $10k 20 years ago, can now be replicated for less then $300.

This is a long way to say that when Bruce Lee was appearing on TV, the technology either didn’t exist yet or was prohibitively expensive. Today, it’s not that difficult to get slow motion videos of martial artists demonstrating techniques at 300fps, slowed down to something you can examine in detail. If you ramp that video back up to normal speed (by dropping frames from the playback, rather than just having an absurdly high refresh rate on your monitor), you’ll have the same experience.

A YouTube channel called The Slow Mo Guys shot high speed video (1,000fps) of the Kukkiwon Taekwondo Demo Team in 2019. High speed video is their area of expertise, and the resulting video is the most professional I was able to find on short notice.

-Starke

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