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Technically, it's a vortex, but eh, technicalities.

What I wanted to to was take some high-speed shots of an explosion, sort of like the slow motion stuff you see in the movies, except as a photo. I'm wondering if I need any special equipment to capture the air distortion around the explosion. The reason I ask is because distortion from heat ("shimmering air") can't be easily captured on a photo (at least no way that I know of), and the two instances are quite similar.

This will be shot outdoors, around noon on a partly sunny/sunny day, without any flash.

Richard Shi
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I believe that the shock-wave is strong enough to cause diffraction so that it is noticeable, but you are only going to be able to get one photo of it. You could take a composite shot using a stroboscopic flash if you were able to get it dark and the explosion itself didn't produce light.

You could use a remote trigger that is sync'ed to the detonation with a high precision delay to fire the camera at exactly the right time, but you'd also have to factor in the delay from the time the camera is instructed to capture to the time it actually captures.

If you wanted to get a series of shots, a high speed video camera is really the only option to pull it off. They are, unfortunately measured in the thousands of dollars with a $5000 one being the absolute cheapest that has a fast enough frame rate and most being in the $20,000+ range.

AJ Henderson
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Regarding the gear you need for high-speed shooting, it's true that you'll have trouble getting more than a few frames per seconds if you really want to take a photo. Or to get full HD video you'll need specific professional (thus very high cost) equipment.

But if you are willing to compromise, nowadays several cameras (usually bridges, but also even more and more point and shoot, anyway with a more reasonable price tag) offer some form of high speed video (at least 100fps). I won't give specific models but let you google or check this for example.

For video you don't really care about the trigger : you just start the recording and "explode away". But for photo, you'll also need some equipment to trigger the shot - provided the camera has some form of external trigger input. First you'd need to determine the shutter lag of the camera (how long between triggering and actual shooting) and then use some delaying circuit to first trigger the camera then trigger the explosion. Trial and error seems unadapted here, I guess you can't create so many explosions. Another way of measuring would be to shoot some fast counter (chronometer ? not fast/accurate enough ?) rigged to start at the very same time as the camera is triggered and see what time is displayed on your shot. Or you could trigger by the sound if the camera is close enough (but mind the additional delay introduced by sound velocity ~300m/s, much slower than light and your explosion)

Then regarding the optical part, I think the "shockwave" might be more visible if lighted from an angle on the side and from behind... you don't specify whether it's indoors or outdoors, with extra lighting or not, so it's difficult to say.

If you have the opportunity, a chequered (or other geometric texture) background with contrasted colors (black and white) might help enhance the visibility of the shockwave by emphasizing the distortion.

FredP
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  • The info you provided on gear is excellent, but on the optics, what makes you say that? I'd think that a frontal illumination would be better, but I'm quite a novice at this. – Richard Shi Mar 05 '14 at 09:54
  • @Shiazure I may be wrong, but I think it's similar to smoke/water vapor, lighting it from the front yields a much less valuable result than from the back. Unless you have a background as I suggested, where you need to light the background - but not the explosion, although I suppose it produces enough light itself – FredP Mar 05 '14 at 10:08
  • Ah, okay. Is there a reason for that though? With regards to smoke. Or perhaps you could point me in the direction of some reading material? – Richard Shi Mar 05 '14 at 10:31
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    @Shiazure Well, for smoke I know out of experience (candle smoke photos), but check also here : http://photo.stackexchange.com/questions/15998/how-to-photograph-smoke. The reason is probably the difference of light reflection/diffusion by smoke particles. – FredP Mar 05 '14 at 10:41
  • Thanks bunch. I'm guessing photographing water vapour is a similar concept? – Richard Shi Mar 05 '14 at 10:43
  • @Shiazure Yes only it's water molecules instead of smoke particles. When front-lighted it just gives an ugly whitish mass instead of nice-looking volutes. – FredP Mar 05 '14 at 10:49
  • The speed of most consumer cameras, even high speed, isn't going to be high enough to capture much more than a couple frames of an explosion at most. Even a relatively slow explosive shockwave moves at 1800 m/s(source). That means if the camera can shoot 100fps, the shockwave is going to move 18 meters between each frame. Even at 1000 fps, there would be 1.8 meters between each frame. – AJ Henderson Mar 05 '14 at 14:30