class="style10" Hi Speed Explosion
>Published : 27th June 2206
>Have a high speed Photosonics shoot coming up involving an explosion at night for part of a doc drama.
>I am going for 500 ASA. Has anyone out there done this before and can give me an idea about the maximum frame rate I would be able to use.
>The director wants to go 500, but I am concerned about exposure.
>Depending on which high-speed camera you have (you didn't mention whether you are shooting 16mm or 35mm), I'd suggest going at 300 or 360 frames per second, which will help with exposure.
>In post, you can slow it down even more if you need to.
>We are shooting on 16mm.
>With the Standard 16mm Actionmaster 500 your top speed is 500fps (duel perf), which will give you an exposure time of 1/1125s with the Super 16mm Actionmaster 500 you will only be able to get up to 360fps (single perf), but it will give you a 1/900s exposure time which will not have any dire effects on :
>Kodak 7218 ("You do not need to make any filter corrections or exposure adjustments for exposure times from 1/1000 to 1/10 of a second" -KODAK)
>nor Kodak 7229 ("You do not need to make any filter corrections or exposure adjustments for exposure times from 1/1000 to 1/10 of a second")
>Fuji 8692 ("No filter corrections nor exposure adjustments needed for shutter speeds of 1/1000 to 1/10 second")
>Fuji 8673 ("No filter corrections nor exposure adjustments needed for shutter speeds of 1/1000 to 1/10 second ")
>Remember with the beam splitter you are losing 4.5 stops with the Super A500 and nearly 5 stops with the Standard A500 which means you will have to be 'wide open', I would generally say err on the side of overexposure but in your circumstances I would say that is unlikely. The Cooke SK4's 9.5mm and 12mm are a great complement to the A500 with a stop of T2.
>Alternatively you could just shoot on an H/S SR3 at 150fps without losing all that stop.
>Hope this helps,
>Dean Slotar | One8Six Cape Town
>Steven Gray wrote:
class="style11">>Have a high speed Photosonics shoot coming up involving an >explosion at night for part of a doc drama.
>I am going for 500 ASA. Has anyone out there done this before and can >give me an idea about the maximum frame rate I would be able to use. >The director wants to go 500, but I am concerned about exposure.
>It depends entirely on the type of explosion you are filming. Many explosive events are "self-illuminating", that is, the explosion produces light. 500 fps is not too fast for such events, but may be too slow to capture much of the actual explosion; instead, you will be seeing the debris and dust cloud from the explosion. Ask the FX people if they have some examples of previous explosions they can show you, and if they will explain how they intend to proceed with your job.
The trick to effectively shooting an explosion is not just the frame rate for filming the explosion itself, but raising the light level of the background so that it does not go completely black at the higher frame rate.
>If you are not familiar with the type of camera you are thinking of using, you should think about getting someone who is.
>Practicing with an actual event can be a very expensive learning experience.
IA 600 DP
>There is a local sfx man that the director seems happy with, there is an assistant coming with the photosonics camera and the director wants to just see the fireball (the explosion is meant to represent a suicide bomb going off).
>I suspect that the explosion will not be that big as we are filming in Israel where the real event happened.............
>The problem with shooting a fireball explosion at night at 500 fps isn't the exposure of the explosion, which should have a lot of colour to it because it won't get overexposed -- it's the brightness of the scene before and after the explosion so that it doesn't look pitch black before the explosion goes off.
>Can you light the scene to a high enough stop so that it doesn't look too dark at 500 fps?
>It would be like trying to light a night exterior to an f/8 instead of an f/2 at 24 fps.
>David Mullen, ASC
>Steven Gray wrote:
class="style11">>There is a local sfx man that the director seems happy with, there is an >assistant coming with the photosonics camera and the director wants >to just see the fireball (the explosion is meant to represent a suicide >bomb going off).
>A couple of old fashioned flash bulbs like Press 25s added to the mix can give the illusion of a significant explosion without the bang that would normally be required.
>Smaller bulbs (AG-1s) for smaller explosions. This type of "explosion" can even be detonated indoors if compressed air is used to scatter the debris.
IA 600 DP
>Good to hear that the explosion itself shouldn't be a problem exposure wise. The main shot will not include any buildings in shot, just the explosion against the night sky, and a couple of very abstract bcu's of eye's with reflection of fireball. There is no chance that we can use big lights where we are filming in Israel, though strangely we can set off big explosions.........
>I've shot many explosions against black, effectively making them luminescence keys. It's worked really well for the job. I figured the exposure to be similar to what I shoot flames under grills on food shoots.
>Got to have those rich reds and oranges!
>Talk with the pyro person and find out what the material is that is being exploded. And ask him what other DP´s shot it at. He probably has a good idea, since he wants it to look good too.
Director of Photography
>High explosives don't really produce much flame.
There is actual footage of a suicide bombing and it's mainly an event of darkness - a magnesium-flash-bulb sized orange pulse followed by a lot of black smoke. Look at some Gulf War footage. At least the film industry seems to finally be cottoning on to the fact that shell explosions produce a big column of cascading debris and not much else (Saw "Downfall" last night).
The biggest pyrotechnic effect in modern warfare that I've seen is a tank going up but unless you're contending that your suicide bomber has a tank of diesel oil and 500 rounds of .50BMG ammunition distributed about his person I suspect the real deal would be fairly unspectacular, and more than a little gruesome.
>I assume you're going for the Hollywood-style, all cars explode into fifty-foot fireballs sort of result here.
class="style11">>I assume you're going for the Hollywood-style, all cars explode into fifty->foot fireballs sort of result here.
>Gasoline is very photo-genic.
>Gasoline is both dangerous and very fast but I will assume that you will have a pyro working on it.
>For your average explosion the fuel should be diesel mixed with a quantity of thixotrope, it burns slower and don’t vaporise. My experience is that the show wants to see the bang but spends an enormous amount of time fiddling after the gag has been set. It wouldn't be the first time I have seen a gasoline fuelled explosion being left so long that when the gag finally goes it does so real fast and with an enormous bang!!!!!!
>If you really want a slow soft explosion with fire ball, use something slow such as Hexamine or Benzoyl Peroxide. Both of these have a slowrate of decomposition and less chance of serious injury. Though I haven't used the powdered Hexamine myself (the opportunity didn't happen) I have used Benzoyl Peroxide. This stuff is great but must be handled with extreme care. Its used believe it or not for bleaching flour. It is normally transported and kept wet and before it can be used for FX it has to be dried completely. For this it should be spread on newspaper unprinted and handle with wooden spoons. It is safe enough as long as it never comes in contact with organic amines. The reaction is violent (like Chlorine and mineral oil) so always use non sparking natural materials when it is dry.
>This is a good slow bang. Add some delay's into multiple charges and the explosion could last foe several seconds. If you want serious explosions, throw in some projectile dust bombs.
>If your pyro man knows his/her job they will know the above anyway. After all it nice if a few other people know how the gag should be done.
>Well that was simple.
>Photographer, Cinematographer, Editor and, before it sent my hair grey, made me abysmal company and developing the most acrid sense of humour, a SFX tech
class="style11">> Gasoline is very photo-genic.
>Part of the reason we're addicted to oil I suspect.
>Crusher of pixels , NYC
We have a 16mm Photosonic Action Master in Israel with video assist which we use in commercials. Make sure you have the double perf film which sometimes it is hard to find in Israel.
>If you need more info you can contact me while in Israel
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