Which sensor is fast enough for little explosions?

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Which sensor is fast enough for little explosions?

Postby thismangotballs » Sat Jun 14, 2014 5:47 am

Hi Guys... i´m planning a photoshoot with exploding food...i have a professional who is in charge with the explosions...he uses some sort of special explosive material that is mostly used in movies...which sensor is fast enough? As I´m aware that most of the sensors have a delay time...which one is fast enough?

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Re: Which sensor is fast enough for little explosions?

Postby Maurice » Sat Jun 14, 2014 9:10 am

Moved this from General forums to the Camera Axe forum.

You want to photograph exploding food so it's the food you need to capture not the actual explosive substance. This should make it much easier since I imagine exploding food is quite slow and can be captured with standard flashes. If you see too much blur you might look into airgap flashes, but try with standard flashes first.

As for the type of sensor a microphone sensor is kind of slow, but the easiest to use for this. I'd suggest trying it first. Remember to keep the microphone close to the explosion because sound travels slowly through air. If that isn't fast enough you could try either light/laser sensor to try and detect when the food moves or a pizo disc (there isn't an official CA sensor for this, but a number of people have made one on the forums). Alan sailer has done a log of explosion photos and I think he mostly uses that light sensor type I mentioned (though he made his own version). Hopefully he checks out this thread and can give a pointer to more info about what he uses.

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Re: Which sensor is fast enough for little explosions?

Postby thismangotballs » Sun Jun 15, 2014 3:22 am

Thanks Maurice! Great! Gonna give the pizo disc a try, and the acoustic one...do you thing a laser sensor which has a "lag" of about 0,5 ms is fast enough?


Do you know if there is a circuit out there to set the pizo disc on the camera axe?



Thank you
Pedro

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Re: Which sensor is fast enough for little explosions?

Postby Maurice » Sun Jun 15, 2014 4:10 am

Here is a good example of the piezo sensor on the camera axe: viewtopic.php?f=8&t=2090&p=9962&hilit=piezo#p9962

0.5 ms is a long lag for the laser/light sensor combo. I'd expect my sensor to probably be something like 100x faster than that. As a reference in that amount of time sound will travel 1-2 meters so this would be slower than the sound sensor, but it might work.

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Re: Which sensor is fast enough for little explosions?

Postby thismangotballs » Sun Jun 15, 2014 10:23 am

thanks for the piezo hint...you mean your laser Sensor in combination with the light sensor ist 100x faster...should work...could be a problem with long shutter exposures as i ´m planning to do...or is the laser invisible?....photogate sensor is to narrow for my setup....do you have any other suggestions?

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Re: Which sensor is fast enough for little explosions?

Postby Maurice » Sun Jun 15, 2014 10:29 am

You can set the laser to turn off when it is triggered, so it shouldn't show up in your photos unless the air is dirty. That said it does sometimes show up a little, but usually not. If it is a problem you could make an IR laser or light beacon and sensor, but I don't have one of those ready made in the store. It's been on my list for a long time, but I haven't done it.

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Re: Which sensor is fast enough for little explosions?

Postby alan sailer » Mon Jun 16, 2014 10:59 am

The SD5600 detector on the projectile sensor make a great starting point for what I call a debris sensor.

I decided to use this technique since I would be detecting what I wanted to photograph, the debris. Using acoustic or vibration sensors seems like a more difficult technique since the sound and vibrations of an explosion travel at different rates depending on what they are traveling through.

To get a longer baseline sensor I used a 9mm IR LED. larger LED's focus the light in a narrow beam that can be detected over longer distances. In my set-up the separation is about two feet but could be longer. The LED shines on the SD5600 detector until something interrupts the path which triggers the flash.

Maurice's points about flash speed are good. Most explosions travel at greater than the speed of sound. the debris is usually slower but not always. Stopping action at the speed of sound does require a faster than normal flash.

Cheers.

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Re: Which sensor is fast enough for little explosions?

Postby thismangotballs » Mon Jun 16, 2014 1:19 pm

Hi Alan! I really appreciate your feedback! And thanks Maurice for the kind support!

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Re: Which sensor is fast enough for little explosions?

Postby thismangotballs » Tue Jun 17, 2014 5:27 am

.....Which 9 IR mm Laser would you recommend?

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Re: Which sensor is fast enough for little explosions?

Postby Jijil » Wed Jun 18, 2014 5:09 am

wouldn't it be even simpler to get the trigger signal from the electronical ignitor of explosives? (and then apply a matching delay). The ignitor may have a low voltage output somewhere (or in the worst case, a LED glowing when started).

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