How do I get shorter flash time ?

[dvdowns]

As you can see in this image I took of a light bulb being destroyed by my new invention that breaks the bulb and triggers the flash at the same time , the flash stays on for too long and movement is picked up as well . How can I get a really high speed flash that stays on for a very short time ?

[J.A.F. Doorhof]

Hi,
Use a 1/8000's shuttertime (high ISO), highspeed flash sync and a 580EX that should do the trick if you use a canon.

The problem is not the flash duration but the shutterspeed I guess.

[mikej]

The problem is the flash duration. There are some high speed strobes available, but they are expensive. I don't know what flash you used with this, but what you need is a flash that reads it's output and when it has hit the right amount of flash, shuts itself off. The Vivitar's with Thysistors will do this. A lot of people use the Vivitar 283 and 285 flashes. You have to get them close though. The closer you get them, the quicker they will shut themselves off, resulting in better stop action.

What I have done in the past is also do this in a dark room and open the shutter, run what ever it was I was trying to capture, then close the shutter. It doesn't work very well if you have to see what you are doing though.

I have to electronic kits I bought, one reacts to sound and one to an object going through the sensors.

Mike

[scoundrel1728]

Originally Posted by Mike Jordan

The problem is the flash duration. There are some high speed strobes available, but they are expensive. I don't know what flash you used with this, but what you need is a flash that reads it's output and when it has hit the right amount of flash, shuts itself off. The Vivitar's with Thysistors will do this. A lot of people use the Vivitar 283 and 285 flashes. You have to get them close though. The closer you get them, the quicker they will shut themselves off, resulting in better stop action.

Mike is describing a flash equipped with a quenching circuit and a good many of the more expensive flash units have one. It also looks like this one could have also done with a quenching circuit; the 2x4 frame for the bulb smasher is way overexposed on those surfaces where the light has hit it head-on.

I remember seeing in Scientific American many years ago an article in the column "The Amateur Scientist" about a high school student's project on the physics of shattering glass, where he had broken the fractures into four classes. In this article was a shot of a light bulb being fractured with an ordinary hammer. The student had used a collapsible aluminum foil tube formed around the hammer head to make contact with a sensor a specific amount of time before the hammer head made contact with the light bulb. You might consider putting some LED/photodiode detectors around your device's plunger to perform the same function as this aluminum foil tube to control the timing of your camera's shutter and the flash a bit more elegantly.

[dvdowns]

Thanks for all the advice guys , as you can see the contraption I set up for the first time yesterday had the flash set on manual [ mistake no. 1 ] and the head was bent upwards[mistake no. 2] so that even if the flash was on auto it could not " see" the light from its sensor . Maybe I should try a white card behind the subject , which should help to keep the glass off my workmates bench as well as reflect the flash to the sensor.I'll update as soon as I see a difference in the outcome ...

[dvdowns]

I have put up a white background and now get shorter flash times [ not short enough but an improvement ] , and cut fingers from all the broken glass ..