The flash unit is a Vivitar 283.
I got it on eBay.
Sensor is removed and replaced with a paper clip so that the duration of the flash is reduced to a minimum.
Maybe 0.00003 seconds or so and that will freeze a rather slow bullet.
Light is pretty dim and I usually place it 18 inches from the subject.
Rotate the head to 0°.
Pull the light sensor out of it's socket to reveal 5 holes.
The two on the right are for the sensor, short them out with a bit of wire.
Center is ground, upper left is the flash switch, connect them to fire.
Ignore the lower left hole.
On the early models there are 260 Volts in there but they don't hurt much.
You could also use the PC cord socket to trip the flash.
Alternatively you could short out the two left hand holes and use the hot shoe contacts instead.
.22 CB
The rifle is a Winchester 69A clamped in a padded vice.
This .22 rifle is about ideal for this sort of work.
Breach is wide open for easy loading with a single cartridge.
Bolt is instantly removable for safety and for bore sighting.
Longish 25 inch barrel cuts down on the muzzle blast.
Wrap paper around a pocket laser pointer, stick it in the breach in place of the bolt, and it will shine right down the bore for easy alignment of targets.
The picture shows 3 views of a CCI .22 CB cartridge. It's like a .22 Short only weaker. The 30 grain bullet was shot into water to preserve it's true shape; I use it to compare with the in-flight pictures in order to estimate the flash duration from the amount of blur. Average velocity is 680 f/s (which is rather slow for a bullet) and the standard deviation is 40 f/s (which is really bad). The large variation made sound switch timing very unpredictable.
Sound Switch
I got the plan from HiViz.com
I had some problems with the sensitivity.
When used with a .22 rifle the flash would occur early, as if the sound originated about half way down the barrel.
It seems that the sound of the air squirting out of the muzzle ahead of the bullet was enough to work the switch.
Will have to make a new one that is much less sensitive.
Doc Edgerton did not have this problem.
His famous pictures of bullets in flight were done with a .30 caliber rifle at 2700 f/s.
With his rifle set several yards back and the bullet traveling much faster than sound the first thing the sound switch hears is the shock wave from the nose of the bullet and it worked fine for him.
Here are pictures of the Front and Back.
(I have since replaced the 1,000 Ohm resister with wire.)
Wire Switch
Here is the circuit that I designed to trip the Vivitar flash when a wire is cut.
It is very simple but it works just fine.
When ready the current runs around the trigger wire and very little gets into the SCR.
After the wire is cut the current goes instead to the SCR and turns it on to fire the flash.
The SCR (Silicon Controlled Rectifier) is the main component.
When a small current runs through it's Gate the Anode conducts and trips the flash unit.
The rating must be high enough to survive the voltage in the flash unit.
The sensitivity of the gate should be fairly high so that the battery can work it easily.
I used Radio Shack part no. 276-1020 which is rated 400 Volts and 25ma gate current.
The value of the resister is chosen so that it is low enough for the SCR to function, but high enough that the battery does not run down quickly.
150 Ohms works for me.
The normally closed push button switch is for testing the circuit.
It and the connecting wires are just epoxied to the board.
Push it just before use to prove that the trigger wire is connected correctly and that the flash will really fire when the wire is cut.
A single AA cell powers the thing. Remove it when not in use unless you add a power switch.
Here are pictures of the Front and Back.
Don't knock the sloppy soldering job, it works.
In cases where the bullet is apt to deflect a little after passing through an object wrap the wire around a flat stick.
My older Vivitar (serial number 287xxxx Japan) had 260 volts in the trigger circuit; but My newer one (number 509xxxx China) has only 8 volts. Guess they redesigned it after shocking one too many customers. It is said that the old high-voltage Vivitars will fry a newfangled modern camera.
Bullet just touching a block of wood.
.22 CB at 680 f/s. ISO 400, f/6.7.
Four 7½ Watt Christmas light bulbs in a row.
Wire trigger with the wires pre cut and taped to the last bulb, just touching each other.
.22 CB at 680 f/s. ISO 400, f/6.7.
Sound trigger with it's microphone clamped right to the glass.
.22 LR at 1180 f/s. ISO 400, f/6.7.
Sound trigger at 50 inches.
.22 CB at 680 f/s. ISO 400, f/8.
Bullet cuts a fine copper wire. The wire is whacked off so fast that is left hanging in the air while the ends curl.
To prepare the wire get two feet of stranded copper wire and strip the insulation. Pick out a single strand and stretch it an inch with pliers to take out the curve. Make a wood frame and put some brass screws in it at various places and connect them to the wire switch. Just pull the wire snug and wrap the ends around the screws; nothing fancy.
.22 LR at 980 f/s. ISO 400, f/5.6.
Sound trigger at 60 inches.
.22 CB at 680 f/s. ISO 400, f/6.7.
Sound trigger at 60 inches. A laser was used to align them.
.22 CB at 680 f/s. ISO 100 Slide, f/4.7.
A bullet splashes against a steel plate.
Sound trigger clamped to the back of the plate 7 inches from the point of impact. Speed of sound in steel determines just when the flash will occur.
.22 LR at 1180 f/s. ISO 100 Slide, f/4.7.
A bullet splashes against a steel plate. Sound trigger clamped to the back of the plate just 4 inches from point of impact. Lead fragments are thin, sharp, work hardened, and imbed themselves edgewise in the nearby wooden barrier.
The concave bases of the bullets turn inside-out and just fall to the the ground.
.22 LR at 1180 f/s. ISO 100 Slide, f/4.7.
A brand new 40 Watt light bulb with the wire switch connected through it's filament.
.22 CB at 680 f/s. ISO 400 Slide, f/5.6.
A high speed bullet pulverizes the middle.
.22 CCI Stinger at 1450 f/s. ISO 400 Slide, f/5.6.
5 crayons are neatly cut in the middle. Aligned with a laser. It took several tries to get this to work; the slightest misalignment would cause the bullet to deflect enough to miss the last one.
.22 CB at 680 f/s. ISO 400 Slide, f/5.6.
These things are very cheap on the day after Christmas.
.22 CB at 680 f/s. ISO 400 Slide, f/5.6.
Test of the wire switch. Right hand twist of the rifling is apparent. The upper right inset is a stationary bullet for comparison with the blurred one. Wire strand is thicker than required for operation.
.22 CB at 680 f/s. ISO 400 Slide, f/5.6.
Two images of the same bullet. Camera is looking through the mirror down the bore and focused on the reflection of the bullet's nose. Barrel is stuck through a piece of cardboard and casts a shadow. Wire shows multiple reflections in the back-surfaced mirror. Out of focus images on the left are of the same wire and bullet seen directly.
.22 CB at 680 f/s. ISO 400 Slide, f/5.6.
Here is a Colt Government model pistol showing the initial slide movement.
Switch wire is taped to slide and wrapped across muzzle.
The 230 grain round nose jacketed bullet can just be made out in the glare of the muzzle flash; it's left hand rifling marks visible.
There is a one inch paper sticker on the slide and frame which shows that the slide has recoiled about 0.16 inches while the bullet was still inside.
The slide and it's attached parts weigh 17.5 ounces; or 7660 grains, and the bullet travels 4.4 inches.
4.4 x 230 / 7660 = 0.13 inches.
The reaction of the gunpowder accounts for the rest.
Recoil spring tention and bullet velocity are irrelevant.
.45 ACP at 700 f/s.
ISO 400 Slide, f/5.6.
(The big pistols were photographed outdoors at night in a safe place; don't you kids try this at home.)
Water balloons filled with salt water. The rubber snaps away so fast that there is a balloon shaped ball of water left hanging in the air.
Here is one the kids can do. No special equipment is required at all. The flash unit is simply wired directly to a big needle and is triggered when the circuit is completed by the salt water inside the balloon. I used the newer model Vivitar with the low voltage trigger circuit. It is probably not a good idea to use the old high voltage units while standing in a puddle of salt water.
At first I had one wire placed inside the balloon, running right through the knot, and the other on the needle.
It didn't work at all!
There was so little time delay that all I got was a picture of a sharp point making a small dent in the rubber.
I did have some success placing the balloon on a table with the wire underneath.
The flash would occur reliably just as the rip reached the bottom.
The spike is a 1/8 inch brass tube sharpened like a big hypodermic needle.
One lead is connected to the tube and the other runs right up the inside.
Strip the insulation and bend the inner wire down and back so it is hidden from the camera.
Bend it horizontal too so it is sure to touch water.
The distance from the tube's point to the bare wire controls the time delay.
Start with a 1/4 inch.
Use the emptiness of the night for a true black background, 100 yards of empty space will do.
Let the brass tube oxidize some; it looks better.
Line everything up exactly.
Use a plumb bob to locate the drop point.
Get a balloon, put in a 1/2 spoon of table salt; just pour it straight in from the salt shaker. Add the water, purge the air bubbles, tie the knot, dry the outside with a towel so no drops show. Dry the spike too.
Turn out the lights, open the shutter, and drop it on the spike from several feet.
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