Build a disposable camera ring flash. Disposable cameras are discarded after the film has been removed. Photo labs often have boxes of them under the counter, waiting to be recycled. If you ask nicely, you can often get more than enough to experiment with. Try to get at least six for this project, all of the same type.

Step 1: Build It

Materials:
10" Cookie tin
6" Metal dog bowl (Dollar Store)
Disposable cameras
Radio Shack AA battery pack (with built in switch)
RD616 wireless flash trigger ($20 Ebay - search: "flash trigger 16 channel wireless")
Surgical tubing
Old tripod plate
Broken door cloths hanger
3.5mm phone jack
Packing Tape
Velcro
Wire
Bolts

Carl Vogt's $5 Photo Slave:
SCR 400 Volts 4 Amps (NTE5457 or Phillips C106D)
1 meg ohm 1/4 watt resistor
.05uF 400 Volt capacitor
Perf board
Solar cell from a dollar store calculator (WARNING: Dollar stores often sell calculators with fake solar cells)

Tools:
Nibbler (Radio Shack)
Punch (or nail)
Drill
File
Screwdriver
Soldering iron
Solder sucker
Wire stripper
Hot glue gun
Multimeter
Alligator clips

Step 2: Open It Up

WARNING: A fully charged capacitor can give a good shock or burn. Do not touch the circuit board or the battery holder. Use the end of the large capacitor as a handle when working on the flash. Remove the battery from the bottom of the camera. Use a small screwdriver to cut any paper sealing the camera and to pry it open.

Short out the capacitor with the tip of a screw driver by touching both leads of the capacitor at the same time. Once the capacitor is discharged, there is less risk of being shocked. WEAR SAFETY GLASSES when shorting out the capacitor. There may be sparks. Getting hot solder in the eye is a life changing experience.

Step 3: Flashes

Replace the flash trigger mechanism with wires. Use a solder sucker to remove the solder then push out the metal lever and knob with the tip of a hot soldering iron. Solder on a generous length of wire to each contact. They can be cut to size later.

There is also a simple pressure switch to turn on the flash. Push the metal prong with a nail until it is touching the board, and then solder it to both contact pads. Now the flash will always be on.

Step 4: Testing

Often some of the flashes will be damaged. Test all of them with the RD616 wireless trigger using alligator clips and mark the ones that fire reliably. Refer to the wiring diagram for the proper connections. The RD616 is used instead of directly connecting the flash to the camera and risking damage from high voltage.

Step 5: Slave

Build Carl Vogt's slave using perf board and then test it with each of the flashes. If you are lucky all three flashes will run off of one slave, otherwise you will have to build several slaves. A soldered circuit is the best, so what doesn't work with alligator clips, might work when the flashes are installed.

Step 6: Cookie Tin

Mark a 3 1/2" circle on the bottom of the metal dog bowl. Punch or drill a hole in the bowl and then use the nibbler to cut out the circle. Drill 4 bolt holes around the edge of the circle.
Place the bowl in the middle of the cookie tin. Mark all holes and drill or nibble to remove metal. Use a file to dull sharp edges.

I used an old plastic camera plate attached to a broken door cloth hanger to mount the camera, but any angle bracket will do. Drill holes and attach. Drill and install the 3.5 mm phone plug.

Cover bottom of cookie tin with several layers of clear packing tape to insulate the metal from touching the flash circuit boards.

Step 7: AA Battery Pack

Rewire the AA battery pack so the batteries are in parallel, not in series. This will keep the voltage the same (1.5 volts) but increase the amps. Use a needle nose pliers, screw driver and a soldering gun to remove metal contact plates (spring and nipples). Cut the plates with tin snips and place all the springs on one side of the battery pack, and all the nipples on the other. Take a bare wire and solder all the nipple plates together. Then solder all the spring plates together with another wire. Attach the red wire to a nibble plate and the black wire to the switch. The switch in turn connects to a spring plate. Install batteries and test the voltage with a multimeter.

Drill a hole through the lid side of the battery pack and bolt it to one side of the cookie tin. Run the battery wires through another hole into the cookie tin.

Step 8: Wiring

Solder wires from the battery clips of the most reliable flash to the external battery case. This flash will be the trigger flash. Hot glue the flash into position in cookie tin. Solder the trigger wires from the flash to the phone jack. Plug in the RD616 wireless trigger into the jack and test. Hot glue velcro to the outside of the cookie tin to hold the RD616 in place.

Hot glue the slave near the trigger flash. Solder the second flash to the slave and the battery pack and test. Do the same with the third and fourth flash.

Step 9: Finish

When everything is working, bolt on the dog dish and camera mount. Split one side of the rubber tubing and cover the edges of the inner hole to protect the camera lens. At 8 feet you should get about F5.6@60 100 ASA. The slave will not work in bright sunlight, but it's suitable for indoor use.

Modifications:
Additional modifications could be adding 4 more flashes or making a wax paper diffuser for the front of the ring. Use any leftover flashes to build a peanut butter jar strobe, a simple disposable camera slave.

Some people have built peanut butter jar slave strobes and have had trouble getting them to sync with their camera's flash. This maybe because the on camera flash is firing a distance measuring pre-flash (infrared) which is triggering the slave.

Possible solutions:
1. Set the flash to a totally manual setting, if possible, so there is no infrared pre-flash.
2. Make sure the camera's shutter speed is slow enough to sync. (60th)
3. Use an older style flash that doesn't pre-flash.
4. Construct a trigger flash with a RD616, so an on camera flash is not necessary.