AF Assist Light
Most entry level point & shoot digital cameras have pretty poor performance for low light focusing though they equip with AF assist lamps. It is because the lamp has a short range of reach (usually a few feet). Another fact is that it will be turned on in really dark situation only. Sometimes, we need to take pictures indoor with flash light even though the ambient light is not so low to turn the AF assist lamp on. I found that with a strong AF assist light, the focusing will be more accurate.
This project is to build an external AF assist light for shooting with flash light. The AF assist light is turned on manually and turned off automatically for 0.2 second during the picture is taken so that the light beam will not be seen on the picture.
Principle of Operation:
The AF assist light equips with an opto diode to sense the pre-flash emitted by the camera and turn off the light for 0.2 second using a monostable circuit.
Material:
An LED flash light - use 3 AAA batteries with a removable battery holder.
Electronic parts as shown in the circuit diagram - all transistors are small signal transistors. Q4 have Ic >100mA. The opto diode was salvaged from a mouse.
"How to":
1. The circuit diagram
Please note that the LEDs and the battery belong to the LED flash light.
2. Drill a small hole on the flash light for running wires.
3. Find an enclosure for the electronics and a mounting bracket for the light. Finished!
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End of the project
