50 ohms resistor is fine here, if you want it could be even smaller.
AVR 328 tech sheet;-
Absolute Maximum Ratings:
DC Current per I/O Pin: 40.0 mA
But here is continuous DC current not pulse.
digitalWrite(CAMERA_FLASH_PIN, HIGH);
delay(100);
digitalWrite(CAMERA_FLASH_PIN, LOW);
break;
http://www.glacialwanderer.com/hobbyrobotics/?p=10
The I/O Pin is only on 100 milliseconds then wait up to few minutes. Over drive is fine here. if you do not 50 ohms but 40 ohms then change
delay(100) to delay(80).