Originally posted by adwb Sorry you have lost me here, if I take a image on daylight wb with a blue gell on the lens and then go to custom wb and try to make it grey I cant so how is this g fong thing supposed to work?
You don't take an image on daylight wb, you go into the custom white balance menu, put the gel in front of the lens and press the shutter while pointing at the ambient light source. That is it, it now thinks blue is neutral gray. Now when you put the same gel over your flash it will give off blue light, but your camera thinks blue is neutral gray, so whatever is lit by the flash will look normal. Everything else will have a strange color cast, since the ambient light is not blue.
Gary Fong did not invent this, people used to do this with film decades ago by using the wrong color correcting filters, we just do it digitally now.
For a K100D:
1: Press the Fn button
2: Press left to access white balance settings
3: Go down to Manual
4: Press right to adjust white balance
5: Place gel in front of lens
6: Point camera at light source
7: Press shutter
8: Now your screen should look gray, so press OK
9: Place gel in front of flash and point it at your subject
10: Shoot