So you are surprised that your flash pictures always turn out differently and unpredictably, especially when using automatic (“TTL”) flash?
Then this may help:
A. First, worry about the background, ambient light:
- First, decide “should the background light do any work?”. If you are using an automatic or semi-automatic mode, like P, Av/A or Tv/S, the camera will try to light the background well. so it will not just be the flash doing the lighting.
- Realise that there are limits to the previous: on Canon always in P mode, and on Nikon in P and A when “Slow Flash” is disabled, the camera will limit shutter speed to avoid blur.
- So if you want total predictability of the background, use manual, and set your meter to the desired ambient lighting level (I recommend you start at -2 stops, i.e. the light meter points to “-2″). See a recipe below.
In a typical room, a starting point might be 1/30th second, f/2.8, 400 ISO, and the flash pointed behind you. Auto ISO is not recommended!
B. Then, concern yourself with the flash:
- The foreground is mainly lit by flash, not by your Av/Tv/ISO settings.
- Canon cameras in particular try to avoid overexposing part of the picture, so even a small reflective object in the flash picture can result in a dark, mainly underexposed photo.
- The flash exposure metering is, on most cameras, biased toward your focus points. So the camera looks mainly where you focus.
- If you take a picture of something bright (a bride in the snow) the camera will underexpose it to give you a grey bride. If you take a picture of a dark object (a groom in a coalmine) the camera will overexpose it to give you a grey groom.
- To fix this, you can turn the flash up and down using flash exposure compensation (“Flash Exp Comp”).
- Play with the light: aim your flash at walls or ceilings if you can. and create a “virtual umbrella”.
Try it and see if you get more consistent!
Here’s a typical recent flash picture, of a nice photographer I met recently:
Doesn’t look like your usual “deer in the headlights” snap? That’s because I was following my own suggestions above. Note I also used a Honl Photo 1/2 CTO gel, to make the flash light look a bit more like the background Tungsten light. I like warm backgrounds, but I often make them a tiny bit less warm this way.