Combining Ambient Exposure and Flash Exposure

Yesterday I was asked to take some photos at our church. The photo on the right is one of them. I used my external/portable Canon Speedlight (flash).

Seeing many people find using a flash a little daunting/scary, I thought I would share how I took this photo in the hope it might alleviate some fears some people might have.

I was standing in the church foyer which was not receiving any direct sunlight from outside. The light level in the foyer was very much less than outside. If I exposed for the Christmas tree, the background would have been very blown out and would have looked terrible. If I exposed for the background, the tree would have been very under exposed.

Whenever you take a photo with a flash gun, you have two exposures:

1. The Ambient Exposure which is just the exposure you use for any photo without a flash.

2. The Flash Exposure which is the power setting on the flash, controls how much light the flash fires off at the subject. I'm not dealing with bounce flash here.  Bounce flash has its own pros and cons.

So this is the process I used to take this photo. Using manual mode on the camera and manual mode on the speedllight.

1. Set the ambient exposure

a) Leave the speedlight turned off.  Set the shutter speed to 1/200s since that is the max sync speed I can use without turning on high speed sync on the flash which is a heavy battery drainer.

b) Set ISO to 100 since it is bright and sunny outside.

c) Spot meter the sunlit grass in the background as it is a good alternative to an 18% grey. Adjusting aperture until the arrow on the light meter in the viewfinder is centralised resulted in an aperture of F5.6

d) I took a photo (speedlight is still switched off at this stage)

e) I reviewed the image and its histogram on the camera's lcd screen. There were a couple of small "blinkies" flashing so I reduced the aperture by 1/3 of a stop.

f) I took another shot and after reviewing the shot and its histogram, there were no blinkies and I had a full tonal range on the histogram

So at this stage my ambient exposure is locked in. In the above 2 shots, the Christmas tree and area surrounding it in the foyer were significantly under exposed and dark.

2. Set the flash exposure.

a) I turned on the speedlight.

b) I started with an initial setting of maximum power (1/1).

c) I took a shot and reviewing the image on the camera's lcd screen, it was obvious the tree was greatly over exposed.

d) I dialed down the speedlight's power by 1 stop to 1/2 and took another shot.

e) Now the flash exposure was very close to how I wanted it with the tree only slightly over illuminated from what I feel was a natural look.

f) I took a couple of more photos adjusting the flash power down each time by 1/3 stop increments.

g) I eventually settled on a flash exposure 1/3 of a stop down from 1/2 at 1/2.5.

The result of the above ambient exposure combined with the above flash exposure resulted in the image on the right.

There are other techniques you can use to capture the same scene. The most obvious one would be taking multiple exposures (without using a flash) and combining them using a HDR application. But for me personally, I find HDR for this particular situation is gross overkill and too time consuming with too many variables.

The whole process from start to finish took me no more than 2-3 minutes maximum.