The Not So Perfect Automatic Flash Exposure A few posts back, I talked about some situations when automatic exposure will not properly work. Here, I would like to go over a very similar topic and add flash into the mix. Over time, I will be adding more posts around that, however, here I'd like to address specifically the challenges surrounding the balance between the background, or the ambient light, and the photographed subject.

(A) What you can see in the first of the 6 exposures (top left, labeled A in red) is a fully automatic exposure using a Nikon D200 with an off camera SB-600 flash unit controlled using the commander mode on the camera. While this post does directly relate to my experience with the Nikon camera system, I would not be surprised if other brands worked in a very similar fashion. If you see differences with your set up, I'd appreciate to hear back. The camera was in the Program mode, exposure compensation at 0 EV, and flash exposure compensation was also at 0 EV.

As you can see, the owl was properly exposed by the flash, however, the background behind the window was completely blown out.

(B, C) In these two versions, you can see the effect of changing the exposure compensation to - 4 EV and + 4 EV respectively. I picked these significant shifts to make it obvious what is happening, not because either of them would be right. You can see that in B, both the owl and the background are now underexposed while in C they are overexposed.

That is very important! The main, or master exposure compensation, in my case located right by the shutter button along with the mode selector, impacts both your ambient light exposure, the background in this case, and your flash exposure. In fact, if you take the photos using this setting and look into the EXIF data, you will see that the exposure compensation was propagated into the flash exposure compensation despite that showing as 0 in the camera. As a result, this does not let you tame down the background relative to your subject.

(D, E) These two frames show what you can do leaving the main exposure compensation at 0 while adjusting the flash exposure compensation. D is TTL -3 EV, E is TTL + 3 EV. Again, large values are used to make it obvious. As you can see, the ambient, or background light remains constant, and overexposed, while the owl becomes under or overexposed respectively.

(F - bottom left) is what I would recommend doing to stay sane. Switch the camera to manual mode (M) and set your exposure for the background. Set an aperture based on the depth of field you desire while maintaining a reasonable shutter speed up to the flash sync. speed, 1/250 sec. in my case. You can easily use the displayed meter in the camera to set your exposure as desired. In many cases, underexposing the background slightly highlights the subject better. In other cases, you will want to keep it one or two stops over to make it show white without blowing out the highlights. In any case, once you set this, your backgroudn will be exactly what you want it to be, flash or not.

Once you have set the background / ambient exposure, let the TTL flash do the rest. There are reasons why you might want to go to manual flash too and I will get to that later, but I believe this is a great start.

Have fun!