balancing ambient and flash ..

Use your camera in manual metering mode.
There are few things I am emphatic about in photography technique, but this is one of them. It is the best way to get consistent results with flash. In fact, make that the “only way”.

Shutter speed does not affect flash exposure. Flash exposure is affected by aperture, ISO, and camera-to-subect disctance. NOT by shutter speed. Ambient exposure is affected by aperture, ISO and shutter speed. It’s important to note that difference. The implication is that if you shoot in one of these two Auto modes (Program, Aperture Priority), then your shutter speed could vary between shots.

eg, if you are photographing someone sitting close to a window with brighter light outside, then depending on your framing, your shutter speed will vary considerably. The only way to get a consistent look between your shots, is to fix the shutter speed (and aperture) - and this you can only do in manual metering mode.

I normally use TTL flash (with the camera in manual metering), and then simply ride my flash exposure compensation up and down to get the degree of flash that I want, whether the flash is the main source of light, or merely fill.

As I mentioned on the main page ..
I tend to use the Nikon Speedlights in two specific ways :

If I am photographing outside in daylight, and I want the flash as fill-light only, I most often use Fill-Flash TTL. (With the SB-800 this would be TTL BL. With older Speedlights this is where the matrix or daylight symbol appears next to the TTL legend on the Speedlight LCD.) In most cases, it works beautifully just like this, but I still prefer to dial my exposure compensation down to around -1.3 or -1.7 stops, while still exposing properly for ambient light. The aim in doing that, is to have the flash barely perciptible in the images.

However, if I am photographing indoors where the light from my flashgun is the dominant light source, I find that Standard TTL mode is more consistent and more predictable. (This is where there is no matrix symbol next to the TTL legend on the flashgun LCD.)

In Fill-Flash TTL, the camera works according to various algorithms as it tries to figure out how “best” to balance flash with daylight. It does a pretty good job of it, but it is too unpredictable trying to second-guess an algorithm … so it is sometimes easier to just use Standard TTL mode, and if need be, dial in flash exposure compensation to bias your flash exposure up or down.

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The camera’s built-in meter will inform you only about the ambient light metering, not the flash. To check whether your flash’s exposure was correct, (ie you are working within the flashgun’s range), you will have to :
- check whether the red lightning symbol flashes after you’ve taken the photograph,
- or check beforehand with the flashgun set to Auto mode, using the test button.

You have to rely on your camera’s exposure meter in lower light in order to figure out how much ambient light will register on the image .. and how much ambient light you want to appear on the final image.

Your camera’s meter is telling you exactly what is happening .. that at the aperture and shutter speed that has been chosen, that you will have the ambient light under-exposed (or possibly over-exposed), by as much as the meter readout shows you.

Whether the camera & flash has determined the correct exposure depends on the tonality and reflectivity of the scene you are photographing. For an ‘average’ toned scene, the camera & flash will correctly expose your photo with flash light if you are within range and if flash is the main source of light.

For the best results you would want to allow some ambient light to register, and thereby not have the background too dark or even completely black. That usually looks awful. For indoors and lower light scenes outdoors, I often set my ambient light levels to about 1.5 to 2 stops under my flash exposure, so that the ambient light still registers.

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I don’t like the slow-sync option on Nikon’s cameras since it often makes the shutter speed too low and allows for too much subject and camera movement. I like having more control, and therefore I normally set my chosen shutter speed in Manual Metering mode. This shutter speed will be lower than the camera would set the shutter speed in the Program or Aperture Priority mode, but usually higher than the camera would’ve chosen for the slow-sync option.

The beauty of using digital, is that you can see the effect of your chosen shutter speed. With film, it is more hit and miss and you might have to bracket to get the best results. The actual shutter speed that I choose will depend on how much ambient light I want to have register in the image, and how much subject movement there will be, and how much ambient ’smear” I can tolerate in the image. For a specific shutter speed and aperture (with your flash as main source of light), your chosen ISO will also affect how much ambient light registers. My starting point might be around 1/15th second @ 400 ISO, using my my Speedlight in Standard TTL mode, often with some flash exposure compensation set, depending on what my camera’s histogram and LCD display tells me. If I use 800 ISO, then I might use a faster shutter speed - but it all depends. There are too many variables to really give advice on specific settings.