Photography Tips: Mixing Ambient and Flash

Mixing flash and ambient light results in magical results. It is not as difficult as it seems. However, it does require some understanding of a few basic principles before you get started.

I will not go into too many technicalities assuming most of you know. However, you are welcome to ask in your replies. The most overlooked component missing in other tutorials on this subject is in deciding what aperture you want to shoot with and in emphasizing that it's not just one or two things to be mindful of but several.

As we know, no single setting on your camera controls everything. It’s an interplay of balancing shutter speed, ISO, aperture, lens, distance, available light and/or flash to meet the conditions of your intended capture. The important step in mixing ambient with flash is knowing what shutter setting you need to match or approach your max sync speed (this is important) given a particular ISO and aperture. Ideally, you’ll have a meter to measure your available light let’s say for example… shutter 1/250^th at ISO 100. So your meter suggests an aperture of F8. Now you move the mode of your meter to measure flash output. The idea is to match all the settings you measured on ambient to your flash output. Now you should have shutter 1/250^th, at ISO 100 at F8 from your flash as reached by controlling your flash output. All things being equal, your image is exposed perfectly for background and foreground conditions. This may not be what you want to achieve but this is the position every photographer wants to be in. This is control central.

All Rights Reserved

On this image we wanted a slightly overexposed background with a properly exposed foreground (or at least one to our liking). This was all achieved using the technique we're describing.

This is when the magic happens. You now have control over your flash output and your ambient light. Shutter speed controls how much ambient comes into your sensor while your flash is independently controlled. As you lower your shutter speed, the ambient light gets brighter. As you shorten (quicken) your shutter speed your ambient is reduced because you are reducing the amount of time light has to strike the sensor.

This all allows you to independently control how dark or light your ambient light is while your flash exposure remains the same. A bland sky can now look dark, rich and iridescent. Blown out leaves and flowers can now be rich, crisp and saturated in vibrant hues all by controlling your shutter independently of your flash. Or you can create an awash of bright light with ambient. Your ambient can be controlled to achieve a total white or a pitch black given certain conditions all while keeping a perfectly exposed foreground. These are the controls we use to get rich deep sunsets behind a swimsuit model while she is perfectly exposed from the front.

Flash output allows you to do the same but often from the front of your subject. Keep in mind that as you increase the ambient exposure by reducing shutter speed, the highlights or potentially blown out areas will tend to de-saturate your foreground colors at some point due to overexposure whether you decide to adjust your flash output or not. Remember ambient is independently controlled now but it can have a global effect on your image capture after a point. 

Additionally, on your initial measure of ambient, make certain that this is the aperture you wish to capture your image at. Your focal plane will be affected and as such depending on your subject you may need to increase or decrease your aperture beforehand. If it’s full-length fashion or you want more in focus, you may need a broader focus field. All the rules still apply. You will still need to assess your scene as you always have and conclude that this needs to be an F8 or an F16 depending on what your goals are.