Deconstructing light, part three: balancing ambient

One of the neat things you can do when you’re controlling the light is highlighting your subject, but preserving the ambient atmosphere. Today’s post focuses on how to do that.

Ambient light is your friend: it helps you to fill in the background with pre-lit object, providing compositional context; but more importantly, you can use it to preserve the atmosphere of the scene, which can be difficult to recreate if you’re using 100% flash or strobe only. All of the previous control points for single and multiple lights apply, of course. The two major challenges with balancing ambient are exposure and color. I’ll deal with exposure first.

There’s no fixed rule for this, but the more ambient you want to preserve, the closer your exposure must be to ambient exposure; the best way to do this is by shooting in manual mode and balancing out your shutter speed and aperture until you’re around one stop underexposed; I wouldn’t do anything more than three stops of difference (unless you have very bright ambient point sources) because very little, if any, ambient sources will remain. You’ve got three parameters to play with here – shutter speed, aperture and ISO. Shutter speed should fall somewhere between your max sync speed and around 1/30s if you’re dealing with people; higher if there are moving objects, lower if static. Aperture should allow you to hold in focus whatever you need to. ISO is the remaining balancing factor once you have set the other two – try and keep this low to maintain image quality, however. I generally don’t go higher than 800. Note that flash power should be the last thing that’s altered (and done by the camera’s meter to balance out the required exposure) – this is because you are firstly setting your exposure based on ambient, then filling the primary subject with the precise amount of flash required for a proper exposure.

Color is actually simpler: if it’s daylight, or close to it, there’s no need to gel your flashes, because they operate at fairly close to daylight Kelvin temperatures. If it’s tungsten or fluorescent, you’ll need to use the correct gels over the front of the flash so they provide the same temperature color source as the ambient lighting; you’ll also then have to set the white balance in-camera to match ambient. Note that you don’t always have to match the flashes to ambient; sometimes having a bit of temperature difference isn’t a bad thing, as it can help to highlight the subject. Just don’t make the difference too glaringly obvious.

Let’s move on to the examples.

Omega Speedmaster 9300. Nikon D800E

One of the more common situations I face where I have to balance flash and ambient are lume shots of watches – you need a very long exposure to capture the glow luminous material; often 30s at f16 ISO 100, or longer. However, a luminous dial pattern on its own isn’t very interesting, so I usually supplement this with some ambient. You could do this two ways – composite a regular (but underexposed by several stops) shot in, or just add a manual flash kicker to define the case. Here, I used 1/16th power from top left through the diffuser box.

Sandwich. Nikon D700

The background glow is the restaurant decor; I had flashes reflecting off umbrellas left and right to illuminate the sandwich. Exposure was balanced out to expose two stops under ambient for the restaurant, with a longer exposure time and base ISO (sandwiches don’t do much moving).

Autumn texture. Nikon D90

One flash from the left, not diffused to provide a bit of harsh light to add texture and definition to the subject; exposure 1/2 stop under ambient. I wanted to fill the shadows and create some cross-lighting effects rather than make things soft and diffuse; a very flat angle for the flash position was used to accomplish this.

MRI room. Some of you might recognize this from a previous on assignment post. Nikon D800E

The objective of this shoot was to show the clean, high-tech environment of the hospital’s new MRI machine. The MRI and room itself had ambient lighting on both the machine and ceiling; if we shot with this alone, firstly our models wouldn’t have been able to keep still for long enough, and secondly, the ambient light was far too cool with a large difference in color temperature to the machine. Hence, flashes were used to illuminate the room and models – one in a reflective umbrella to the top right corner of the room; I needed throw and definition for the whites. The second one was placed on top of the rear casing of the MRI to fill the back of the room.

Mammogram. Nikon D800E

Here, the client wanted to convey a warm, friendly feeling to the room; nothing says this better than warm lighting. The color temperature of the flashes were shifted with gels; the primary source source was a flash reflected off an umbrella behind and above the machine; a secondary flash was bounced off the wall behind me (and to the right of the patient) to provide fill at 1.5 stops under the main flash.

Sony RX100 product shot. Nikon D700

The final example is one of those deceptively complex shots: one flash from top right was fired through the diffuser to light the camera body and background, but the exposure was altered until it balanced out that of the screen. If I’d just used the native sync speed of 1/250s and stopped down, the screen would black out because it isn’t that bright.

Come back again tomorrow for the final part in this series! MT

A primer on lighting equipment is here. Part one on single sources can be found here; part two on multiple sources, here.

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