NB: This series of posts will convey my understanding of flash photography. While I hope it serves a useful purpose, I by no means describe this series as a be-all, end-all resource on flash photography. As ever, if you feel I have made a factual error, please correct me.
I’m normally lazy where exposing flash photos is concerned. With automatic metering methods, especially through the lens (TTL) metering, cameras can most often determine the best exposure for a given scenario. This usually my first option (i.e. where the gear I’m using allows it), as I don’t have to spend as much time playing with settings on both the flashgun and the camera. Sadly, this isn’t an option all of the time: some equipment doesn’t offer this functionality, while other times, the functionality may be defeated by extremes of lighting. In such cases, I resort to guide numbers and guesswork, or use my flash meter.
Flash meters are light meters that are able to measure the output of a flashgun. Some solely measure flash, while others can measure both flash and ambient lighting. I use a Sekonic L-358 FlashMaster, which is an environmentally sealed meter capable of flash and ambient lighting. The feature which motivated me to choose this as my flash meter was the flash-ambient ratio display, which tells me what percentage (in 10% increments) of my total exposure is coming from the flash. This is a great help, as it tells me whether I will have a bias towards flash or ambient lighting, or whether I will have both perfectly balanced.
When working in daylight, I set the appropriate sync speed for the brightest part of the frame, then place the meter in the position I want the flash to catch. In the example above (Fig. 1-3) I used a 1/125 second shutter speed, as the light was starting to fade. Fig. 2 shows the meter positioned in the absolute foreground. I placed the meter here to prevent overexposure of the foremost foliage, without heavily underexposing the more distant foliage. Had I placed the meter in the centre of the bush, the foremost foliage would have been slightly overexposed, causing it to look out of place with the background. Placing the meter here also caused a gradual reduction of light into the shadows of the bush. While the shadows are noticeably lifted from Fig. 1 to Fig. 3, they still remain noticeably darker than the rest of the foliage. Comparing the yellow flowers, the colour is more vibrant in Fig. 3 than Fig. 1, which adds some visual interest and breaks the monotony of the bush, but not at the cost of interest in the background. This leads to a flash exposure with a more natural appearance. The flash percentage of 40% corroborates this, as it indicated the picture is predominated by ambient light.
At night, I try to keep some ambient light present to preserve the mood. Using the percentage readout on the flash meter, I can usually work out a suitable compromise. Flash at nighttime is also a handy tool for preserving detail in sources of light such as street lamps and neon signs. As with daytime metering, though, placement of the meter is critical. I placed the meter in the centre of the grass area, which allowed some influence from the lamp to the right. This was to prevent it from being overexposed completely beyond any form of recovery, or to the point that it overwhelmed the building. For the more melancholic mood in Fig. 5, I metered from this position again. This led to an underexposure of the building, to give the scene a moodier appearance. A flash percentage of 30% was used, which is visible in the progressive darkening of the grass the further into the background you venture, and the slightly brighter areas at the foot of the lamp. The branches are also sharper, whilst the lamp is less dominant, and some moving rain drops have been made visible.
Unfortunately, metering isn’t a guarantee of good photos with flash. If you look at Fig. 5, you’ll notice a bright pool of light on the building doors and raindrops appearing the move in reverse. While the flash was not powerful enough to illuminate the building, it was powerful enough to be reflected off the glossy brown paint of the door. This can be avoided by placing and aiming flashguns to eliminate reflections. I will cover this in Part 3 of this series. The reversing raindrops can be corrected by changing the point at which the flash fires when using a slow shutter speed. This will be discussed in detail in Part 4 of the series. Another means of lighting a scene is to use multiple flashguns to increase range, add details that would otherwise not be lit, or even to increase differentiation between subjects in a scene. I will explore this in Part 5, when I integrate my ramblings into a series of pictures with unconscionably long captions.
In summary, while cameras are often capable of handling flash exposures for us, there are occasions where their TTL metering systems are confounded, or simply won’t suffice. Manual flash metering is the alternative and primarily helps us precisely control how much of a scene the flash is illuminating. Where available, a ratio readout between ambient light and flash helps us to achieve a desirable balance between the two light sources, whether we want a natural appearance or otherwise. Varying the placement of the flash meter allows us to alter the mood of a scene. However, beyond metering, there are other considerations when using flash, including placement of flashguns, and methods of synchronisation. Thus, a holistic approach to lighting a scene will always yield the best results possible.