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.
Flash photography has been a commonplace method for longer than I’ve been alive (22 years this August, if you’re wondering). When I started out with photography, I thought of flash as something to brighten up dark places. After a few years, though, I came to learn how powerful and versatile flash can be: filling in shadows, shaping subjects, emphasising features, changing the mood, varying the depiction of motion… For that reason, I’ve planned this series of musings out as carefully as possible. The end result will be five posts: an introduction of sorts (this post); flash exposure; placing and aiming flashguns; advanced options available on some flashguns; and to wrap it all up, a picture-laden integration post. Onwards with the introduction, I guess…
This post will cover types of flashgun, the way their output is measured and their interaction with the shutter of the camera (see an earlier post here for a discussion of shutter speed).
Flashguns come in broadly five types: in-built, hotshoe-mounted, ring, handle-mounted and studio-style. The first three tend to be mounted on the camera, while the latter two are either partially or fully separated from the camera. There are many brands available, from camera manufacturers to specialist flashgun manufacturers. Each type and brand has their merits and pitfalls, and which one you go with is purely a matter of personal preference teamed with application.
The bulk of my flashguns are Metz (handle-mount and hotshoe-mount). I’ve found them utterly reliable, nice to work with, and capable of producing some very nice lighting. For that reason, I’ve used them almost exclusively since 2006. If it’s any further recommendation, we have two fully-functioning Metz 45 handle-mount flashes that are in excess of 30 years old. Neither of them has ever been serviced. There was never any need.
Integrated flashes tend to be low powered and inflexible. However, they are handy for triggering other flashguns (this will be discussed in Part 3) and when you’re unable to carry or use an external flash. Hotshoe-mounted flashes are essentially more powerful flashes that sit atop the camera. They are slightly more flexible than integrated flashes, but the more powerful units can lead to a top-heavy camera. Just to be subversive, I normally use these flashguns with off-camera cables or remote triggers. Using them in this way is more flexible, and takes advantage of their relatively compact size.
As you may have garnered from the way I like to use hotshoe-mounted flashes, I prefer handle-mounted and studio-style flashguns. Studio-style flashes tend to be used on a lighting stand, while handle-mounts are usually left attached via a bracket. I find handle mounts are quick to switch between attached and off-camera operation, being as they are already connected by a cable rather than a hotshoe. Both handle-mount and studio-style flashguns have no adverse effect on the balance of the camera. For long shooting periods, this is crucial to preventing pain from developing, especially around the neck, back and wrists. In addition to that, both these types of flashgun provide more power.
Flashgun power is regularly quoted as a guide number (GN), which applies to a given focal length and ISO. Aperture and ISO are the critical variables for flash exposure, as the flash duration is normally very short. The guide number is calculated by multiplying the aperture by the distance. If we rearrange this, we can determine the distance for a given aperture, or the aperture for a given distance. Flash can be metered by the camera or a flash meter (I will cover this in Part 2), but understanding what’s going on is handy when it comes to solving problems in the field.
GN = aperture x distance
Aperture = GN / distance
Distance = GN / aperture
Take, for example, my Metz 76. At a 105mm focal length, it has a GN of 76 (metres) for ISO 100. So, if I wanted to know the aperture to illuminate a subject 9.5 metres away at ISO 100:
Aperture = 76 / 9.5
Aperture = 8
Compare this to my Metz 54 in the same situation. The Metz 54 has a GN of 54 at the same focal length and ISO:
Aperture = 54 / 9.5
Aperture = ~5.6
So, the flashgun with the higher GN is the more powerful flashgun. Just be aware that many manufacturers quote GN at different focal lengths: a zoom reflector can throw the light further for a longer focal length. A classic example is the Metz 45, with a GN of 45 measured at 35mm and ISO 100. The Metz 54 has a GN of 54 at 105mm and ISO 100, but only a GN of 34 at 35mm and ISO 100. On the face of things, the Metz 54 would seem the more powerful of the two, but when you delve deeper, you realise it’s only more powerful at longer focal lengths.
Another means by which flashguns are made more powerful is to illuminate the flash tube for a longer period of time. This is how the difference is achieved between full power (long duration) and partial power (shorter duration). The Metz 45, from memory, runs a slowest flash duration of 1/2000 second, while the Metz 54 and 76 tend to run a slowest duration of 1/160 of a second. This affects the sync speed able to be used.
The sync speed of a camera is the fastest shutter speed at which a flash can fully illuminate the image. That is, the is the fastest speed at which the shutter blades (or curtains) are fully opened to expose the imager. Any faster, and the flash will appear as a streak of bright light in an otherwise dark photo. Any shutter speed slower than the sync speed is also perfectly usable. Sometimes, though, the fastest sync speed of a camera cannot be used with a particular flash gun. The aperture admits the peak intensity of the flash to the imager. If the shutter closes before peak intensity is reached, the flash will have had little or no effect. This is why, with my Olympus OM-D, I tend to use flash at 1/160 of a second, as that allows for the Metz 54 of 76 to be fully effective.
In summary, flashguns are available in many types to suit many different applications. The type and brand you choose is down to personal preference and intended use. Flashgun power is compared by GN, but be careful to check the measurement conditions, as it is derived from non-standardised testing that varies by manufacturer. The sync speed of a shutter is the fastest shutter speed you can use with flash. Sometimes, you may have to run a slower shutter speed to compensate for a slower flash duration.
Oh, and if you made it this far, thank you for persevering, and I promise to have fewer words and more photos next week. 🙂