Everyone is familiar with flash – there’s probably one built into your camera or smart phone. Flash is a very versatile and useful tool for lighting your images, although it can be a little tricky to learn. I’m going to give you a brief intro into how flash works, and then talk about the predictable pros and cons of using flash. Then we’ll talk a bit about what to look for when buying one, and go into some detail about how to trigger them as this can get a bit complicated.
All flash units, whether built in to the camera, stand alone flashguns, or mains powered units, function in a similar way. They draw power (either from the mains or their batteries) into a capacitor, where it is then stored. When the flash fires, a certain chunk of this energy (depending on what power your flash is set to) is passed on to a flash tube, which creates a very brief pulse of light – the “Flash”.
That’s the real basics – clearly things get much more complex than that, and as always, if you want to know about the specifics of your particular flash, there’s no substitute for reading the manual!
I call them “flash” because that’s what they do – they “flash”. You may hear them referred to as “strobes”. That’s the American name for them. Likewise, you may hear flashguns referred to as “Speedlights”. That tends to be more of a brand name, and for people like me who’ve been around for a while, they’re still called flashguns. So now we know what they’re called, and the absolute basics of how they work, let’s look at the pros and cons.
Flash – the positives
With flash, you get lots of power in a small package. This is mainly due to the “flash” itself – the light releases it’s energy in a short pulse, rather than over a longer period of time. That makes it powerful and portable. A decent flashgun has, in the right circumstances, an output enough to balance, or even overpower bright sunlight on a sunny day – all this in a small, handheld or camera mounted package that runs off AA batteries. Something like a mains powered unit has between 5 and 6 times as much power as a flashgun. To get the equivalent amount of light from a continuous source you’d need something enormous – along the lines of what you might see on a film set. This factor alone means flash is the go to light of choice for many photographers, myself included.
It’s the same colour temperature as daylight, or close enough, so you don’t generally get issues of different colour temperatures. Flash stays cool – unless you fire off hundreds of full power flashes – so you won’t melt your subject, and you can easily attach a huge range of modifiers. That’s another plus – since flash is such an industry standard, every modifier under the sun exists for it, across every price range. You can make the light softer or harder in an almost infinite variety of ways. Flash is also very useful for action or high speed photography, as the short duration of the flash helps to freeze any movement.
Flash – the negatives
All the downsides are related to the fact that the light comes in a short pulse – the “flash” causes most of the problem. First off, it can be very hard to see what effect the light is having with such a short pulse. When you’re trying to create a certain lighting effect, it’s very useful to be able to see what each light is doing – where the shadows are being cast, how strong the shadows are, what the relative strengths of each light is – and the pulse of light from a flash is too brief for this. Bigger flash units come with a modelling light, which is a continuous light of some sort in the same housing that allows you to see how the light is falling. Some flashguns even have this ability, which they achieve by firing many short pulses of light to create a torch effect.
Another problem is that the flash of light that’s emitted has to be synchronised to the camera in some way so that it coincides with when the shutter is open. If it doesn’t, the camera simply won’t see the flash. If your flash is built into the camera, or attached to a hot shoe, then this isn’t really a problem – there’s obviously a connection between the camera and the flash, so they can talk to each other. The catch is that in order to create a wide range of lighting effects, we often want to move the flash away from the camera, and now you’ve got to find some way of triggering it remotely. There are, of course, a whole host of solutions to this, which we’ll go into more depth in a coming lecture, but for now you’ll need to appreciate that you must have some way of synchronising your flash with the camera.
Flashes, by their nature, are no use for lighting video, unless you’re just trying to create a special effect. If video is something you see yourself doing a lot of, and you think you’ll be lighting it too, then I wouldn’t invest too heavily in flash – you’ll be better off with a continuous light source, which we’ll be coming to very soon.
The last drawback to flash is that they can take a while to recycle. Think back to the beginning of this section, and you’ll recall that they work by storing up power in a capacitor, then they release it as a flash of light. If you fire a flash off at full power, you pretty much empty the capacitor, and it has to be refilled. Depending on the flash you’re using this can take several seconds. If you’re trying to capture something that’s happening in a very short space of time, then this is obviously a limitation! Of course, as you turn the power down, the recycling time drops accordingly, so you may find the way round this is to engineer a way to use your flashes at lower power outputs. All flashes will give you some idea of when they’re ready to fire again – either with a light, or an audible signal, or both