BASIC INTRODUCTION TO FLASH PHOTOGRAPHY
Most digital cameras have a built in flashgun. This is an extremely handy solution for those situations when it is too dark for taking pictures. Convenient as these built in flashguns are, they do have limitations. One of these limitations is power. In the world of flashguns, power means distance and most internal flashes are only useful up to about 9-10 feet. If you want to take pictures from any further away than this using flash, you need something more powerful.
Before you can consider getting a more powerful external unit, you need to make sure that your camera has an appropriate socket. There are two types, a small round one (known as a PC socket) or, the more common, hot shoe socket. Both of these do the same job of triggering your flash but the hot shoe also holds your flash in place. The flash is synchronised with your shutter. This is why these sockets are sometimes referred to as "sync" sockets and the cable that goes between the flash and the camera is called a "sync" lead. Sync is just short for synchronised. On DSLR cameras, this synchronisation will only work up to a certain shutter speed.
The power of a flashgun is given as a "guide number" (GN for short). So, if you're choosing a flashgun for its power, this is the number you need to look for. The bigger the GN, the more powerful the flash is and the further the distance it will cover. Flashguns nowadays have their own automatic exposure system. This means that when you take a picture at less than the maximum distance, the flashgun itself will reduce its power output automatically for this reduced distance, giving you the correct exposure. If you look at a hot shoe socket from above it will either have just one contact in the centre or several metal contact points. If the latter is the case then you can use a "dedicated" flashgun. These are by far the easiest type to use. This is because they will integrate completely with your camera and work exactly the same way as your built in flash. All the flash settings you have in your camera will work on the external flashgun and all you have to remember to do is switch it on. Dedicated flashguns are mostly made by the same manufacturer as the camera but some independent flashgun makers supply units that are dedicated to specific models of camera. These are designed to work exactly the same way.
More power is not the only advantage you get from an external flash. Because the light source itself is now further away from the lens, the chance of getting red eye in your shots is greatly reduced. Also, many of the external units allow you to rotate the flash and bounce its light off the ceiling or wall. This is extremely useful because it allows you to use flash without the associated harsh shadows that are normally produced. You do need a nearby light coloured ceiling or wall to do this but it really transforms the quality of the light you get from a flashgun. If for any reason, you are not using a dedicated flashgun, then things are a little more complicated.
You will need to adjust some settings in your camera to get the best out of it. Normally, you would adjust both the aperture and the shutter speed to set the exposure. But, when you are using flash, that rule goes out the window. The flash fires so quickly that the shutter speed hardly matters. Except for the limitation mentioned earlier with DSLR cameras. To use a non-dedicated flash, you first need to find out the ISO number setting on your camera. You then need to estimate the distance to your subject. There will be a place on the flash itself to input your ISO number. If the flash has only one power output available. Then just setting the ISO number will give you the range of distances that it can cover and an aperture (f/no.). Some flashguns have a choice of power outputs. Each one will have its own distance range and its own associated f/no. Select an appropriate distance range and read off the f/no. You need to set this aperture on your camera. Go into fully manual mode and set the f/no. indicated by your flashgun. For most situations, a shutter speed of around 1/100th of a second will be fine even for Dslrs. The camera's exposure meter will probably tell you that you are going to get a badly underexposed shot. Just ignore this, your camera doesn't know that you're going to use flash. You might think that because you have to set a specific aperture that you should use aperture priority mode, but don't. If you do that your camera will probably try to set a very slow shutter speed to compensate for the dark conditions. This can give you a shot with camera shake superimposed over the flash exposure. It is worth remembering that every time you take a picture with flash, you are actually making two exposures at the same time. One is the picture you would have taken if the flash hadn't fired, the other is the exposure created purely by the flash. In the most typical situation of using flash in a dark room, the light from the flash should totally overwhelm the exposure your camera would make without it. Both exposures are defined by the ISO and aperture, but the camera's exposure is also affected by the shutter speed. If this is slow enough for the camera to have exposed the picture without flash, then you will see both images in the final result. There are times when this is exactly what you want to do. For example on a shot with a very dark foreground but a brightly lit background. You can use the flash to balance the foreground lighting with that of the background. Some cameras have a specific setting for this, called "slow-sync" or something similar. This works with their built in and dedicated guns. You can do the same thing with non-dedicated guns, but it will take some experimentation.Using "fill-in" flash: this is where the light from the flash is used just to lighten the shadows of an otherwise normally exposed outdoor shot. In this case the flash exposure needs to be much less than the camera's. Some cameras may have a fixed setting for this whilst others will allow you to adjust the flash exposure independently of the camera's. It depends on your personal taste, but traditionally, a flash exposure setting of minus 2 seems to work quite well. To do this with a non-dedicated gun involves a bit of cheating. Once you have got the "correct" aperture from the flash, you then set a smaller aperture than this (higher f/no.) on the camera and use aperture priority so the camera will still give you the correct exposure. Many people are put off using flash because of the results they see from the camera's built in flash. Which is a pity really, because flash is probably the most useful and versatile light source available to the photographer. On the surface, an external flashgun just gives you a more powerful flash, but in reality it gives you a great deal more creative control over your photographs.
Flash at Night.
1. When photographing at night, think about the background – capturing ambient light is important to create atmosphere. Slow your shutter speed down to around 1/60 sec; if in doubt, turn off the flash and take a test shot of the ambient light around you. The flash will ensure that your subject is in focus but everything else is just light trails.
2. If your camera is having trouble focusing at night, try using a torch to light up your subject – just to allow the autofocus to kick in. Turn autofocus off when you're ready to shoot, or focus manually.
3. Remember to use a tripod when shooting outside at night.
4. Try bouncing your flash – it'll give a much softer, more even light on your subjects. You can buy bounce cards for larger cameras with separate flashes, or you can make a bounce card with some gaffer tape and small, carefully placed piece of white card.
5. If your flash is too strong and you don't have a function on camera that allows you to turn it down, try adding a few layers of white tissue paper to it. This should soften it up.
6. When shooting on dull days, use flash to help brighten up your images and pick out highlights in skin tone. Flash can help on sunny days too – it'll mean you can expose the sky correctly with a fast shutter-speed and your subject's face will still be lit.
7. If you want more natural light on your subject, try using a reflector – you can make your own from an A3 piece of white card. If you'd like more definition, try holding a black piece of card near their face, just out of the frame.
8. Look for shapes in the background of your portraits – they'll help you frame your subject.
9. If you're shooting outside, try to look for an interesting location that complements your subject. Studio Lights Our Camera Club has several studio flash lamps with tripods etc, which are available to members to use at any time. There is a learning curve to find a technique that provides the results you are looking for. This includes the technical part of getting an exposure you like, and also the position of your subject / camera / lights and don't forget reflectors (these are a very fast way to change lighting effects). Why not take just one lamp home and experiment with settings and reflectors - most of our equipment can be triggered by the light from your camera's flash, so no cables and connections to worry about.