Flash Photography and Low-light Flash
Many people end up hating their flash—especially if it's a pop-up unit or a hot shoe-mounted gun—after using it indoors. The flash can overpower the ambient light to give horrible harsh lighting with nasty, dark shadows. It gives no modelling for three-dimensionality and totally kills the atmosphere, and finally, there's the age-old problem of red-eye. As when using a flash outdoors on a bright day, the key in low light—either indoors or outdoors—is to balance the flash with the ambient light, both in intensity and color. The flash can act like the main light source, with the ambient light acting as fill light to retain the atmosphere and fill in any shadows, or the ambient light can be the main light, with the flash just picking out a detail of the scene. Alternatively, you can carefully blend the two so that the flash does very little apart from seamlessly adding to the mix and lifting the brightness of the scene to a higher level. Many photographers stay away from using flash, as they are unsure of the settings and how best to attain a true image, it’s so important to understand light and the use of flash especially when recording someone’s wedding as the official photographer. You will need to take into account the color temperature of the lights present, as there are several different types of indoor lighting, all of which cast different colors. Some common light you will likely find yourself working with includes cool, blue light coming in through windows, green/ magenta light from fluorescent tube lights, orange from tungsten lights, and a very warm orange from candles and the like. If you then mix in a flash that's balanced to slightly cooler than daylight you can have an interesting mix. Sometimes a burst of natural-looking flash light can give a great splash of light and help make the subject pop out of the photo, this photograph of my Daughter was taken with my fuji x100s and the inbuilt flash, I had to ensure I was close enough as its not very powerful but the added flash lifted the shot for me.
If you are taking a photo inside its vital that you keep skin tones correct, while the rest of the room is bathed in warm ambient light. Other times you may wish to gel your flash so it's the same color as the dominant ambient light and blends in seamlessly. You can also gel your flash so it's not fully matched, but is some way there, such as using a half CTO gel in a room full of tungsten lights, for example. There really isn't any one-size-fits-all method, just trial and error to see what works and what doesn't. Whatever the color, it's the ambient light intensity that's crucial. Just as if you were outdoors, take a reading for ambient light and set your camera to that, then experiment with underexposing. The biggest difference will be the light levels, so you may have to drop to slow shutter, this photograph taken at a lovely wedding here in Somerset was taken with manual camera settings and of course manual flash.
If the light is very low then get your speed settings, wide apertures, or high ISOs to get an acceptable background exposure. For ultimate quality, keep your ISO as low as possible whenever you can. This often means shutter speeds are low and necessitates the use of the tripod. You will also need a subject willing to keep reasonably still to avoid a ghost image showing where they have moved. Toward this end, it's often good to give them something to lean on as it aids in keeping them still. Now you should introduce your flash, and increase or decrease its power so it gives the correct exposure on the subject. Just like working outdoors, a larger light source gives a softer light, but be aware that it's easy for the flash to overpower the scene and become the dominant light source, especially if you're using modifiers like umbrellas, with their scatter-gun approach. Softboxes or lights fitted with grids can be better used to put small pools of light where you require them, and nowhere else. Its not the best option for a fast paced wedding but if you have the time and used this way, they can often replicate the look of a spotlight highlighting just part of the scene, and of course, a larger-size fill light can be used to raise the ambient light level. A light can also be bounced off the ceiling to provide fill light. If that light is gelled to match the ambient light, it can be quite subtle, too.
Get that flash out and practice, its really not as scary as you may think.