If you show up on a shoot or have a spontaneous need to roll tape with no light kit: relax. Today's cameras and their ever improving contrast ratios and light sensitive electronics are very forgiving. However, if you're not so lucky to have the ideal situation in which to make use of the sensitive electronics, here are some tips to help you get that shot and look like a pro.
Available Light Indoors
Indoor lighting scenarios are innumerable, but, for the most part, you will be dealing with sunlight and incandescent mixed sources in the day.
The first tip is a no-brainer: don't place your subject in front of a bright window. Move the subject to a place where the light source (window) falls on the front. If that is impossible, frame the shot tighter so most of the window is not visible.
In most cases. the auto iris of the camera will adjust as you remove the light source so exposure will not give you an undesirable backlight or silhouette effect. Turn on as many lights as possible to offset the stronger sunlight behind the subject. Use the manual aperture setting to counteract the camera's desire to overcompensate. In situations where you have a choice to use sunlight or incandescent, use the former. Sunlight is more colorful than the house lights. Remember to white balance for the dominant light source and, if the light varies a lot in the shot, write down the f-stop for the lightest and darkest spots in the shot and then, using the manual setting, place your final f-stop in between the two readings. When all else fails, use the backlight button, but be proactive. Make the light work for you. Don't let the light make you work.
At night with incandescent light sources you'll have more freedom to move both the subject and the light. Again, it's a good idea to keep the light source out of the frame. but this time you don't have to compromise framing, just move the light. Another reason to remove the light from the frame is because table and floor lamps (practicles) sometimes leave a halo around the subject when placed in the frame. The light falling on the subject should be the brightest spot in the frame, with as few deep shadows 2.5 possible. Try to mold the light across from one side of the subject to the other so the difference between lighter and darker helps create the illusion of three dimensions.
Available Light Outdoors: Nighttime
We've all come across the difficulties of lighting outdoors at night. If all you have is the porch light, try to bounce the light or at least remove the light source from the frame. Don't place the subject directly below the light, this will cause harsh shadows under the eyes, nose and chin. Headlights from a car can work but they are hard and will act like spots: try bouncing them also to diffuse the light. I've seen flashlights bounced off clothing work, but this is really tricky. Moonlight is unlikely to work well, no matter how bright it looks to your eyes. In any event, move your auto focus and aperture to manual. At such low light levels, the auto sensors do not work well.
Available Light Outdoors: Daytime
A sunny day is okay, but overcast is a better situation. An overcast sky throws diffused light, creates very little shadow and you can shoot all day. If there is full sun, your subject may cast deep shadow since sunlight is very hard. The stronger and higher the sun, the deeper and more contrast the shadows, so there's not much opportunity to create 3D molding. Try to avoid shooting from 11:00am to 2:00pm. During this time, the sun is high and creates overhead lighting, which is very flat. In this situation put your subject under a tree in the shade, but don't show too much of the sky as background, since the dappled light under a tree will contrast strongly with the full sunlight in the background. Keep the camera angle higher so you can avoid too much bright sky or a hot background. Sunlight provides plenty of light for a reflector, however. Position your subject in the shade and then use a reflector to bounce sunlight onto your subject. This is really an ideal situation.
If you have to deal with varying light intensities, because the subject is moving, for example, set the aperture to manual, take a reading of the brightest and darkest areas and then set your f-stop or aperture in between the tv.rG. If full sunlight with a beach or snowscape setting is unavoidable, at least position your subject with the sun to the side so she doesn't have to squint directly into the sun. If available, you can bounce light from the sun with a white sheet, poster board or foam core. You don't need a big piece, just enough to illuminate the face. The upshot is to avoid sharp shadows and great contrast. Some shadow is good on people, because it results in a stronger three-dimensional look. In shooting inanimate objects, less shadow is desirable because you want to see all the detail that shadows may hide.
If the light is too hot, your camera may overexpose the shot or overcompensate in the auto mode. What you really need is a neutral density filter, even a cheap one. These gray filters don't change the quality of the light, just the intensity. They screw on to the front of your lens and come in two-stop increments. Also, if you want to shoot sky and create fuller and deeper looking images, try a polarizer, it acts like an ND filter but changes the quality of the light much like polarizing sunglasses.
Most of the time, you will have at least some control over your lighting. It's all in how you apply your creativity to solve the problem that will allow you to get the best exposure. These tips will help but you can come up with your own problem-solving ideas if you are thoughtfully patient.
One time, I shot a wedding in which I had only candlelight, and very little of that during a portion of the reception. The host would not let me use my camera light. I told him I could not get a good exposure with such limited light. He shrugged his shoulders. I knew the client would be asking later why the interviews were so dark. I thought of how I could exploit the situation to solve this problem. If I could not bring light to the subjects, then I would bring the subjects to the light. I gathered as many candles as possible, put them on a single table, and then brought subjects to the table to conduct the interviews. The final results were actually better, more natural and lovelier than if I had whipped out my artificial light kit.