There are several rules for determining a rough guide to exposure settings in photography. The ones I know of are based on the Sunny 16 rule. It’s hard to give guidelines for exact settings, because the exposure settings you use depend on the exact lighting situation, and that can change on a second by second basis. However, these are some tips for general exposure settings. Don’t take these as gospel, use them as a starting point only, because they don’t take into account any specific lighting conditions that may be present when you take your photo.

Also, if you've read my overview on shutter speed, aperture and ISO settings ([link]), you'll know that you can change one setting and compensate by changing another setting. This applies to the general settings in here - the Sunny 16 rule says that an exposure of 1/100 of a second at f16 with ISO 100 film will give nice results, so we can increase the shutter speed by a stop to 1/250 of a second and compensate by opening the aperture to f11 to get the same exposure.

Sunny 16
In bright sun, set the aperture to f16, and set the shutter speed to the reciprocal of the film’s ISO rating. (Reciprocal means to put the number on the bottom in a fraction, with a 1 on the top. An example, 5 becomes 1/5.) So, if your film speed is ISO 100, your shutter speed becomes 1/100 of a second. If the film speed is ISO 200, your shutter speed is 1/250 (because there’s no exact match for 1/200 of a second, we go with the closest match).

Cloudy 5.6
This works the same way as the Sunny 16 rule, except that the aperture is set at f5.6 instead of f16. Once again, the shutter speed should be the reciprocal of the film speed. This also works for open shade, backlit portraits with fill flash or a reflector, indoors with indirect sunlight or stained glass windows from the inside.

Dinner for 2
Another variant on the Sunny 16 rule, but this time, with the aperture set to f2. This will give acceptable results for skylines ten minutes or so after sunset, neon signs or early morning/early evening on heavy overcast days.

Fireworks
For fireworks, try a film speed of ISO100, with a shutter speed of 8 seconds and an aperture of f8. Digital cameras are particularly good for this, because you can check your results as you take the photos and make any adjustments as needed. A tripod is essential for this type of photography, due to the very long exposure time. Also, fireworks photography is often actually several exposures that are combined together to give plenty of fireworks in the image while avoiding any light glare from a single long exposure. Use manual mode for this situation, or the camera may try to expose for a dark sky instead of fore the bright burst of the fireworks. Remember, the actual burst lasts only a second or two. If you use program, Aperture or Shutter modes on your camera, the burst will be over by the time the camera meters off it. Also, set the lens to manual focus mode and set it to focus on infinite, or you’ll lose the shot as the camera tries to focus on the brief burst of the fireworks.

Lightning
This is similar to fireworks photography, but is a bit trickier, because you aren’t just dealing with the light from the lightning bolt, but also from the cloud that is being lit by the lightning. Try a ten second exposure on ISO100 film with the aperture at f5.6. Be warned, however, that there is no guarantee when a flash will occur, so the best way to get a good shot is to take photo after photo after photo. To get the shot of lightning in my gallery (The Storm #2 [link] ) took me about half an hour and 50 shots. A tripod is essential due to the long exposure time, a remote release (either cable or infrared remote) makes it much easier, and also set the camera to manual mode and the lens to manual focus for the same reasons described in the section on fireworks. Again, check your photos and adjust your exposure as required.

Traffic Streaks
To get those cool photos of the long streaks of car lights on a busy road in the evening, try an exposure of 8 seconds at f11 for ISO 100 film. Again, a tripod is essential, although you don’t need to use manual mode, because the traffic lasts longer than the fireworks or lightning. I recommend you use shutter priority to ensure you get the long exposure required. These settings will also work for floodlit buildings, Christmas lights and candlelit close ups, although you obviously won't get the streaks.

Silky Waterfalls
To give waterfalls a soft flowing-silk look to them, you need to use a longer exposure. Set the camera to shutter priority mode, with a value of about half a second or so and then let the camera figure out the aperture. You’ll need to use a tripod due to the long exposure time. If the lighting conditions are bright, the smallest aperture may not be enough to give a proper exposure, and you could end up with an overexposed photo. If this is the case, try setting the ISO rating to a lower setting or you can use a neutral density filter or a polarising filter.

Portraits
I can’t give any exposure settings for portraits, because portraits can be taken under any lighting conditions. However, some general advice is to use Aperture priority mode and set the aperture quite wide, around f2 of f3. This will make sure the background is nicely out of focus. If you are using a compact camera that doesn’t have aperture mode, set the camera to portrait mode and this will make the camera keep the aperture as wide as possible. Also, focus on the eyes, as that is the first thing that people look at. The rest of the photo can be slightly soft, but if the eyes are sharp, it won’t matter quite as much. But if the eyes are soft, then the photo will be noticeably blurry. It’s a good idea to use the sharpening tool in Photoshop to give a click or two on each eye. If the face is filling the frame, try to place the eyes about a third of the eye down to create a pleasing balance. And finally, two notes about using flash in portraiture. First, if the flash is the main source of light, don’t use direct flash on the camera. Either bounce the flash off a wall or ceiling, or move the flash off the camera. Secondly, if you are taking portraits outdoors on a sunny day, use the flash. It’s counterintuitive to use flash when it’s so bright, I know, but the harsh sunlight can create deep shadows, particularly if the person is wearing a hat. Using the flash can fill in the shadows, so focus on the eyes, expose for the sunlit parts of the person’s face, and use the fill flash to bring detail back into the shadows.

Landscapes
In landscapes, depth of field is important, just as in portraiture, but for the opposite reason. In portraits, depth of field is used to ensure the background is out of focus to create a pleasing backdrop, but in landscapes, the depth of field needs to be as wide as possible to make sure that objects in the far distance (such as mountains) are just as clear as objects closer to the camera. Set your camera to Aperture priority, and use a narrow aperture, about f16 or f22. And use a tripod. You’ll never see a professional photographer take a landscape without a tripod. Sharpness is essential. A handy accessory is a graduated ND (Neutral density) filter. This is grey on the top, but fades down to clear at the bottom. Too often the sky is much brighter, so if you expose for the sky, the land will be under exposed, but exposing for the land gives you a pale, washed out sky. A graduated neutral density filter helps to fix the problem that is often faced when the sky and land are of different brightnesses.