ISO is your camera's sensitivity to light as it pertains to either film or a digital sensor. A lower ISO value means less sensitivity to light, while a higher ISO means more sensitivity.
Choosing a higher ISO setting is best when the light is low or you are not able to make a long exposure. Higher ISO setting means your camera's sensor is more responsive to light, so it needs less light to reach the sensor to create a well-exposed photograph.
The "normal" range of camera ISO is about 200 to 1600. With today's digital cameras you can sometimes go as low as 50 or as high as over three million, depending upon the camera model.
What ISO setting should you use? As a general rule you want to stick to the lowest ISO possible, as this will give you the cleanest images. This is easy in good lighting conditions as your camera doesn't need a very high ISO setting in order to capture the image.
A lower ISO will produce sharper images, and the higher the ISO, the more image noise (grain) will be present. For low light photography, try setting your ISO to 800 and adjust accordingly.
For most full-frame cameras, ISO 3200 or 6400 are great for night photography. For most crop-sensor cameras, ISO 1600-3200 are great if it's a relatively new camera, or ISO 1600 if it's a much older camera.
So what is the best ISO setting for indoor photography? In general, ISO 100 or 200 can work well if you are using a tripod and you have enough brightness. If you are shooting from your hand, you have to raise your ISO to 800 or 1000.
According to this sunny day rule, if you're using ISO 100, the shutter speed should be 1/100 and the aperture should be f/16. This rule generally produces the best-exposed front-lit photos on a sunny day.
In most cases, outside in full sun, an ISO of 100 is necessary to bring about the exposure triangle. Full sun puts so much light onto the camera sensor that a low ISO and high shutter speed are required. As a result, a shutter speed of at least 1/1000 can be expected.
A low ISO value (e.g. 100 or 200) means low sensitivity to light. This is exactly what's needed in bright conditions in order to avoid overly-exposed photos. A high ISO value (e.g. 800, 1600 or higher) means a high sensitivity to light.
When more light is hitting the sensor of a digital camera at higher ISO, if the scene is not well illuminated there will still be noise in the shadows and darker areas of an image. The result is poor quality due to the noise in the image. The higher your ISO, the more grains in the image.
For that reason, ISO can help you capture images in darker environments, or be more flexible about your aperture and shutter speed settings. However, raising your ISO has consequences. A photo taken at too high of an ISO will show a lot of grain, also known as noise, and might not be usable.
Portrait photographers prefer wider apertures like f/2.8 or even f/4 — they can focus on the subject and blur the background. That's also why landscape photographers typically shoot in the f/11 to f/22 range — they want more of the landscape in focus, from the foreground to the distant horizon.
For portraits, you want the highest image quality possible. So for the ISO set it as low as you can to avoid excess noise in your photos. Go for somewhere between ISO 100 and 400.
It's easy: look through the viewfinder, center the subject, and press the shutter button, right? Next time, try skipping step two — take those few seconds to put your subject off-center, and see how much more engaging your pictures become.
If you're shooting flat subjects, the sharpest aperture is usually f/8. My lens reviews give the best apertures for each lens, but it is almost always f/8 if you need no depth of field.
Nighttime photography usually requires long shutter speeds of 10 seconds or more so you can soak as much light up from your environment as possible.
You might need to pick a shutter speed of around 1/160th, which is fast enough so that you won't get any motion blur, but slow enough to allow a good amount of light in for exposure. Shooting the night sky requires a slow shutter speed that is fast enough to avoid star trails.
Dark images happen when the shutter speed is too fast or the aperture isn't open enough. Be careful of your camera's automatic settings. Most cameras tend not to pick the right ones by default. If your camera creates an image that is too dark, use EV to bump up the brightness.
However, for most traditional portraits, it is best to use a fast shutter speed so that you can capture the moment without any blur. A typical portrait during the daytime without using flash is best taken with a shutter speed of at least 1/200th of a second handheld or 1/15th of a second on a tripod.
By far the simpler of the two popular rules for astrophotography is the 500 rule. It recommends that your shutter speed is equal to 500 ÷ Equivalent Focal Length. So, if your full-frame equivalent focal length is 20mm, the 500 rule would suggest that you use a shutter speed of 500 ÷ 20 = 25 seconds.
Rule of 500 (or 300)
When taking an untracked photo of the night sky using a camera on a tripod, this rule tells you how long you can expose before the stars begin to trail. You take the number 500 and divide by the focal length of your lens.
However, it does depend on whether you're just photographing the Moon, or whether you also want a foreground. To get a great Moon shot and little else, set your camera to ISO 100 or ISO 200 and the aperture to between f/5.6 and f/11, and adjust your shutter speed to between 1/125sec and 1/250sec.