Learn about ISO and White Balance in photography
In the old days, one of the first decisions you made when buying film was the ISO or ASA rating. One would purchase a film for daylight use at a rating of 100 or lower light conditions at about 400. The rating stood for the film's sensitivity to light. A higher number meant the film was "faster" and you could use it to shoot in lower light conditions.
ISO comes from the International Organization for Standardization, the group that develops this and other standards for various uses. The letters ISO are not an exact acronym and is what they chose as a short form of their name. Like with typical shutter speeds and F-stops, the typical ISO values are used to half or double the amount of light. So an ISO setting of 200 means the sensor is twice as sensitive to light as ISO 100.
Practically, a lower ISO is useful for shooting in lower light conditions. One of the differences between lower and higher end cameras is in their ability to handle different ISO settings. A better camera will let you shoot at both higher and lower ISO settings than normal.
Why mess with ISO?
In many instances, the use of flash to achieve a certain exposure is not desireable, practical or allowed so you must use lower ISOs in order to get proper exposures without flash.
About Red-eye control
Flash, especially on-camera flash has a couple of effects on photography. One of the most obvious is the dreaded red-eye. When you see red-eye in a picture, you're seeing the flash illuminate blood vessels in the retina. This becomes more problematic when your pupils are dilated, and remember that in lower light conditions (when you would need flash for a proper exposure), pupils are always bigger and more prone to red-eye.
If you can't control the size of your pupils, the easiest way to combat red eye is to shoot without flash at lower ISOs. You might need a tripod in order to accomplish this, especially when people are involved.
The Inverse Square Law
Another case when you have to switch to a lower ISO plan is because of the waning strength of flashes. The inverse square law of light intensity says that an object twice the distance from a light source will receive a quarter of the amount of light. In other words, light intensity diminishes dramatically with distance, so at a certain distance, no matter how powerful your flash is, it won't be able to reach your subject at enough intensity to make an impact.
At certain events like Theater performances, indoor sports events like gymnastics or some concerts, Flash is considered too disruptive for the performers and therefore not allowed. In those instances, a low ISO number will allow you to shoot faster.
Negative Effects of ISO
If ISO is so good at allowing you to shoot pictures in lower light at faster shutter speeds, then why not shoot at low ISOs all the time? The most obvious effect of ISO on your photos is on image noise. Simply put, the higher your ISO and the lower your ambient light, the more noise your images will appear to have. Higher end cameras will handle noise better than cheaper cameras, and notice in the sentence above, if you have somewhat decent light at a higher ISO settings you can still get good exposures.
Consequently the lower the ISO setting, the clearer your images. You should shoot at the lowest possible ISO setting. Most cameras will have an ISO limit of 100, but some higher end ones will allow shooting at lower ISO settings.
Sometimes you need to limit the amount of light as much as possible. For example in full sun, a low ISO settings will yield very bright images, so you have to shoot. A lower ISO settings would affect your exposure and allow you to shoot at slower speeds or lower F-stops (to get a narrow depth of field).
Another control that will affect the look of your photos is white balance. Light in different places and at different times of the day has different color casts. Flourescent lighting, for example, has a green tint, while tungsten (regular light bulbs) have a yellowish cast.
Your eyes automatically ajust to white balance variances so we dont see these casts, but cameras do record it. So a white sheet of paper always appear as a white sheet of paper to us.
Most of the time, shooting in Auto white balance is good enough. If you're a perfectionist, a lot of cameras allow you to adjust your white balance settings by shooting something that's supposed to be white and calibrating the shots to that.
One instance when you may have problems shooting is in mixed light situations. If you're shooting somewhere with tungsten lighting and a window, you have two light sources with different colors. There's not much you can do in those situations except than to balance for the dominant light source.
Creative White balancing
When you're shooting flash, you should also gel your flashes to match the current ambient light. So if you're shooting under flourescent lighting, you should gel your flashes with green so that both of the light sources are similar, then set your camera for the flourescent preset. When shooting under tungsten lighting, use an orange gel to color correct for the warm light.
You can achieve some creative light effects by sometimes playing with these gels. One you might be familiar is to make sky look bluer than normal. If you gel your flashes with orange gels, set your camera for tungsten light, then shoot someone in regular daylight, whatever you light with the flash will look the right color, but whatever the sun is lighting will have a blue cast to it. This can make a dull sky look more blue and is a common trick among photographers.
Most cameras, especially lower end cameras shoot in the JPG format. The jpeg format provides extremely small files sizes while maintaining fair image quality, but there are some sacrifices that have to be made. The image sensor in your camera is capable of shooting much more information than what JPG can hold. One of the many advantages of shooting in RAW format is that you can easily adjust your color balance after you've taken the picture without a loss of quality.
It's important to take a minute before every session and set some of these variables BEFORE you begin shooting. Once you've started a session, it's hard to think about these things so make sure you set the following every time you switch to a new location during a shoot.
- Camera Resolution
- ISO setting
- White Balance