Choosing the Right ISO Setting
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While many people may be familiar with the term, ISO originally had nothing to do with photography directly. ISO is an acronym which stands for the International Organization for Standards. This organization was founded in 1947 and is responsible for developing and maintaining industry and international technology standards. The relevance to photography came from a specific standard: ISO 5800:1987 is the standard set for defining light sensitivity of photographic negatives. Film negatives are defined in units of ISOs as defined by this standard. Light sensitivity settings are defined as a number based off the ISO standard. ISOs are identified as a number ranging from 6 to 6400. The higher the number the more sensitive the film. Higher sensitivities mean that the shutter has to be open for less time to absorb the same amount of light. This allows for fast action shots or shots at lower light without a flash. On the other hand, higher ISO films tend to be grainier and have more ambient noise. Finding the balance between ISO and shutter speed is one of the most important skills of a photographer.
How does this help me take digital pictures?Of course nowadays fewer and fewer people take photographs with film. Digital cameras also feature a setting called ISO. This is based on film negatives and is the setting for light sensitivity for the digital image sensor. Most cameras range from ISO 80 - ISO 1600 with only extremely high end models shooting at higher or lower ISO settings. There is also an ISO setting for Auto which lets the camera pick its own ISO. This option is fine for most people or those who just want to snap quick pictures.As a general rule higher ISOs should be used for low light situations and situations where a flash can not be used. Also high ISO settings may be helpful for shooting high speed action. Lower ISO settings are useful for bright situations such as sky photography and bright days. The lower ISO settings will tend to be smoother but there is a higher possibility for a blurry image. Higher ISOs tend to be a bit grainier. Because lower ISOs tend to take cleaner, higher quality images, it is generally a good idea to shoot at the lowest ISO appropriate for the lighting conditions. Higher ISO settings should be reserved for low light situations or high speed subjects such as athletes. Of course you should experiment with different ISOs to see what different effects they produce.
What about Shutter Speed?In any discussion about ISO or film speed it is essential to at least touch upon the topic of shutter speed. If film or sensor speed refers to the light sensitivity than the amount of light which the film or sensor is exposed to will drastically affect the image itself. Faster shutter speeds will mean less light reaches the sensor. Slower shutter speeds result in more light bombarding the image. If you are using a low ISO you can try a slightly slower shutter speed to get more light onto the sensor. If you try this be careful about stabilizing the camera to prevent blur. Inversely, if you use a higher ISO setting you can try a faster shutter speed because the increased sensitivity of the camera sensor requires less light to capture an equivalent image.An in depth discussion of shutter speed is beyond the scope of this article, but there is a very useful tool developed by Ken Milburn of DesignMentor Training which lets you choose the ISO and the light conditions and then gives you recomendations for shutter speed. You can even dictate if you are trying to achieve super crisp action shots or slightly more blurred shots. Check it out here: Digital Photography Exposure Wheel - DesignMentor Training |