Choosing the Right ISO Sensitivity Setting

Modern digital cameras allow you to select the ISO value for each situation using a dial or a button. This is a great advantage over analog photography, which requires either a film change or special development in order to alter the sensitivity base.

Figure 1-22: Detail of the same subject shot at ISO 6400

> Always select the lowest possible ISO setting and use a tripod whenever you can.

Generally, the lower your ISO value, the less noise your photos will display, resulting in better image quality. Higher ISO values always produce more noise, which takes on various forms and is usually more evident in darker image areas. Image noise is caused by charge differences between the individual elements of the image sensor that result from static, manufacturing tolerances, signal amplification, and other, similar factors.

High sensor temperatures also increase noise. If you are shooting in high ambient temperatures, keep your camera cool and don't leave it switched on for longer than absolutely necessary. The levels of noise a camera produces also depend on the type of sensor it uses. Small image sensors produce more noise than larger sensors, and CCD sensors produce more noise than their CMOS counterparts because they use more power and therefore have higher operating temperatures. Greater sensor resolution for a similar sized sensor reduces the per pixel sensor area, which also leads to increased noise - technical advances in recent years have helped to keep noise levels down in spite of increasing sensor resolution.

Grainy, "salt and pepper" noise effects are generally more acceptable to us because they look similar to the grain effects we know from analog film material.

If you find yourself needing to use higher ISO values (for instance, in low light or for fast-moving subjects) we advise you to use the best possible noise reduction tools during processing. (See also section 12.3, page 475 onwards.) We usually deactivate in-camera noise reduction, as it not only slows down in-camera image processing but also tends to blot out fine image detail. If noise reduction is really necessary, you can perform it in a much more selective and controlled fashion by using a RAW editor or Photoshop plug-ins.

We also nearly always deactivate Auto ISO. This feature allows the camera to automatically increase the ISO value if it thinks the situation demands it. This can be useful for sports photography or other fast-moving subjects, but it often produces unexpected, unwanted noise effects.

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Figure 1-23: Our first workflow steps on the computer: image transfer and management

Figure 1-23: Our first workflow steps on the computer: image transfer and management

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