High ISO: How high is high enough ?

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This is the way to avoid speckling and insipid colours

High ISO: How high is high enough ?

We seem to live in a camera world with untold possibilities. Whilst photographers had mainly to be satisfied with ISO 400 sensitivities when films were analogue, extreme settings of ISO 12,800 or 25,600 can be chosen today on modern system cameras. The high ISO values can be activated with just a few keys. However their high sensitivities result in a loss of picture quality which can be considerable, so they should only be used in exceptional circumstances.

Read below on how to set the ISO value at any time so you always get the best possible image outcome whatever the situation.

Basically, a high sensitivity such as ISO 800 points to the fact that the sensor needs less light than with a low sensitivity such as ISO 100. Conversely, the high ISO values are thus useful when taking photos on a rainy day, indoors or at night. A high ISO number ensures a sufficiently short shutter speed so to manually continue taking focussed shots.  But remember - the higher the ISO value is, the more the image quality will suffer. Definition, dynamic extent and colour saturation will be markedly reduced.

The best images come about from cameras with the lowest possible sensitivity - i.e. usually an ISO 100 to 200 value. The two most important rules of thumb can be derived from this:

  1. The ISO value should be kept as low as possible.

  2. It should only be raised when the shutter speed is too long for a blur-free shot.

Therefore glance at what the exposure parameters indicate before taking a picture. There is every chance of the picture being blurred if the shutter speed is more than 1/60 or 1/30 of a second. Therefore you should raise the ISO value. Doubling the ISO number (e.g. 200 > 400) always brings about an exposure time which is half as short (e.g. 1/60 s > 1/125 s).

Of course in practice it is not always easy to glance at all the settings. Choose the "ISO Auto" setting if you prefer to concentrate on the motif rather than the technical parameters. The camera then automatically regulates the ISO value depending on the prevailing light. Although this is practical there is still the risk of the camera selecting an over-high sensitivity with the attendant quality of the photos continuing to suffer. You can avoid this by establishing the "Maximum sensitivity" in the camera menu under "Sensitivity settings". Select a value providing an acceptable balance between high sensitivity and sufficient picture quality - such as ISO 1600.

The extent to which you can go with the ISO value depends on your camera and your personal preferences. Find this out by taking photographs of a motif under various sensitivities and assess image quality with a 100% view on the screen. Make a note, in particular, of the dark parts of the image. Consciously setting the ISO value will certainly help you in getting the best possible image quality whatever the shot.

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