Fordele og ulemper ved høj ISO-værdi

If the light is dim you should go for higher light sensitivity (ISO). This may sound quite simple, but you actually need to give this some serious thought before you start shooting. Using high ISO values will make shooting in dim light surprisingly easy, in the long run it may however lead to disappointing results.

What Is ISO?
Before the advent of the digital camera the light sensitivity of film was indicated in ASA (an abbreviation of American Standards Association) based on an extensive project initiated by KODAK. ASA was sometimes referred to as ISO (International Standards Organization). In those days, if you wanted to adjust light sensitivity while you were busy shooting you had to change your film.

Even though a digital camera does not use any film it was decided to continue to refer to the old standards for practical reasons. The camera allows the photographer to choose from a series of values that are equivalent to the old ISO values such as: 100, 200, 400, 800 or 1600. The higher the value the more light-sensitive the camera sensor will be. The higher the value the less light it takes to get a correct exposure.

The light sensitivity of the digital camera is controlled by a single touch of a button.

ISO Gives You Flexibility

All photographers rely on light, and available light may vary a lot depending on the locality or the time of day. For this reason ISO values are an important tool that enables the photographer to work effectively in many different lights.
The ISO value influences shutter speed and aperture in every shoot. In the heart of the rain forest, at a concert or during a walk in the moonlight, i.e. in situations where little light is available, this tool will make it possible for you to get good photos without having to use a tripod. This is one of the ways in which the digital camera has made being a photographer much easier.
ISO is a tool that will also be useful when you are shooting in situations with plenty of light. Selecting a high ISO value and shooting in the middle of the day will allow you to get very short shutter speeds, this will come in handy for sports photography or action photography.

This photo was exposed in evening light at ISO 800. Despite the dim light the subject appears quite frozen.

Auto ISO

Many digital cameras have a mode called Auto ISO. Using this setting the camera will automatically increase ISO values whenever the available light makes it necessary. We generally do not recommend that you leave this kind of decision to your camera. Instead you should get in the habit of paying attention to your surroundings, to light, and to shutter speed.

The Dangers of a High ISO Value.

Being able to adjust light sensitivity as you please is nothing short of fantastic, but everything comes at a price. When you increase light sensitivity you enable the sensor of your camera to register quite weak sources of light. This may in some cases affect image quality.

Shooting at very high ISO values, or at very long exposures, will cause noise. This unwanted noise can cause a photo to become grainy or it may cause parts of a photo to be of a wrong colour. Unfortunately, the higher the ISO value the bigger the problem.

How much noise your camera will actually produce at high ISO values depends on the make of your camera, the model, and most importantly, the size of the sensor. New camera models have improved significantly and they will allow less noise than old models. The larger the individual dots (pixels) are the less the tendency for noise to appear will be. This is why dSLRs produce considerably less noise at high ISO values than compact cameras do. Besides, professional cameras are constructed using components of a better quality and they are equipped with image processors that use highly developed noise reducing algorithms. For this reason, professional and semi-professional dSLRs, in general, produce much better results in all of the ISO range.

Take the two photos below, both are of the same subject.

ISO 200.

ISO 1600.

The difference between the two photos is plain to see. However, you need to get really close to see how much noise is actually present in the last photo. Take a good look at the two enlarged sections of the photo below.

You may not be able to see the noise when you are actually shooting. The LCD on the back of your camera is simply too small to reveal these details. You may not even be able to spot the noise when studying your photos on a computer monitor. The problem will, however, become apparent if you try to make a large print of your photo or if you try enlarging it. Consequently, the larger the print you want, the more attention you need to pay to the problem.

If you want to make absolutely sure you avoid noise you should always choose the lowest ISO value that is possible in a given light. When you have read about ISO values the next step would be to read about using a tripod.

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