What is ISO for DSLR camera?

The letters ISO on your digital camera settings refer to the film speed. Even though your camera is most likely not film at all, but rather digital, the ISO setting still does has the same function as older film cameras. ISO determines how sensitive the image sensor is to light. If your after more technical information, Wikipedia has a good article on ISO speed.

THE MOST COMMON ISO SPEED SETTINGS

100, 200, 400 and 800. The ISO number indicates how much light your camera�s sensor can absorb.
Depending on your digital camera model you may also have them in the range of 64, 100, 160, 200, 400, 640, 800, 1600.

GENERAL RULES AND TIPS FOR ISO SETTINGS

* Use an ISO of 100 or 200 when taking photographs outside in sunny conditions.
* If the sky is overcast or it is evening time, then use an ISO within the range of 400 to 800.
* Night time or in cases of low light you might need to set your digital camera ISO to 1600. If you don�t then your photo will appear too dark if at all.

HOW DOES THE ISO SPEED AFFECT THE PHOTOGRAPHS END RESULT?

If you set your digital camera to a low ISO, for example 100, the resulting photograph will be better quality than one set at 1600. The higher the ISO the more grainy the photo will look. Therefore go for a low ISO number whenever possible.

However there are circumstances where a lower quality photograph is better than none at all. For example taking photographs of fish in a dark aquarium would normally be out of range for most point and shoot cameras. As you can see by the image below, setting my SLR camera to a high 1600 ISO made this task possible. Otherwise there would not have been enough light let in to the sensor and the image would have turned out totally black.

WHEN TO USE YOUR ISO SETTING?

1. If you want to ensure the highest quality photograph possible.The lower the ISO the better the quality. An ISO of 100 or 200 will give you a better quality photograph than one set at 1600. If the image is destined for website display, then this may not matter. However, if you wish to print the photograph, then you�ll want to keep the ISO low. Otherwise it will look grainy or noisy (as it�s also refered to).

2. If you want to take a photograph in dark situations and not use a tripod.For example, if you were on a tour through a mountain cave or at an aquarium, a tripod may not be feasable. In these cases you could up your ISO to at least 800. This way, your camera will automatically keep to a fast enough shutter speed for you to hand hold your camera. Yet still allow enough light in to your camera�s sensor for a reasonable night shot. As explained in the first section, this would cause a grainy photograph. However, in some circumstances any photo is better than none.

3. If you want to take photographs in darker situations other than outdoors, without the use of a flash.For example, if you were taking images in a museum or theatre, camera flash could be prohibited. Or if you were photographing a child blowing out their birthday cake candles. A bright flash could ruin the atmosphere. In this case you would keep the ISO at around 800.

4. If you want to take a photograph indoors of a moving subject.For example, if you were taking photographs of a basketball game at an indoors sports center. In these circumstances there isn�t always enough natural light to take a good photo, while at the same time the players aren�t going to stand still long enough for you to shoot at a slower shutter speed either. Therefore, you could up your ISO to around 800. Again, this would allow enough light in to your camera�s sensor for a reasonable shot.

The Purpose of ISO

Being able to change the ISO on your digital camera is most useful in situations where there isn�t a lot of ambient light.

Cameras have four ways of gathering more light:

• Increase the opening of the lens (aperture)
• Increase the time the sensor is exposed to light (shutter speed)
• Increase the sensitivity of the sensor (ISO)
• Create artificial light (flash)
  

The most common thing that happens when there isn�t enough ambient light is that your shutter speed slows down to let more light hit the sensor.

Here�s the problem: this leads to blurry photos.

When the shutter stays open for long periods of time, it captures motion as blur. ISO 3200 let me capture this shot at night with overhead lighting

If your subjects move when you take the shot, they appear blurry. If you�re holding the camera in your hands, the entire photo is blurry (due to camera shake).

ISO solves this problem.

Since the sensor becomes more sensitive to light, the shutter doesn�t have to stay open for long periods of time.

Voila! Clear photos even in dim light - without using a flash.

Want an extreme example? With your camera set to ISO 1600, you should be able to take clear photos indoors at night using overhead lights holding the camera in your hands.

Like many other things in life, you don�t get this amazing benefit without some consequence.


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