Cameta 101: Understanding ISO

ISO is one of three components that makes up the exposure of an image. By having a better understanding of ISO and how it affects shutter speed and aperture, you will have more control over your pictures. I’m going to break down the mysteries of ISO and explain how to finagle the settings to get what you want. If you’re shooting inside, in the bright sunlight, at night or fast-moving athletes then it’s important to understand ISO so you can get the best shot possible.


In digital photography, ISO is the sensor’s sensitivity to light. ISO numbers generally go as low as 100 and can go as high as 3,280,000 (such as in the high-end Nikon D5). The higher the number, the more sensitive it is to light, and the more digital noise. If you don’t know what noise is, well, it’s like grain on film. Sometimes having a little noise can make a picture more gritty, and it can really work visually. Other times, all it does is decrease sharpness and overall quality. Also, there’s color noise that essentially produces pixels of random colors in your image. Honestly, I can’t think of a way this would look good.

1/15 SEC. F/5 @ ISO 400

What’s a good ISO number to start out with?

ISO 100 is a good starting point that will give you little noise and smooth images. This ISO setting is preferred for landscapes, portraits and macro work where a fast shutter speed is not needed. You will quickly see if this will work with the environment and subjects that you’re shooting.

1/400 SEC. F/5.6 @ ISO 100

When should I use a high ISO?

A higher ISO number will increase the sensor’s sensitivity to light. You want a higher number at night or dimly lit environments when you need to shoot with a faster shutter speed. The interior shot below was taken at a dark restaurant. I wanted to shoot at 1/60 second because I didn’t have a tripod, so I raised the ISO to brighten the exposure.

1/60 SEC. F/3.5 @ ISO 2000

The picture below was taken on a cloudy day, and the biker was zooming by. I wanted to shoot at a fast enough shutter speed to freeze the action so I put the ISO up to 6400.

1/125 SEC. F/4 @ ISO 6400

When should I use a low ISO?

Digital sensors perform well in daylight, so if it’s nice outside and your subjects are still, like the pumpkins below, then a low ISO such as 100 will work well. A low ISO will give you high-quality pictures with little to no noise. Also, if you’re shooting in a studio and you want to have the best quality pictures possible for professional use, use the lowest ISO that your camera is capable of.

1/400 SEC. F/4 @ ISO 100

What are problems that arise if my ISO is too high?

The higher the ISO the more noise you will get. Sometimes it’s not detectable, but if you push your sensor’s sensitivity too high then you’re going to get noise. The pictures below were shot with the same f/stop number, but the image with the lower ISO appears smoother with better detail. I could throw out some ISO numbers to avoid, but every camera has a different sensitivity.

If you want to test out ISO numbers, put your camera on a tripod and take a picture at ISO 100, then take the same picture at ISO 200, and so on until you get to the highest ISO possible. Then, look at the pictures on your computer, zoom in and check out when the noise starts to appear. Is it pleasing to the image or does it take away from the quality? Obviously, this will differ depending upon the lighting situation, but it’s a good start.

ISO 100 @ F/8 (click for detail)

ISO 25600 @ F/8 (click for detail)

Doubling ISO

Let’s say an image shot on a bright day at 1/125 sec. at ISO 100 has perfect exposure. If I double the ISO to 200 then I have to double the shutter speed. So, the new setting will be 1/250 sec. at ISO 200. I know it can be a little confusing. Just remember that the higher the ISO the faster you can shoot. If the sensor is more sensitive to light then you don’t need as much light exposed to it. Hence you can shoot with a faster shutter speed or a smaller aperture opening.


I hope this has cleared up the confusion about ISO. If you’re shooting fast-moving subjects then you want to raise the ISO so that you can shoot at a faster shutter speed and freeze the action. Just be careful about raising the ISO too high because you’ll get more noise the higher you go. If you’re shooting landscapes on a bright day then use a lower ISO so you can get the most amount of detail. Keep experimenting and soon you’ll be able to manually control your ISO, shutter speed and aperture to take your photography to the next level.

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