ISO Explained! :: Digital Photo Secrets

ISO Explained!

by David Peterson 44 comments

You are probably familiar with ISO on film used in a film camera. It's the 'speed' of the film - higher ISO values mean you can take photos in lower light.

But what about in the digital world?

Surprisingly, there is an ISO setting on your Digital camera. And although there is no longer any film, the ISO setting still plays a vital role.

ISO indicates your digital camera's sensitivity to light. The higher the number, the less light is needed to take a photo that is correctly exposed (not too dark or too light).

In bright light (like the middle of a sunny day), you'll normally use ISO 50 or ISO 100. These lowest settings can be used because there is lots of light around.

However, in lower light, your camera needs some help. There are two ways of doing this:

Decrease Shutter Speed

With a slower shutter speed, the camera has more time to 'take in' the amount of light it needs. Unfortunately though, the slower the shutter speed, the more chance that your images will turn out blurry.

Increase ISO

Rather than decrease the shutter speed, you can increase the ISO. As I said above, this will increase the sensitivity of the camera which means you can get the same shot with less light entering the camera. Thus the shutter speed can be kept low enough to avoid blurry images.

As increasing the ISO will increase the shutter speed, a high ISO will also help when taking fast moving sports shots. You'll get clear, crisp shots with no blur.

However, I still recommend you use the lowest ISO possible. Why?

Problems of using a high ISO

Using a higher ISO means the camera has less light to work with. Unfortunately this also means that 'noise' is introduced into your camera. If you'd like to find out exactly what noise is and how to eliminate it, check out the free bonus on noise that comes with my Digital Photo Secrets book.

Your camera's highest ISO value will produce a lot of noise in your image, so I suggest avoiding them unless the light is so low that you have no other choice. Instead choose the second highest value (second largest number).

Auto ISO

Fortunately most of the time you don't need to worry about selecting the correct ISO. Most cameras have an "Auto ISO" setting. With Auto ISO, the camera will look at the amount of light in the scene and change the ISO appropriately so that the shutter speed doesn't get too slow.
ISO Values

If you choose to use a manual ISO, what values should you use?

ISO 50-100. Suitable for bright light (like outdoors on a sunny day).

ISO 200. Great for overcast or cloudy days.

ISO 400 and 800. Use these values when the light is getting dim but it is not yet night.

ISO 1600 and above. Use for indoor or night shots. Also useful to freeze the action in sports shots. These values will produce the most noise.

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  1. says:

    However, if you are outdoors in Bright Sunlight, then you need to turn the ISO down to a low value, or else your photo will come out all white and washed out with too much brightness.

  2. August Schunk says:

    I believe your explanation might help someone understand the concept of ISO as it relates to digital photography but it is incorrect to say that increasing the ISO setting increases the sensitivity of the sensor. The sensor has a fixed sensitivity and this can not be changed.
    Increasing the ISO setting only increases the gain applied to the image. Increasing the gain (ISO) above the lowest setting decreases the dynamic range. This is a trade off. We sacrifice dynamic range by increasing the gain by setting higher ISO settings allowing us to decrease the aperture and/or exposure time.

    • David Peterson says:

      Hi August,

      You are indeed correct. I talk about sensitivity of the camera rather than increasing gain because it's easier for newer photography students to understand.


  3. Howard in Edinburgh says:

    Thanks, David. A very clear explanation and you have moved me further along my photographic learning curve.

  4. HEMANTHA says:

    thanks for the help

  5. Tsebo says:

    Thanks for this David. Very helpful.

  6. kimaru says:

    thank you

  7. Juvy says:

    Wow! Thank you! You explained it very well especially to those beginners. Love your site!

  8. Nishi says:

    Well explained, easy to understand, thank u.


    I have problem with my iso settings , can any one help me pls..., sme tyms when i click the pic's ,pics becomes grainy so plz give me sm tips ,that hw can i eliminate grains frm my pic's ,and i always use iso at 100 or 200 in day then also my pic's become grainy,so plz give some tips and trick to make my pic beautiful by my NIKON D5100

  10. test says:


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About David Peterson
David Peterson is the creator of Digital Photo Secrets, and the Photography Dash and loves teaching photography to fellow photographers all around the world. You can follow him on Twitter at @dphotosecrets or on Google+.