ISO Explained!

Filed in Tips by 51 Comments
ISO Explained!

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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About the Author ()

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+.

Comments (51)

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  1. Tsebo says:

    Thanks for this David. Very helpful.

  2. kimaru says:

    thank you

  3. Juvy says:

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

  4. 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

  6. test says:


  7. Earl Sharpe says:

    Great refresher as many have pointed out. 2 things I’m stuck not understanding and can’t seem to get a grip in are using a flash other than the cameras and 2. How I’m going to have to set my Canon T2i up for shooting night time pictures at Charlotte NC during the All star race come end May.
    Ie gotten fire works down and some low level lighting pictures but nothing travelling at 195 miles an hour with hundreds of point and shot cameras flashing around me.
    Anyone with any suggestions or has this topic possibly been covered somewhere David before

  8. Ahmed albaqer says:

    Amazing tips David .. Thanks v.much

  9. Greg says:

    very good stuff, thanks for the help!

  10. kreng says:

    2 thumbs up! ^^

  11. savio andrades says:


    I am being following your tips since 2004 – 05 and found it really helpful. Infact i am now giving tips to other aspirants! Thank you very much!

    Savio Andrades

  12. JRoberto says:

    It is without doubt an interesting tip; it is very helpfull to work out nice shots right way from the camara by just balancing iso and speed. thanks!

  13. Mike says:

    Hello Krishnan,

    I think you advice to hamid may be incorrect. First, the Speedlite 580ex is made by Canon. It may be more appropriate to reccomend a Nikon SB900.

    Secondly, ISO 1600 on a D70? On a D700 OK, but for D70 there is a lot of noise at ISO800 and ISO1600 would be much worse.

    I’d recommend, with a flash and tripod to take the following steps. (I’m assuming your subject is a person against a night time cityscape.
    1/ Set the camera on a tripod
    2/ Set aperture to f11 (this i agree :))
    3/ use spot metering. Choose a spot on the background and adjust your shutter speed to that your exposure meter indicates that the background will be exposed properly. Recompose your shot (You can forget about the meter now)
    4/have your flash on the camera. Personally I like manual mode. Set the power to 1/32 or 1/16 or so.
    5/Take the photo. The background should be fine. If your subject is too dark, open your aperature more, like f8 or f5.6. If your subject is too bright, close the aperature more, like f11 or f16.

    Keep in mind the distance between you (and your flash) to your subject. The farther way, the darker the subject will be…


  14. seema says:

    This is one of the best sites ( for digital photography) that i’ve been to. The concept and detailed explanation behind it is excellent!

    Keep up the good work!!

  15. krishnan says:

    Hello Hamid,

    Lighting is not a problem. u can use a SppeedLite 580X for a better lighting. Set your camera to ISO1600 if it is for night shot. and to achieve a sharp image use F11 with a lower shutter speed. Use AV setting it will be very appropriate.

  16. krishnan says:

    ISO is once area you can manipulate. view my photos then you will know how to take night photos. I normally use manual and set a low speed in dark areas shutter speed 1/50, F11, ISO 1600
    This is sufficient for various shots including Formula One sports at night.
    All this I learnt from David only. Just sharing the knowledge with you guys.

  17. Julius says:

    Thanks for the tips.I learn a lot.

  18. Jacob says:

    Great tips and advice!

  19. hamid says:

    i have nikon d 70 camera but i have least of experiance about lighting.could you give me some tip about lighting,

  20. Alejandro Lopez Fenner says:

    Dave. Thank you for your tips! I have tried some of them like using ISO 400 for indoor pictures with fantastic results. Your work is very inspiring to us photography lovers! Keep up the good work.

  21. julesh shah says:

    thanks a lot dear …. as you are spreading very informative knowledgable tips to the people

  22. photogphy says:

    Thanks for the tips

  23. Garie says:

    If I’m photographing a night scene for instance, I just put my camera on a tripod and lenghen my shutter speed until I get a good exposure. By bypassing the ISO setting and going this route, am I not avoiding most of the noise problem?

  24. Prayank says:

    I am amazed and happy to recieve your tips.

    Amazed – as I was not aware that photography can be an Art in true sense.
    Happy – as I am pursuing in Photography with a DSLR and I need such tips as many as possible.

    Grateful to you David for these basics. I am excited to do photography…

  25. Pat says:

    David, love your tips.

    thank you.

  26. NOBBY says:

    Great tips as ever !

  27. Eze A. Obulor says:

    I think you’re a rare person among many. The tips are very inpiring, making one like going out to experiment knowledge gained from the tips as am going out to try out the tips on ISO for night shots.
    I think I owe you alot. Keep it up.

  28. Rose says:

    love your tips your the best…..I have an Canon Power shot SD870 IS
    maybe one day you can discuss it…..thanks eh

  29. Tayo says:

    You are a great and dependable teacher!Thanks for your support

  30. Terry says:

    The tips are very helpful. As a progressing photographer I’ve employed many of the tips improving my shots from very good to great delivering a better product to my customers, while also decreasing the time I spend editing after the shoot.

  31. Is ISO setting helpful for controling depht of filed? If I use a lower ISO, I’ll need a greater aperture setting, for the same shutter speed, this will reduce the focus range, correct?

  32. Elaine,

    As I say in my tip, Auto ISO is a good thing most of the time. Your camera will automatically select the correct ISO for the scene you are shooting.


  33. Elaine says:

    What about auto ISO!!! Is it good or bad?

  34. KHALID says:


  35. Matt says:

    Thanks for the tips they are great. Do you have tips for a more advanced photographer.

  36. nazaruddin says:

    I use to play around with ISO on my digital camera. Till your tips, i now understand why everytime i change the setting, the output is different. Your tips really help and useful to me. Thanks a lot.

  37. angela connery says:

    Love your tips!!!!!

    Very helpful

    thank you!

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