Digital Photography: ISO and What does it mean?

With the sensor technology becoming a very important issue in digital photography, it is important to understand what this means for your photographs and for your new camera selection.

ISO, what is it?

If you try to track down the definition of ISO, you’ll be met with a lot of confusing mathematical terms and definitions that do a great job of telling what engineer-speak ISO settings are for you camera.  I’ve never been much for extremely difficult to understand definitions.  So, here we go with the basic one.

ISO is the comparison for the sensitivity of the film you used to use in an old-school film camera.  The lower the ISO setting on the camera, the less work the camera has to do to “read” the image in front of it.

For those of you who remember the 35mm camera, you would purchase film with an ISO or ASA rating:  ISO 100 was for bright sunny days, ISO 400 was generally an all-purpose indoor/outdoor film, ISO 800 or 1600 was great for shooting nighttime pictures and fireworks.  If you had an ISO rated film that was incorrect for the type of picture you were shooting, you had to change the usually incomplete roll of film in the camera and start shooting with a brand new, (ISO corrected), roll of film.

With today’s new ISO equivalent cameras, the settings are unbelievable, now the ISO ratings are in excess of 12,800.  You can almost shoot in the dark.

But…,  here it is… the but.  Usually, with the higher ISO setting used on the camera, the camera sensor has to work much harder, and the pictures taken will show a type of “graininess” that makes your picture look like it was taken with a 1930’s newspaper camera and some of this graininess or “noise” can be eleiminated from your image, but with this eleimination of “noise”, comes a loss of detail or sharpness.

Warning:  Technical information ahead:   Basically, what happens is that the electrons inside of the camera have to work harder to “read ” the image in lower-light situations.  This electron noise is caused by the electrons on the sensor heating up the sensor and leaving heat footprints from how hard they worked to do the job for you.  The best possible solution, when it is feasible, is to make the camera sensor work less to capture a sharper, “noise-free” image.

So, the rule to remember when setting your own ISO setting on the camera.  Use the lowest possible setting to get a good picture with your particular camera.  Digital photography magazines and websites will often offer a “noise” comparison example for the specific model of camera you are looking at, and they are a great way to preview the specific camera’s highlights and weaknesses  relating to digital noise.

Hope this helps, take better pictures and have fun.

Dewayne Chriswell

Digital Photography Basics , , , , ,


  1. Thank you for always giving me in-depth knowledge on how to pick the right camera that takes the best pictures.

  2. SO THAT’s what those numbers are??? I always bought 400 – not knowing why or what it was – because I was told that’s what I should use. NOW I understand why the pictures look dark when taken indoors without too much lighting … Thanks, DeWayne, this was really helpful!

    Best, Neil

  3. And here I have spent my entire life believing that ISO stood for Insurance Services Organisation (the place where I ordered my insurance apps from)!! Learn something new every day!
    Sonya Lenzo

  4. DeWayne,
    The quality of the old 35 mm printed was pretty amazing. When digitals came out printing off the computer was pretty bad. Now I see the quality coming up.
    Are there any film cameras or film technology that is superior to digital print quality? Have we come to the point where digital tech is the obvious choice all the time?

    • Kevin,
      Purists and artisans will always be able to pull off the most amazing feats, no matter the medium. The thing I enjoy most about digital photography is it steps up the learning curve making the lessons much easier, much cheaper and more exciting. The “which is better” argument is going to go on for a long time, as digital photography is still in its infancy. This particular transition has caused some veteran photogs to just up and quit rather than embrace or try to compete in a new market. Think back to the days of the Apple IIe, or the Commodore 64. We’re just moving past that stage now. It’s a brave new world and there’s room on board for everyone. For those who still embrace the medium-format, the 35mm, even the 110s, there has always been an artistic flair to those cameras, and talent/creativity should always be acknowledged. Much in the same way hand-styled calligraphy can never be replaced by computerized fonts, we can appreciate the artistry and also realize most of us will never achieve that level of finesse without years of expense, (time and money).

  5. Dewayne, Thanks for sharing what ISO on a camera does. I think this should clear up the confusion.
    Scott Sylvan Bell
    Now go implement!

  6. Clare Delaney-Young

    Your non-engineer-speak explanations are excellent, and this post on ISO is no exception, thanks!

    For Everything Eco-Friendly

  7. Hi Dewayne,
    I never took the time to understand all the feautures of a camera. Thanks for explaining what the ISO means, now it makes sense.

  8. Kevin Bettencourt

    I worked in a photo lab when I was young and saw the results of poor film choice first hand. Thanks for the heads up.

    Las Vegas Air Conditioning Services

  9. I love how you teach the complex in a way us simpletons can understand…

    Sales Expert

  10. Thanks for explaining what ISO is and what it means. I really got a kick out of the Warning: Technical Information Ahead 🙂

    Good stuff Dewayne!


  11. That was a good blast from the past . My younger brother used to develop old films in his dark room , so learnt a lot from him .

  12. Thanks for the explanation. I always thought the ISO was a function of the film and not of the camera settings, which I guess was true of film cameras. You made it easy to understand.

    Steve C

  13. Thanks for explaining ISO as I am worse than a beginner but you are bringing me up to being a novice…who knows if we can go beyond that!

    Jen B
    Tinnitus and Hyperacusis

  14. Hi Dewayne.

    Thanks for making ISO clear.

    Happy Dating and Relationships,

    April Braswell
    Internet Dating Safety and Security Tips