Understanding ISO Settings in Digital Camera

I’ve seen many people scratching their head over one setting in their digital camera, the ISO Settings. For many, it’s a complete alien terminology and they fail to use this setting to the hilt to take photographs. If you also have never been able to decode the ISO Settings, keep reading…

What is ISO ?

The term ISO dates back to the era when cameras with light sensitive films were used. According to wikipedia, the definition of ISO in relation to the light sensitive film is:

Film speed is the measure of a photographic film’s sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system.

Since we no longer use those cameras, ISO now refers to the sensitivity of your digital camera’s sensor. ISO is measured in following sequence of numbers in your digital camera:

80, 100, 200, 400, 800, etc..

This measuring is directly proportional to how sensitive the image capturing sensor of the digital camera is at that particular instance of time. Obviously, low ISO numbers (80, 100) correspond to less sensitive camera sensor and the higher ones (400, 800) corresponds to high sensitive camera sensor.

How does it affect the picture quality ?

Interestingly, ISO has a direct effect on the quality of the photographs you take. At lower ISO numbers, photographs come out to be clean and crisp (owing to the fact that the camera sensor is less sensitive) and at higher ISO numbers, photographs come out to be grainy (because we have a very high sensitive camera sensor)

However, you have to use the ISO settings in accordance with your Aperture and Shutter Speed settings. A lower ISO (which gives better and clear photographs) require Shutter Speeds and wider Aperture. A high ISO (which gives grainy photographs) gives you freedom to use a high Shutter Speed and a low Aperture value.

When does it matter the most ?

If you mostly shoot in outdoors in bright light, you don’t have to worry about your ISO settings. In fact, you can leave your digital camera in auto mode and let it select the best ISO for the scene. However, if you don’t have plenty of light, you have to tweak your ISO settings.

Let’s take a scenario. You are in a music concert and there is not much lights among the spectators and all the lights are on stage. Now, if you want to take a photograph of your friend standing at some distance from you in the audience, you have to rely upon the ISO settings a lot. Here is what will be happening:

  • You choose a slow (or normal) Shutter Speed and Aperture value and your camera gives a warning that your photograph will come out to be blurred (mostly, a red signal will flash on the LCD screen). That’s indeed true because there isn’t ample amount of light that should fall on the camera sensor.
  • If you increase your Shutter Speed without increasing the ISO, you will have underexposed photographs since the Aperture value is already to it’s maximum (that means, the lens is open as wide as it can to allow maximum possible light).
  • You’re stuck with everything and you can’t take a photograph without tweaking your ISO. That’s when the importance of ISO creeps in. Since you can’t do pretty much with your Shutter Speed and Aperture values, it’s time to levitate your ISO Settings. Remember, by increasing the ISO, we are making the camera sensor more sensitive to the available light. It’s also logical since we don’t have ample amount of light and we have to take the photograph anyhow. But, we have to compromise slightly on the image quality as there will be a small amount of grains involved due to high sensitive camera sensor. But, a grainy photograph is better than no photograph at all. Isn’t it?

What value of ISO is acceptable ?

That really depends on what type of camera sensor you got. If you have a high end DSLR camera, even the 1600 ISO shots will be perfect. But if you have an average level point-and-soot camera, you can only expect nice photographs in a range of 80 to 200 ISO. So, you have to take test shots with every ISO settings to ensure that you decide an optimum level of acceptable ISO with respect to your camera.

Where to use what ISO ?

Situations where you should use a low ISO;

  • If you are outside and there’s plenty of sunlight
  • A room which is brightly lit.
  • Any area having ample amount of light falling on the subject.

Situations where you have to have a high ISO

  • Music concerts
  • Birthday Parties
  • Hotel Interiors
  • Any place having inadequate amount of light


ISO wasn’t so tough to understand. Was it? Well, I’m sure by now you must have a fair idea of what ISO is and what it does. You have to really experiment yourself with your camera for the ISO levels because as stated above, it all depends on the type of camera you have.

6 thoughts on “Understanding ISO Settings in Digital Camera

  1. Sibilio

    I truly loved this brilliant article. Please continue this awesome work. Regards, Duyq.

  2. Amitabh Bacchan

    Nice Article Rish !

    Can you also add why EV and ISO are NOT the Same , some of my friends consider it as Same , and I am tired of explaining why they aren’t.

  3. Rish Post author

    Thanks Amitabh. I’m glad you found the article useful. And yes, many people have confusion between EV and ISO. I’ll write a post about that soon. Thanks for bringing that into my attention 🙂

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