DSLR Photographers: How to set your camera’s ISO

Wherever the ISO speed is located on your particular camera, its function will be the same: determining the sensitivity to light of your camera's light sensor. (Copyright 2012 / Andrew Boyd)

Wherever the ISO speed is located on your particular camera, its function will be the same: determining the sensitivity to light of your camera’s light sensor. (Copyright 2012 / Andrew Boyd)

Picking your ISO – the relative ‘speed’ of your digital captures—can be a source of confusion for beginning photographers, as I was reminded recently by a newbie DSLR shooter. He wanted to know how I go about deciding what ISO to use, and whether I changed it frequently during the course of a shooting session.

What great questions, I thought. This is something experienced shooters forget was ever an issue, but it’s something that’s fundamental to obtaining quality results. So here are the factors I consider when setting ISO speed.

ISO is expressed as a number that indicates the relative sensitivity of your camera’s light censor (CCD).  Most modern digital cameras have an ISO range from around 100 to upwards of 12,000.

The ISO 6400 frame looks pretty good in this full-frame comparison. Both images shot with a top-of-the line Canon Mark IV. (Copyright 2012 / Andrew Boyd)

The ISO 6400 frame looks pretty good in this full-frame comparison. Both images shot with a top-of-the line Canon Mark IV. (Copyright 2012 / Andrew Boyd)

The lower the number you set, the less sensitive to light your sensor will be. This means that you’ll need slower shutter speeds and wider apertures to capture a proper exposure. But your result will be an image with much finer detail and little or no discernible digital noise.

As you can see of this enlargement of the two images, the ISO 6400 image on the left contains a lot of digital 'noise,' while the ISO 125 image on the right does not. (Copyright 2012 / Andrew Boyd)

As you can see of this enlargement of the two images, the ISO 6400 image on the left contains a lot of digital ‘noise,’ while the ISO 125 image on the right does not. (Copyright 2012 / Andrew Boyd)

Conversely, the higher you set your ISO, the ‘faster’ your camera will be, very valuable when shooting moving objects in low light (think indoor sports stadiums).  You’ll be able to use a fast shutter speed (1/500th/sec or faster) to freeze action in its tracks. But your images will have far more digital ‘noise’than the slower, lower ISO would have.

So it’s all about tradeoffs. No free lunch in the ISO world. Is speed or noise your primary concern? You must choose.

Now that I’ve laid out the parameters, I’ll explain how I set ISO in a couple of real-life situations.

When I go out on a landscape shooting trip, I know I’ll be working with lots of long shutter speeds on a tripod.  If there’s any movement in my image, it will probably be some ghostly motion blur that I’m after. I’m not trying to freeze any action but I do want to be able to have the option to make big enlargements of the images. So in this situation I’ll set my ISO for the slowest my camera will allow—in my case, ISO 50. (There’s a custom function on my Canon Mark IV that allows me to boost the ‘low’ end from ISO 100 down to ISO 50.)

'Rip Rap #4, 2011".  Long shutter speeds and tripods allow the use of very slow ISO speeds, in this case, ISO 50. (Copyright 2012 / Andrew Boyd)

‘Rip Rap #4, 2011″. Long shutter speeds and tripods allow the use of very slow ISO speeds, in this case, ISO 50. (Copyright 2012 / Andrew Boyd)

Now let’s say I’m going to shoot an NFL football game in an indoor stadium. My  primary concern will be properly stopping the action on the field. I want a minimum shutter speed of 1/500th sec. – although 1/800th to 1/1000th is much better. I’ll shoot with the aperture on my lens wide open since I want as little distracting in-focus background detail as possible.  A typical exposure for this will be 1/800thsec @ f2.8 or f4, ISO 1200-1600. Even here, I’ll pick the lowest ISO speed that will allow me to achieve my other exposure requirements: in other words, I’ll want to use ISO 1200 over ISO 1600, if there is enough light to allow it.

In a situation like this one, having sufficient shutter speed to stop the action is the top priority. A higher ISO will be required regardless of the increase in digital noise. (Photo by Andrew Boyd / Copyright 2012 The Times-Picayune)

In a situation like this one, having sufficient shutter speed to stop the action is the top priority. A higher ISO will be required regardless of the increase in digital noise. (Photo by Andrew Boyd / Copyright 2012 The Times-Picayune)

These are two extreme examples. Where should you set your ISO for more general photography? Is there a happy medium that you can set that will work fine most of the time and usually give acceptable results?  I’m happy to report there is! For these normal, run-of-the-mill cases, set your ISO on 400 and forget it! (This is the old film speed of black and white Kodak Trix-X film, the workhorse of newspapers and magazines for decades.) You’ll get perfectly useable images with a bit of speed but without too much noise.

That’s really all you need to know. The lower the ISO, the slower you must shoot, but the finer the ‘grain’ in your resulting image. The higher the ISO, the faster you can shoot, but with the tradeoff being increased digital noise in the results. Evaluate what your needs are and set your ISO accordingly.

Hi, I’m Andrew Boyd, a.k.a. The Discerning Photographer, and I hope this post has been interesting and informative. Please leave me a comment about it, let me know what you’d like to see more of on the site! You can also sign up for email delivery of all future articles or my RSS feed. Or subscribe to our Facebook page or our Twitter feed. Thanks!–DiscerningPhotog

Posted in: How To

About the Author:

Photographer, videographer and photo editor. Host and creator of The Discerning Photographer web site. Currently a Canon shooter.

5 Comments on "DSLR Photographers: How to set your camera’s ISO"

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  1. I had wondered about the usefullness of ISO while shooting. So if I understand correctly, a higher ISO lets you shoot faster shutter speeds with lower light?

  2. I am just learning how to use my Cannon Rebel T3, but a friend reccommended that I use it as a backup and obtain a Cannon 40D, or 60D, used as a primary. Can you provide me with a confirmation explanation as to why that is his reccommendation?

    I make a living shooting tourists with live parrots and a nice background then sell the basic sizes of prints and keychains.

  3. Hi Patrick, the 60D is a higher-end camera. But if you’re happy with the results you’re getting, I don’t see a reason to upgrade.

  4. Your understanding is correct, Patrick. The darker it is, the higher the ISO must be at constant aperture and shutter speed. Trial and error is your friend to find out what’s good and to gain experience for the situation. There’s a limit of using ISO, it will add digital noise, which you can determine by false colors and or grainy structure. Just give it a shot and see the results.

  5. David says:

    Yea…In some less-common cases, a higher noise picture is better than a clean one 🙂

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