ISO – Beginner’s Guide to DSLR Photography

June 13, 2012

This is part three of our beginner’s guide to DSLR photography, covering ISO.  In part one, I covered aperture/f-stop and how you can use it to your advantage.  In part two, the conversation shifted to shutter speed and the use of it to show or stop movement.   At the end of this article you should have a pretty good understanding of the three elements the “triangle of light.”


ISO is actually an anagram for the International Organization of Standards.  It is beyond me why it is not IOS, but regardless of that factoid, to photographers, ISO is a standardized system that shows the range of sensitivity to light of camera film.  It has since been adapted to digital sensors on the same scale.  If you really want a more in depth explanation, I suggest going to their website.

ISO Table of Full and Third Stops

ISO Table of Full and Third Stops - CLICK image to see large version.

ISO is often the forgotten side of the light triangle for beginners.  ISO is set up in full stops and thirds.  This differs from the aperture and shutter speeds which will sometimes be represented in half stops.  If you have forgotten what a stop is, a full stop of light is twice as much as the higher setting.  Which in turn, makes it half the light of the next lower setting.  See the chart to the left for full stops and third stops.  Depending on your camera, some of these on the very low side and the very high side may be listed as “LOW” or “HIGH” in your camera instead of the numbers in the chart.

If your image looks too dark and you do not want change the aperture, because you like the depth of field you are getting.  You also like the shutter speed where it is set at to have the right amount of movement, the only thing left to change the exposure of your image is the ISO.  If you took the picture at ISO 200, but it is too dark, you would increase the ISO sensitivity.  You would do this by setting the ISO to a higher number.  So if your image was really dark, you would probably change it from ISO 200 to something like ISO 800.  This is two full stops brighter.  What does two full stops mean to you?  One full stop would be ISO 400.  This is twice as much light hitting the sensor as your current stop, ISO 200.  Then another stop would be twice as much light as the ISO 400, putting you at ISO 800.  So you are doubling the amount of light twice.  This means that your image will be eight times brighter when you change the ISO by two stops.

We know that there is a give and take to each of the other sides of the light triangle.  The same is true about the ISO.  The higher the ISO, the more noise you will notice in your photographs.  Some of you may be wondering what I mean when I say noise.  Without getting too technical for beginners, lets simplify noise as unwanted color and grain.   Basically the higher the ISO number, the noisier the image will be.  Luckily, technology has blessed digital photographers with great sensors and software that allows us to go pretty high in ISO without creating too much of the ill-effects of noise.

ISO 200

ISO 200

ISO 3200

ISO 3200

ISO 3200 With Lightroom 5 Noise Reduction

ISO 3200 With Lightroom 5 Noise Reduction

In the first picture you can see that at ISO 200 the image does not have much noise. That’s because the native ISO on a Nikon is ISO 200. The native ISO of your camera is the default ISO that is recommended for low noise. I am not sure, but I believe on a Canon it is ISO 100. In the second picture, I shot that at ISO 3200. You can clearly see there is more noise, especially in the darker areas of the photo. The last picture is the same image as the second one, but I just bumped up Noise Reduction in Lightroom 5.


The higher ISO’s in today’s cameras offer much more than high ISO films of the past.  So if you are in a lower light situation, do not get scared to set to higher ISOs.  Sometimes the grain can even be useful to set a mood.  This is especially true in black and white images.  It adds a grungy feeling that imparts a definite mood to a photo.  Use it wisely though, imagine the dismay if you shot the first kiss at a wedding at high ISO.  Brides do not tend to like noise in their images.  Hopefully this takes some of the ISO mystery out of your shooting

Taking photos correctly is easy if you know your tools.  The “triangle of light” is the basic toolset for photography.  Once you can control how light is getting on that sensor, everything else is interpretation of a scene.  You could have all of the greatest gear in the world, but if you cannot control the light in the camera, you might as well grab a box of crayolas and a sketchbook.

Now you can piece all three sides of the triangle together.

  • Low aperture numbers or f-stops = more light and less depth of field.
  • Higher aperture numbers or f-stops = less light and more depth of field.
  • Slower shutter speeds  = more light and less control of movement in the frame.
  • Faster shutter speeds = less light and more control of movement in the frame.
  • High ISO numbers = more light and more noise.
  • Low ISO number = less light and less noise.

In the next article, we will apply the knowledge of the “triangle of light” to real life situations and add some recipes to your photography skill-set.  If you still have questions, please leave a comment below.