ISO...Finding the Light

Everything You Need to Know About the Camera Setting - ISO

When we discuss shooting in manual, everything ultimately comes back to the three most important settings: aperture, shutter speed and ISO. ISO will most likely be the easiest camera setting that you will experiment with. So what is ISO?

The ISO speed is a measure of how sensitive the sensor of your camera is to light. A lower number is less sensitive, and a higher number is more sensitive. The term originated in film photography, where film of different sensitivities could be used depending on the shooting conditions, and it is no different in digital photography.

The ISO sensitivity is represented numerically from ISO 100 (low sensitivity) up to ISO 6400 (high sensitivity) and beyond, and controls the amount of light required by the sensor to achieve a given exposure.

To understand this, let’s look at two different situations:


Photos taken with a slower ISO speed will have less noise (speckled grain-look) than ones taken with a faster ISO speed.

If shooting outside on a bright sunny day there is a lot of available light that will hit the sensor during an exposure, meaning that the sensor does not need to be very sensitive in order to achieve a correct exposure. Therefore, you could use a low ISO number, such as ISO 100 or 200. This will give you images of the highest quality, with very little grain (or noise).

The unedited photo to the left was taken in our studio with an ISO of 200. I was also using studio lighting, which helped project enough light on Vivian. If I hadn't used those lights, the room would have been too dark and I would have had to have used a much higher ISO setting.


If shooting in low light conditions, such as inside a dark museum or at a wedding reception, there will not be much light available for your camera sensor. A high ISO number, such as ISO 3200, will increase the sensitivity of the sensor, effectively multiplying the small amount of available light to give you a correctly exposed image.

The image to the right was taken with our studio lights off, at the same ISO of 200. You can see now how dark the image is.

Whether you are using a window, the sun, an external flash or studio lighting, a good light source is imperative to achieving a good quality photo.

Raising the ISO comes with an unwanted side effect of increased noise on the image, which looks like a fine grain, reducing the overall image quality. The noise will be most pronounced in the darker/shadow regions.

The photo below shows a zoomed in clip of a photo taken in the same studio, still with the lights off, but with an ISO of 6400. You can now see that unwanted noise that has occurred due to not having an adequate light source and using a high ISO.

The overall goal when it comes to ISO is to keep the number as low as possible. Because as we discussed, the lower the ISO, the less noise and the higher the quality of the resulting image.

Outside on a sunny day, try selecting an ISO of 100 as a starting point. If it clouds over, try selecting an ISO between 400-800. If you move indoors, consider an ISO of around 1600 or above. If you are near a quality light source such as a window, that setting may be lower. Remember, these are approximate starting points.

The visual below will give you a better understanding of how to calculate ISO.

If you are still having trouble with the concept of ISO, check out the video below where I explain ISO a little more and show how it affects each photo taken.

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