I is for ISO

In our very first post, A is for Aperture, we noted that the three basic elements of the triumvirate of photography are aperture, shutter speed, and ISO and these elements are our tools to create a good exposure.

ISO is a measure of the sensitivity of the light sensor in our digital camera. A low number, like 100, means low-sensitivity, and a high number, like 3200 means high sensitivity. Generally speaking the lower the ISO, the better the quality of the image will be because with increase sensitivity comes increased noise. What is noise? It's a graininess in the image introduced in increasing amounts as the ISO is cranked up. These two images don't look terribly different at first, until you zoom in ... see the noise in the ISO 3200 image?

ISO 100, Aperture f/11, Shutter Speed 1/1.6 sec 

ISO 3200, Aperture f/11, Shutter Speed 1/50 second

ISO 100 and slow shutter speed (1/1.6 second) at f/11

ISO 3200 at faster shutter speed (1/50 second) at f/11

So as a general rule shoot at the lowest ISO possible. You might ask if the lowest is the best, why would you change it at all and the answer is circumstances. For example, shooting early one slightly breezy morning I saw this great red barn out beyond a huge field of bright yellow mustard flowers and I just had to capture that image.

ISO 400, Aperture f/20, Shutter speed 1/80 second

I wanted most of the image in focus, so I set the camera to Aperture Priority and I set the aperture to f/20. At an ISO of 100, the camera set the shutter speed well below the 1/60 second I felt comfortable with - handheld. Even at ISO 200 the shutter speed was still too slow to feel confident of a shake-less handheld image, so I set the ISO to 400, the shutter speed came in at 1/80 second, and this is the result. This is how the triumvirate works together - give and take to get a good exposure.

Let's try a weekend project: Get To Know Your ISO. We all have different cameras and they will perform at higher ISOs differently. For example, on my first camera, the Nikon D60, I found through experience that I could comfortably take pictures up to ISO 400 without undue ugly noise, take some pictures at ISO 800 but at ISO 1600 images had too much grain to be any good. Test your camera this weekend and let us know how high you can go without too much noise. Post your results in the comment section here to share your gear's performance. We all need to understand not only the capabilities of our cameras but also their limitations, so we can use them effectively. I look forward to reading your results.

 

Comments

[Nancy Lanzoni]

Despite the gray day, I went to the beach this afternoon around 4pm. I was surprised that there were many more interesting photo opportunities than I thought there would be. I set my Nikon D60 at ISO200 and 1600 for each picture I took. the photos taken at ISO200 had much more visual interest, especially with some of the shots with water in the foreground. The wave detail was much better with the lower ISO. The only time that ISO1600 was useful was when I got close enough to some of the seagulls that were coasting along in the wind.

[Claudia]

Nancy, I'm so glad you still went out despite the gray day. I would love to see some of the pictures you took. Do you share photos on Facebook or better yet on Google+ (it's free and we add each other to our circles). I like the way you approached your shoot - ISO 200 and ISO 1600. When you zoomed in on the 1600s did you notice more noise than when you shot on 200?