Sheila White Guevin Photographer | ISO - Part one of the BIG THREE

ISO - Part one of the BIG THREE

February 07, 2015  •  Leave a Comment


The Big Three

Part One: ISO

This is a three-part look at ISO, shutter speed and aperture. If you are ready to move past the automatic settings and take control of your camera, you will need a basic working knowledge of these three variables.

For a more in-depth look, the Internet is a great resource for free articles and videos.

Digital ISO and film ISO have a strong correlation. So if you remember how film ISO worked, you will easily move to digital ISO. 

To select ISO for film cameras you needed to know the light of your shooting conditions. Film boxes often came with a chart for picking the right ISO.

ISO 100 was for very bright sunny days and studio lights.

 ISO 200 was for mostly sunny daylight to partially cloudy.

 ISO 400 was a versatile film geared for cloudy days, but one that could create acceptable photos on sunny days by using a faster shutter speed and in dimmer situations by using a slower shutter speed and a flash. ISO 400 was an all-around film for mixed light.

ISO 800 was the choice for inside and on-camera flash.

Back when Kodachrome was more than a Paul Simon song, photographers chose the film ISO according to the conditions under which they expected to be shooting.  While ISO of 400 was the most versatile, it did not produce the best results in all situations.  ISO choice had a direct effect on the quality of your photos.

Film ISO basics were the lower the number, the more light you needed or less sensitive the film was. The higher the ISO, the less light you needed and the more sensitive the film was. Low light film and conditions produced readable photos, but that often came with a grainy look.

Digital ISO has a similar light chart.  An ISO of 100 requires that a lot of light get to the sensor. If I push the ISO to 25,600 (and yes, you read that right, which makes it 256 times more sensitive than a 100 ISO) I can get a readable image in a barely lit situation, however, this ability comes with “noise.” Both grain and noise are undesirable side effects from shooting in less than ideal conditions.

Unlike film, the sensor does not become more sensitive to light as the ISO increases. Instead, the camera digitally increases the color signature for each cell or individual sensor.

The other huge advantage of digital is that you can change the ISO for each individual shot.  This is great for when your lighting conditions are constantly changing from outside, to bright light, to inside and more.

Take a look at ISO 100: Imagine a perfect sunny day at the beach, where the colors are beautiful and vibrant, the sensor registers variations of the three color bands(red, blue and green) on each pixel sensor at around 85%. Now, on that same beach on a very cloudy day, the sensor sees the same scene but registers the colors at only 10%. If printed at 10% the photo would be dark and lacking in resolution. 

One option on our gray day is to change the ISO from 100 to 800. This increases the value of our registered color from 10% to 8 times higher at 80%. This virtually allows the camera to register more light as a color signature.

The downside of increasing the ISO is that the sensor may also register electronic waves as a version of light. This is called “noise.” So when I push up the sensor reading to be 8 times more sensitive, my other readings are 8 times more sensitive. This means the noise that was not visible on my sensor at 100 ISO is now 8 times stronger.

Sensors are categorized both by pixels and size. As a rule, the bigger the sensor, the bigger the pixels. These larger sensors register a lower amount of noise and a higher dynamic range. Newer generation sensors are less sensitive to noise and this is why many of the expensive full frame sensor cameras give you a cleaner photo with less noise at the lower light levels.

Shooting on automatic, the camera makes choices in an attempt to give you the best quality photo by balancing the ISO, shutter speed and aperture.  But the choice is purely a hypothetical game of math for the camera and this becomes obvious when the wrong object is in focus or perfectly exposed.

Artistic control in the digital world, always starts with technical knowledge.

Tomorrow, we will continue this journey by taking a technical glimpse at shutter speed.

Assignment One:

Pick a location where you can spend 15-20 minutes shooting.   Select “P” for program. If you don’t know how to select a feature on your camera and move around the different settings this is a good time to get out your manual or check on the Internet.

Using the existing light at the location -  take a photo at ISO 100 and then take the same photo at ISO 200 and keep going higher till you have a set of photos at each ISO. The camera will modify the other two from the BIG THREE so all your photos should be readable.

Upload your photos to your computer and notice the differences. This is a visual art. It is all about seeing the results of the camera you shoot.


Note: There are two things you may have put away when you got the camera out of the box. One is the user guide or manual; the other is the lens hood. This is a good time to go get both. Even when you can switch easily among the settings, it is always a good idea to have your user guide around when you need it. And as you learn the technical aspects of your camera – you are going to need it.


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