Chapter 1: Why Canon Speedlights are King

/ L. David Likes Photography/

Rule for adjusting ISO to give you ability to hand hold the camera

Of the program modes, I primarily use Av Mode (Aperture Priority Mode) for portraits. You’ll want to adjust the ISO high enough for the given light on your subject so you can hand hold the camera. Typically you’ll want the shutter speed to be one divided by the lens length (on a full-frame sensor camera). Say the lens length is 100 mm. Then you’ll want to adjust the ISO for that lens to be 1/100 of a second. In this case that would be 1/125 of a second on your camera. Keep in mind with a zoom lens, the requirements for hand holding changes as you zoom the lens! You need to watch that your shutter speed does not go too slow. Best to stay at the same lens length (that gave you high enough shutter speed) and instead of zooming, you move yourself back and forth to get the correct composition.

Other method: Let the Camera determine the correct ISO for hand holding the camera

The other way to determine what ISO to use with your subject for a given f-stop is to set you camera to AUTO ISO. And point the lens at your subject and read what your camera ISO setting shows. Manually set the ISO to this setting as the flash, once turned on, will default to a setting between 100 and 400 ISO. And so if you need 6400 ISO this won’t work. You only need to adjust it manually and you are good to go.

Allow the camera to pick the correct ISO for given f-stop you want by setting the ISO to Auto.

View subject through the viewfinder and read what the camera is suggesting for the ISO to use. In this example it is 6400.

Change the setting from Auto to the ISO the camera was suggesting. Now turn the flash on and get ready to take the picture.