How To Choose the Right ISO Settings When Shooting With Flash

It’s no secret that we’re big champions of using lighting here at The Phoblographer. Obviously, natural light can produce excellent results. However, there’s no denying that the use of flashes provides significantly more control. It also allows us to create reliable results repeatedly. While lighting may seem daunting to photographers new to the world of on/off-camera flashes, the key to success lies in understanding the fundamentals. We’ve previously covered the use of flashes in general. Today, we’ll be focusing specifically on ISO settings in relation to shooting with flashes.

A Refresher on ISO?

What exactly is ISO? We’ve discussed this in detail previously in one of our beginner’s guides:

“ISO colloquially refers to the international standard used to measure a camera’s light sensitivity. The higher the ISO value, the more light-sensitive a camera is.”

excerpt from our Guide to the Top 10 Photography Terms for Beginners

ISO is part of the trio that makes up the Exposure Triangle, a foundational principle of photography. (Be sure to check out our Beginner’s Guide to the Exposure Triangle for more details.) Setting your camera at the appropriate ISO setting is a fundamental step in creating a well-exposed image.

Your Camera’s Base ISO Isn’t Always the Best Way to Go

Your camera’s base ISO value will generally produce images with the least amount of digital noise. Depending on your specific camera, this is usually ISO 100 or ISO 200. While the base ISO value is often a good place to start, it may not always produce the intended results when you’re balancing your flash against ambient light. While this may seem confusing and counterintuitive, it’s not that challenging once you understanding the relationship between your camera’s sensitivity and your surroundings. It’s all about balance.

While you’re shooting with flash, a good principle to remember when selecting your ISO value is to determine how you want your entire scene to look. Start by focusing on the background first. Dial in your ISO value so that your camera produces an image with the background you desire. Once your desired background is properly exposed and locked in, add flash to illuminate your subject. The rest is simply a measure of balancing your flash’s light output with the ambient light. Think of it like you’re cooking a meal. ISO is the recipe that dictates the number of ingredients you’ll need for any particular dish. Flash would be the seasoning that highlights the main ingredient to help it stand out.

If you’re shooting outdoors in a brightly lit environment, start at ISO 100. Be sure to also adjust your aperture and shutter speed accordingly so that your background is properly exposed. A blown-out background tells us nothing about the scene. Once you’ve dialed things in, add in light from your flash to fill in the harsh shadows cast by the sun.

As your shooting environment changes, you’ll want to adjust your ISO value accordingly. If you’re shooting outdoors during the twilight hours, or if you happen to be photographing in open shade or reasonably lit indoor areas, consider raising your camera to around ISO 400. While raising your camera’s ISO value can in fact lead to noise appearing in your image, do not be alarmed. Most leading modern digital cameras today can produce excellent results with negligible noise when shooting up to ISO 3200 or even ISO 6400. When photographing in low light scenarios, consider ramping your camera up to ISO 800 or 1600 (or even further if necessary). Rather than the rest of the scene falling into pitch-black darkness, the higher sensitivity will allow your camera to pick up what’s in the background. Simply add the appropriate amount of flash needed to light your subject and you’ll be rewarded with an image where both the subject and the surroundings appear properly exposed. Don’t let the numbers throw you off. Once you get accustomed to using the appropriate ISO value when shooting with flash, it’s like riding a bike.