A flash can often be a photographer’s best friend, but it’s also one of the most misunderstood camera accessories.
Unlike natural light (which is continuous) a flash provides a quick burst of light to illuminate a subject. If you don’t understand the basics of how to correctly use a flash your photographs may come out overexposed, underexposed, or with the subject brightly lit while the background is too dark, etc.
To use a camera flash to its fullest potential it’s important to know how the various camera settings affect it. In this tutorial we’re going to take the mystery out using a flash and teach you flash photography lighting basics 101.
First, Understand Exposure Basics
If you understand exposure basics you will probably have more luck with a flash. For instance, your shutter speed will affect the motion blur and exposure of an image. The faster the shutter speed is the less motion blur as it will freeze the action. The aperture will affect the depth of field as well as the exposure and the camera’s ISO setting will effect noise (grain) and exposure. The higher your ISO is set at, the more chance of graininess on your photos.
Distance Matters in Flash Photography
What most photographers who are starting out using a flash don’t know is that the flash of light on most typical cameras is only powerful enough to brighten up an area of about 15 feet. Taking flash photos at a concert or when focusing on a subject or object that’s way out of the flash’s range isn’t going to help you at all.
When illuminating a scene, you generally need four times the amount of light to take shots that are double the distance. For example, if there are subjects at a different distance in your image, such as 10 feet away and 15 feet away, those who are closer will be a full stop brighter when using flash as the primary source of lighting.
Guide Number (GN)
An electronic flash uses a guide number (GN) that relates to the aperture and distance.
The guide number is a combination of the f-stop and the distance to the subject. This will let you know how much light is needed to illuminate your scene. A higher guide number a flash unit has means it can illuminate images at a greater distance.
Two Exposures In One
There are different types of flashes available, such as built-in, hotshoe-mounted, and studio strobe versions.
Each photo you take is basically offering two exposures in one. This will be the ambient light and flash exposures. When the shutter is pressed the flash will fire and the camera will capture both sources of light.
The speed of the shutter won’t have any effect on the exposure of the flash. This means if the shutter is open longer it won’t make a difference since the flash is instant and goes off immediately.
The exposure of the flash as well as its effective range is affected by the ISO and aperture settings, but not the shutter speed. However, the ambient light is indeed affected by the speed of the shutter, meaning you can control this type of light but not the flash.
Digital cameras measure the flash light and ambient light separately. When using the P, AV, and TV mode on your camera, it will try to expose the image correctly for ambient light by setting the aperture shutter speed, or both. The flash won’t affect this unless it’s in the P mode. In this mode, the shutter speed will always be a minimum of 1/60th of a second with the flash. The metering system of the camera can’t predict how much light the flash will provide, so no attempt id made. When the camera is in the manual mode the viewfinder meter measures ambient light only.
If the camera uses any type of automatic flash metering, the light from the flash is measured after you push the shutter button and the output of the flash unit will be adjusted accordingly. This type of flash metering works separately from the ambient light metering and it works by adjusting the flash instead of the exposure settings of the camera.
Well, that’s it for the basics of flash photography lighting 101. We hope you enjoyed this tutorial. Please leave a comment below telling us about your first experiences using a flash.