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Flash has to be the most under rated piece of photo equipment on the market. Most people associate flash with taking pictures at night or indoors if the light level is insufficient. Its uses go far beyond these reasons. So much so, flash has evolved into a complete system. Books, DVD’s and workshops are specifically devoted to the topic. A technique I’ve incorporated into my flash repertoire is to put my camera in manual-metering mode, set a specific shutter speed and aperture, attach a flash to the hot-shoe, and let the camera and flash technology provide me with perfect exposures.
Step 1: Select Manual-metering mode on your camera. In manual mode, you determine the aperture and shutter speed at which the photo is made. In the two accompanying photos, one has a brighter sky background. I made an exact image in Aperture priority with my lens set to ƒ/16. The corresponding shutter speed was 1/30th. It resulted in the bright sky background. I switched to manual mode, set the shutter to 1/30th and kept the aperture to f16 and made the image shown here.
Step 2: I wanted to tone down the bright sky spots as I found them very distracting. I accomplished this by setting my shutter speed to 1/125 of a second. In essence, I underexposed the background by two stops from the original image made at 1/30th. Manual mode enabled me to do this as the shutter speed and aperture work
independently. Note that the amount of light on the flower in both images is identical. The beauty of today’s technology is the flash output is automatically determined by the aperture to which the lens is set. Even in Manual mode, the amount of flash is calculated automatically.
The reason this works is the shutter regulates how long the camera’s sensor sees the light. The aperture dictates the amount of light the flash puts out. In that I kept the aperture constant in the two exposures, the flash output remained the same. In that I changed the shutter speed from 1/30th to 1/125th, I created a two-stop differential in how long the sensor saw the ambient light. This resulted in the darker background. The same effect could be achieved in Aperture priority by dialing in two stops underexposure, but depending on your custom settings, you’d also dial down the power on the flash. Rather than change my custom settings, I find it far easier to go into Manual mode and let it rip.