When to Use Fill Flash in Nature Photography
The pop-up flash on your camera can be used to fill in shadows when you need to add just a bit of light when photographing a subject such as a flower. An auxiliary flash unit that goes in the camera hot shoe is a better bet for fill flash. It’s strong enough to send out a beam of light that won’t be interrupted by a long lens.
The pop-up flash won’t work if you’re very close to the object because the lens — especially a long lens — can actually cast a shadow. The shadow is cast on the subject, effectively defeating the purpose of fill flash.
If your flash unit has exposure compensation, you can use this to add exactly the right amount of light to make the image pop. In many instances, you can decrease the amount of flash by just two-thirds EV and get a great image. Some digital SLRs have menus from which you can control the flash output.
Another technique you can try with an auxiliary flash unit — if available — is to manually set the focal length. A flash unit matches the angle of the beam of light the unit emits to the angle of view of the lens. If you can manually set the focal length on the flash unit, you can send a beam that is narrower than the field of view of your lens.
For example, if you’re photographing a nearby object with a 50mm lens, you can set the flash to 80mm to send a pinpoint beam of light to the center of your subject, and create a natural vignette at the edges of the image.
When you photograph several flowers against a colorful background, use camera exposure compensation to decrease the exposure by 2/3 EV. Increase the camera flash exposure by 2/3 EV. The background will be richly saturated because it is underexposed, and the flash causes the flower to be perfectly exposed.