Backlighting has to be one of my favourite techniques in flower photography. It can be used in many areas of photography but I think it works particularly well with flowers.
Backlighting means that you set up your picture so that the light source (usually the sun but it could be an artificial light source if you are indoors) is behind your subject. This ‘backlight’ can add a sense of passion, drama and atmosphere to your image by making your image, or part of your image, glow and can help separates the subject matter (your flower) from the background.
So what are the advantages of backlighting? Whether your light source is the sun or artificial, the light shines directly through the flower petals or leaves, highlighting their translucence and making them glow. The effect on flowers is ethereal, dramatic and simply beautiful.
Backlighting can be tricky to get right. The light behind your subject can cause all kinds of problems with the exposure of the image. If you are not careful the bright backlight can cause your subject to appear dark and underexposed. If the camera is in 'auto' mode the camera sees the very bright light behind your subject and thinks “wow, way too much light'!! It then tries to fix this by limiting the amount of light that gets into the camera. It does this by either increasing the shutter speed, by making the aperture smaller or by decreasing the ISO as all of these will help reduce the exposure of your image. (See elsewhere on this site for further details about shutter speed, ISO and aperture).
Now, it is not necessarily a bad thing that the camera does these things. In fact, it may well be essential to prevent a horribly overexposed image, but by letting the camera choose the settings you may well not end up with the type of images you were hoping for. By this I am mainly referring to the aperture. A wide aperture is often preferred in flower photography as this will give your photograph a narrow depth of field and a beautifully out of focus background. If your camera automatically chooses to make the aperture smaller to reduce the light hitting the sensor then you will lose this narrow depth of field and your lovely blurred background. For this reason, it is usually best to been in a manual mode or Av mode.
In most instances your light source will be the sun. Therefore, choosing the right time of day is important when it comes to making backlight photography work for you. The best times to photograph back lit flowers is either in the first hour or so after sunrise or in the last couple of hours before sunset. This is because at these times the sun is lower in the sky (making it practically easier to take the photograph) and it casts a warm, gentle light, giving your subject a lovely glow.
Shooting outside during other times of the day is not impossible from a backlighting point of view but it makes it difficult especially closer to midday since the sun is shining directly above the subject, producing a harsh light and unpleasant shadows.
You can of course always bring your flowers in doors. Inside you have a much greater control of the environment in which to take your photographs and you can use a variety of different (moveable) artificial light sources which can be experimented with to your hearts content until you achieve the image you are happy with.
Shooting in manual mode, or in AV mode is important when it comes to creating great backlit flower photographs. Cameras are pretty good getting the exposure correct when the scene is front-lit but, as discussed above, often have trouble metering when the subject is backlight.
The light source is behind the flower and if it is the sun, it is very bright, so the front of your image will be darker than the back. You may well need to experiment with your settings until you get an image that you fell is correctly exposure to your taste.
Take a few test photos, experiment, have fun and adjust your settings to achieve the look that pleases you. Backlighting is great!!