Light Loss in Macro and Close-Up Photography
Light loss occurs in macro and close-up photography because the lens is so far from the digital sensor in order to achieve focus at close ranges. The image produced by the lens (known as the circle of illumination) becomes larger than usual and is spread out beyond the borders of the sensor.
Light that falls outside the surface of the digital sensor is lost, and so less light is used in making the exposure. The figure shows a diagram of how an ordinary lens directs light to the camera’s digital sensor, and how a macro lens does the same.
If you were to expose the photograph exactly the same using each camera in the diagram, then the photograph created with the macro lens would appear darker than that of the ordinary lens, due to the loss of light.
The more your subject is magnified (the closer you get to it) the greater your light loss. A 1:1 ratio can cause about 2 stops of light loss, but you need to read your lens’s manual to have an accurate idea of how much light loss you’re dealing with.
To compensate for light loss, adjust your exposure settings to brighten your exposure. Use one of these methods, or use some combination of them:
Opening up your aperture (the setting that determines the rate of light entering your lens during an exposure) lets in more light and can compensate for light loss.
If you want to work with a shallow depth of field, opening up is your best option. But if you wish to use a great depth of field in order to maximize sharp detail in a scene, then you have to keep your aperture closed down as much as possible.
Slowing down your shutter speed is a valid way to compensate for light loss when you’re photographing a still subject and don’t have to worry about the wind. If there is any movement at all in your scene then you want to shoot with the fastest shutter speed possible.
Raising your DSLR’s ISO setting is great because it doesn’t affect your depth of field or the length of your exposure. It causes more digital noise to appear in your images; if you raise it too high, your image quality starts to diminish.
Try testing your camera by shooting at the lowest ISO level, going up one stop at a time all the way to the highest level and comparing the results on your computer monitor.
Use a combination of aperture, shutter speed, and ISO settings in order to minimize how much each is affected by compensating for light loss.
Adding light to your scene is a great option because you can choose the specific exposure setting that works best for your situation and control the exposure by controlling the light.