In the days when film cameras dominated the market, multiple exposure images were often created by using several slides to create a ‘slide sandwich’. With digital cameras this has been harder to achieve because once the image is captured it is removed from the sensor, so overlaying two or more frames is difficult. However, the Canon EOS-1D X and EOS 5D Mark III DSLRs both feature multiple exposure stacking of between two and nine frames.
This feature is available for both RAW and JPEG images, though if M-RAW or S-RAW are set the recording quality will automatically switch to RAW. Within the multiple exposure shooting options, there are several exposure settings that can be adjusted to tailor the final output to suit your needs. These are Additive, Average, (Comparative) Bright and (Comparative) Dark.
The Additive exposure control is for those photographers who are used to shooting multiple exposures with film cameras. Instead of taking each image with the correct exposure, the total exposure is added up from each individual image. To achieve the correct result, you should underexpose each image so that the resulting image is correctly exposed once they are all combined together.
The Average setting provides an automatic exposure control whereby each image is automatically underexposed so that the final image is then correctly exposed. Unlike with the Additive setting, all of the images in the multiple exposure will be averaged and taken at the same exposure level setting.
The (Comparative) Bright setting is suited to photographing uniformly dark scenes with bright objects superimposed on top. A classic example of such a scene would be a moon superimposed on a dark night sky – achieving this can only be done by overlaying the bright objects within the scene.
Conversely, (Comparative) Dark is used to eliminate the bright areas of images and so only overlay the dark areas of each image. This setting is useful for eliminating reflections and bright patches in an image – like the reflections you may see when photographing a portrait of someone wearing glasses.