Canon EF 24-70mm f/4L IS USM User Manual - Page 12

7. Exposure during Close-up Shooting Setting the Exposure When taking photographs using TTL metering, no exposure compensation is necessary to meter the light coming through the lens. With TTL metering, AE (autoexposure) is possible at all focusing distances. Just set the desired picture-taking mode, then check the shutter speed and aperture before taking the picture. Magnification and Effective f-number The aperture displayed by the camera assumes that the focus is set to infinity. The actual aperture (effective f-number) becomes darker (effective f-number increases) at closer focusing distances (magnification increases). This does not cause exposure problems for normal picturetaking. However, for closeup photography, you cannot ignore the change in the effective f-number. When you use a handheld exposure meter to set the exposure, you must take into account the exposure factor shown in the following table. Magnification Effective f/No. Exposure Factor (stops)* 1 : 5 4.71 +1/3 +1/2 1 : 3 5.06 +2/3 +1/2 1 : 2 5.66 +1 +1 1 : 1.5 5.66 +1 +1 * Upper values: 1/3 stops. Lower values: 1/2 stops. ●● The correct exposure for a close-up shot largely depends on the subject. Therefore, try to bracket the exposure for the same subject. ●● Using aperture-priority AE (Av) or Manual (M) picture-taking modes are recommended for macro photography as it is easy to adjust depth of field and exposure in these modes. ENG-11