For the measurement to be active in any of the Canon EOS cameras, it must be initiated by one of several actions:
- Half press of the trigger.
- One press of the AE-L button (automatic exposure lock)
- One press of the AF-ON button (auto focus activated) (if the camera is equipped)
- A press of any other button assigned by the custom control menu to start the measurement
Once the measurement has been started, the time that remains active is also determined by several user selectable settings and if one is using the viewer or the live view.
- In certain measurement modes, such as & # 39; Evaluative & # 39 ;, exposure is generally blocked after the initial measurement as long as the shutter button is held down when in an automatic or semi-automatic exposure mode.
- In other measurement modes, such as measurement & # 39; Center-weighted metering & # 39 ;, & # 39; Partial & # 39; or & # 39; Spot & # 39;, the measurement will remain active and continue to update until the shutter button is fully pressed (or the measurement is turned off). The exposure is not set until just before taking the picture (with the exception of the exposure mode & # 39; Manual & # 39; complete).
- The measurement will remain active while you press one of the buttons mentioned above, take the picture or release the buttons and the measurement "run out".
- Some Canon cameras allow the time measurement to remain active after the shutter button is no longer pressed so the user can select it. Others do not offer this custom function and the measurement "turns off" in approximately four (4) seconds after the shutter button (or other button mentioned above) is no longer pressed.
- There is a separate configuration for the duration of the active measurement in Live View. The options for several of my Canon cameras include 4 seconds, 16 seconds, 30 seconds, one minute, ten minutes and 30 minutes.