Stopped down metering with Canon EOS and older FD lenses

With EF Lens and camera in Av mode

  1.     Compose shot
  2.     Focus
  3.     Meter
  4.     Shoot

With EF lenses, the camera controls the exposure settings so there’s no need to stop down the lens before metering.  The firmware will take the desired aperture setting (and optionally ISO speed) into account when metering, then tell the lens to stop down to the desired aperture setting as part of the shooting sequence (stop down, move mirror, release shutter, read sensor, close shutter, release mirror, release aperture).  In Tv, M, and P modes, the same is true but in Tv, you set the shutter speed manually and the camera picks an aperture setting during metering instead of the other way ’round.  In Programmed, it picks the best settings based on available light and distance to focal target.  In Manual, you set everything and the camera only whitebalances during metering (unless you also have that set to manual).

With FD lens and camera in Av mode, focus first

  1.     Compose shot
  2.     Focus
  3.     Stop down
  4.     Meter
  5.     Shoot

Since the camera cannot communicate with the older FD lenses, you have to stop down manually.  This isn’t as bad as it sounds.  You still set the desired f-stop during composition (using the lens’ aperture ring instead of the camera’s aperture setting) but leave the aperture ring on the adaptor in the “open” setting.  After you focus the shot through a wide open aperture, then stop down using the adaptor ring and meter the shot.  After shooting, return the aperture to the open setting to compose the next shot.  It’s not possible to use Programmed or Tv (shutter priority) modes with FD lenses since the camera cannot tell the lens what aperture setting to use.

With FD lens and camera in Av mode, meter first

  1. Compose shot
  2. Stop down
  3. Meter
  4. Hold exposure
  5. Release aperture
  6. Focus
  7. Stop down
  8. Shoot

For moving objects or low-light shooting, it may be advantageous to meter the shot before focusing.  This is more involved; the aperture still needs to be stopped down before metering.  That’s what the Hold Exposure button is for.  Stop down, meter, hold exposure, release the aperture, then focus, stop down again, and shoot.  The advantages to this method are not universally acknowledged but some experts say it’s the better shooting model and allows for more accurate focus.

Of course, if you’re using a low f-stop and are confident in your shooting, you can easily focus through a stopped-down aperture.  That’s even easier but probably less accurate than the other methods.


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