Re: Problème de vitesse d'opturation..
par
aleksong
» Jeudi 02 Décembre 2010 22:43
Si tu n'es pas allergique à l'Anglais:
LOCKING EXPOSURES AND/OR FOCUS
Auto exposures change as you point the camera around the environment. But the environment is usually a place with a fixed light level that includes areas of greater or lesser lighting.
If you wish to shoot images that capture every part of the environment at the same exposure, you can use Manual Exposure mode, or you can take your cameraʼs exposure and/or focus advice and lock the exposure and/or exposure (or even flash intensity) with the AE-L/AF-L button.
You have no less than seven options there. They all start with using the AE-L/AF-L button on the camera back just to the right of the viewfinder.
For most functions, when this button is pressed and held, exposure and/or focus can be temporarily locked, preventing them from changing until the button is let go. Depending on menu choices (CSM #15) :
AE/AF Lock. Both are locked together at the current focus position and the immediate exposure at the time the AE-L/AF-L button is pressed. The camera can be moved to new framing with exposure and focus unchanged. You must hold the button down or lose the focus and exposure settings, returning
them to other AF and AE options you have set elsewhere (CSM #02, CSM #16).
i The default is to have this button hold both AE and AF, locking them together. You may press the AE-L/AF-L button after half-pressing the shutter button to lock exposure at that instant and the current auto-focus setting. This is good for quick panoramics in which maintaining focus and exposure is necessary. Make sure you donʼt touch the zoom between sequence frames.
i Keeping the AE-L/AF-L button pressed will continue to hold both settings through more than one photo. The only question is how long can you continue to keep the button pressed. By electing to use the shutter half-press to lock one of these ideas, you can leave the other one to your thumb.
i Any change of focus will cause slight image size changes in the results, so shooting a panoramic for stitching several images together should be done with exposure and focus locked. If you have time, switch to Manual exposure mode and switch the lens to Manual focus.
AE Lock Only. The exposure alone is locked at the moment the button is pressed while focus is handled normally.
AF Lock Only. Either AF focus mode (CSM #02) is locked at its current position while exposure is computed at the moment of shutter press. You may wish to use the shutter half-press to achieve focus before you lock it with the AE-L/AF-L button.
AE Hold. The exposure will be computed and locked the instant the AE-L/AF-L button is pressed and it will be held as long as the camera meter stays awake (CSM #23) without continuing to hold the AE-L/AF-L button down. A second press of the AE-L/AF-L button will cancel the lock.
AF-ON. The AE-L/AF-L button causes the auto-focus to find focus in the manner of your AF preference (CSM #02), either locking it if AF-S is used, or continuously following focus if AF-C is used. Use with care. This mode has some unusual side effects that can confuse you:
i Warning: When AF-S is selected, the AF-On setting (CSM #15) sets and locks auto exposure requiring you to hold the AE-L/AF-L button down during the shot. If you leave the camera in this mode, the next time you pick it up, you will wonder why the camera is not releasing the shutter. It may appear to suddenly be broken.
i It gets worse—if you have the camera set for AF-C (CSM #02), and donʼt press the AE-L/AF-L button before exposure, the camera will fail to auto-focus entirely, but the shutter
will trip, exposing an image that probably is out of focus. With AF-ON the camera is looking to the AE-L/AF-L button instead of the Shutter Release for its cue to auto-focus. If you use AF-ON, switch it off when you are through.
FV Lock. As soon as you press the AE-L/AF-L button, the camera fires a test flash and computes an exposure solution. Subsequent images are all shot with the same flash energy even if your subject changes position, shape, distance or tonality for any reason. A second press dismisses the lock so normal TTL shots occur. A third press makes a new test flash.
i One useful strategy is to use the option to cause the AE-L/AF-L button to only lock focus when it is pressed (AF Lock Only in CSM #15) with the AF-C setting (CSM #02). You have just told the camera to focus continuously unless you lock the current focus point with the AE-L/AF-L button.