蛋の旅人日誌

昨天晚上試用50D的功能時，發現了400D上沒有的按鈕 — AF-ON
於是上網爬了一下說明，這一查發現還真是不得了，沒想到一顆小按鈕竟可以大幅提升拍攝的流暢度 … (筆記ing)

例如對於高反差場景拍攝人物，傳統的流程 (測光是測背景 / 對焦是對人像 / 用閃燈補人像不足的光) :

對背景測光 > 轉到M模式調成背景的曝光值(調快門或光圈) > 開外閃 > 對人物對焦 + *閃燈曝光鎖(FE-L) > 平移構圖 > 拍攝

改善後流程 : 對背景半按快門(AE-L) > 對人物對焦(AF-ON)+*閃燈曝光鎖(FE-L) > 平移構圖 > 拍攝(全按快門)

當然，還是直接看原廠的說明，可以幫助了解這顆小豆豆上的大大學問 ~ 並且進一步應用到實際情況中！
(Mur Mur … 可以做車就不一定要走路嘛 …)

1. Easier to lock focus

If you are shooting something like a series of portraits of a person, and you want them composed off-center, back-button AF makes it super-easy to take as many pictures as you want. Focus on your subject by pressing the rear button (more on which button later in this article). Once in-focus, take your thumb off the rear button. Re-compose the shot to move your subject off-center. Shoot as many pictures as you like.

With focus activation removed from the shutter button, you now can fire any time you like, and remove your index finger from the shutter button after a shot is taken. No matter what, the camera makes no effort to re-focus when you press the shutter button half-way down again.

If you like to lock focus and re-compose your subjects, you’ll find back-button AF very helpful: Once your focus is set, you can move the camera and take as many shots as you like without AF trying to re-focus on what’s now in the center of your picture.

2. Easier timing of shots

Similar to point number one above, but yet another benefit of pulling focus away from the shutter button is that critical timing becomes simpler to manage. For example, if you were shooting a speaker at a podium, he or she might periodically look up or make a gesture that would be an ideal instant to capture.

If you’ve focused with back-button AF, your index finger is free to shoot at the decisive moment. There are no worries about holding your finger half-way down and waiting, waiting, waiting in that position for your subject to do something interesting.

Even with a very animated subject that may be moving around, you can have your camera’s focus set to AI Servo AF (to track any movement), and just keep your right thumb on the back button to keep focus active, while your index finger can be ready to shoot with no worries about also preserving focus.

3. Less risk of focus errors with moving subjects

For sports photographers and others taking action pictures, back-button AF lets you stop focus whenever something might interfere with the moving subject you’re tracking — without requiring you to stop shooting. In sports, for instance, it’s common for a referee or another player to come between the camera and an athlete being photographed.

With back-button AF, it’s easy to momentarily pull your thumb off the rear button, and you can still keep shooting by pressing the shutter button fully. The camera instantly stops focusing when your thumb comes off the back button. Once the obstruction is out of your way, you can immediately pick-up your primary subject by pressing your thumb on the back button again.

Sports photographers know how common it is for a referee or another player to momentarily step between you and your subject. With back-button AF, it’s easy to keep shooting and halt AF by just pulling your thumb off the rear button until your view is totally clear again.

4. Easier over-riding of AF with full-time manual focus

More than half of Canon’s lenses have a neat feature called full-time manual focus* (FTM). Even if the lens’s AF/MF switch is in the AF position, these lenses allow the shooter to instantly adjust focus manually by simply turning the focus ring on the lens. There’s no need to first move the switch to MF. (喔!? 這麼讚的功能我之前倒沒注意到道說 … )

With back-button AF, this becomes a nearly foolproof feature. Use the autofocus whenever you like by pressing the rear button with your right thumb. Shoot whenever you like by pressing the shutter button. And if you want to touch-up focus, or totally over-ride what the AF is doing, just pull your thumb off the rear button and turn the ring. No matter how many pictures you shoot, pressing the shutter button will not cause the AF to try to kick-in and re-set the focus you just adjusted manually.

5. Easier macro and close-up focusing

Many times, you’ll find that it’s actually easier to get consistently sharp close-up pictures of small objects by pre-focusing, and then moving yourself forward or backward until you see the critical sharp focus appear in your viewfinder. (還真的很 MF 咧 … Orz)

Once again, with back-button AF active, you can use the AF to get within general range (press the rear button with your thumb, then take your thumb off the button), and move a little bit to get things critically sharp. Most important, you can then shoot freely, without AF trying to re-focus each time you touch the shutter button. Finally, touching-up focus with the full-time manual focus feature on certain Canon lenses is simple and quick, and the autofocus never fights you by trying to un-do what you just adjusted.

In close-up photography, it’s often necessary to focus manually, because AF tries to make little changes each time you shoot. With back-button AF, you can concentrate on composition, instead of keeping AF locked in place.