Tuesday, 27 November 2012

Back Button Focusing

Most amateur photographers often retort to constantly switching between focus modes and also turning the AF button ON and OFF to adapt to different shooting conditions. However there is one solution that would allow you to achieve the best of both worlds namely One Shot and AI Servo by setting your cameras focus and shutter functions to two different buttons. Let us discuss a little about what is back button focusing and also what purpose does it serve.

Back Button Focus
Back Buton Focus in Canon and Nikon Cameras

What exactly is Back Button Focusing?

By default the focusing and shutter functions are set to the shutter release button. Focusing is activated by half pressing the shutter release button and the shutter is triggered when the button is pressed fully. By setting your camera to back button focusing what you essentially do is to disable the focus function from the shutter release button and assign the function to another button situated at the back of your camera which could be operated by your right hand thumb.

What are the advantages of using Back Button to Focus?

Back button AF as it is often referred to by professional photographers makes AF functions more effective in certain situations. However whether it is suited for you is entirely dependent on your shooting style, the kind of subjects you shoot, focusing mode used, and also your AF drive method namely single mode or servo mode.

Let us discuss some of the advantages of using back button focusing.

Lets you use AI Servo Mode for all Situations

With focus function removed from the shutter release button you could now use AI Servo Mode for all your shooting situations. It is also much easier to lock focus and keep it that way; once you attain focus, just remove your thumb from the AF ON button and focus remains locked, you are now free to recompose your shot and take as many pictures as you want without the camera shifting focus every time you press the shutter.

No Need to Shift the Lens to Manual Focus Mode

Many times photographers are faced with tricky situations that confuse the camera and so the AF function struggles to achieve focus. Also there are situations when the photographer would like to lock focus at a particular point. In these kinds of situations the most common solution adopted by photographers is to switch the lens to manual focus mode. However by using back button focusing there is no need to switch the lens to MF as you are free to focus the lens manually and once you attain focus; if you do not press the AF ON button the focus stays locked.

Most pro grade Canon lenses have a feature called full-time manual focus. The advantage of these lenses is that 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. When combined with back button focusing you need not bother to switch your lens to MF any more, you can always stay in AF.

Better Timing of Shots

Back button focusing allows you to better time your shots. Imagine a situation in which you would like to shoot a stationary subject but at precise moments, ordinarily what you should do is to attain focus, keep your shutter button half pressed to lock focus and keep it that way till the moment arrives. And once you take a shot the camera again should attain focus to click again. Setting focus independently of shutter allows you to lock focus and keep taking pictures at precise moments to capture various expressions, gestures, poses etc. even if the subject shifts position you could easily refocus by gently tapping the AF ON button with your thumb.

Lets You Track Moving Subjects Better

For people who shoot action like sports and wildlife photographers, back button focusing is helpful to track the moving subjects in AI Servo Mode and if the subject suddenly stops the photographer could immediately lock focus by taking his /her thumb off the AF ON button and recompose the frame as required. He/she is free to further fine tune the focus manually if needed without the need to shift the lens to MF mode.

Makes Focusing Easier for Macro Photography

Back button focusing could be a boon for macro photographers. When enabled it allows photographers to quickly attain focus by pressing the AF ON button and then attain precise focus by moving the camera forward and backward until you achieve critical focus. Once focus is achieved you are free to take as many shots as required as the camera does not interfere by trying to re-focus. No more shooting in full MF or shifting from AF to MF once focus is achieved.

Back Button Focus in Canon Cameras

Canon was the first camera manufacturer to incorporate this feature in their cameras in the late 1980s. It was done in response to the demands of sports photographers for some way to start and stop AF without interfering with continuous shooting and almost every DSLR from the canon range has this feature built in. Some advanced cameras from Canon even have a dedicated AF ON button in addition to the AE Lock button (indicated by an asterisk symbol) and as per the users convenience the functions of these two buttons could be interchanged by a custom setting.Refer your cameras user manual to find out how to set back button focus on your camera.

Back Button Focus in Nikon Cameras

In case of Nikon cameras you use the AE-L, AF-L buttons for back button focusing. Follow to guidelines given in your camera user manual to find out how.

Before you actually activate the function go through the user manual and understand what each of the options available does and find out which one will suit your purpose best. Most commonly given options are :-

1. Metering + AF start

Camera default setting – both buttons (shutter & AF ON perform the same functions)

2. Metering + AF start / AF stop

Focus is controlled by shutter button but you could lock focus anytime by pressing the AF ON button.

3. Metering start / Meter + AF start

Focus is activated by AF ON button and not by shutter. Camera takes fresh metering for each shot.

4. AE Lock / Metering + AF start

Focus is activated by AF ON button and not by shutter. If the shutter button is kept half pressed metering is locked and would not change until you release the shutter button.

5. Metering + AF start / Disable

Functions just like the default setting except for the fact that AF – ON button is disabled. This setting is for those photographers who are worried about accidentally pressing the AF ON button.

Option 1 given above is the default setting. A little bit of experimenting with the rest 4 options will help you find the one which suits your needs. It should be remembered that it would take a little time for you to get used to it. So make sure you have familiarized enough with the new settings before you shoot any important event. Of course you could cancel the settings and put your camera back to default settings at any time by using the clear all custom functions option.

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