There are two options to further increase your control over the kind of focus the camera uses.
In the A700/A900 there is a button in the back of the camera, next to the AEL button thats labeled AF/MF.
This button allows you to easily change between AF and MF without doing anything else with the lever.
If the lever is set to S, A or C, pressing this button will change from AF to MF. If the lever is set to MF, when you press the button, the focus will change to AF-S mode.
This is an extremely useful button, why?, because if your camera doesnt focus what you want due to confusion or the lens takes too long to focus at all, you can IMMEDIATLY switch to Manual Focus and do the job yourself, instead of reaching out to a lever placed below the lens release button, you can switch the focusing style without taking the eye from the viewfinder.
I believe Sony kept this button just for the A700/900 due to the fact that usually advanced or professional users will be the ones switching from AF to MF and viceversa more frequently than amateurs or beginners. This is just my personal opinion.
Now, there is something about this button that you should know to determine which option suits you best.
The default setting for this button requires for you to HOLD the button in order to work. In other words, if you are shooting in AF and want to go to MF, you got to press the button AND keep it pressed in order for the camera to remain in MF, because as soon as you take your finger off the button, it goes back to AF.
Personally, I find this setting really annoying, because if I got to do a careful movement of the focusing ring and I got to worry also about keeping the button pressed, it just takes some of my attention and places it on the button. Not to mention that if Im pressing the button and my hands move for whatever reason, the focus goes back to AF and I still think its on MF. I can notice if this happened because the focusing ring gets stiff and not lose as it would be in MF, but if someone else doesnt notice the change, it can force the focusing ring, which can lead to breaking the lens internally and ruining it.
Of course, that is just my opinion, there will be some people who feel a lot more comfortable with holding the button and thats completely ok. The camera is designed to be customized to the user's wishes, not someone else's.
However, for those of us who dont like the idea of holding while focusing and rather press and forget, Sony also thought of the option to TOGGLE with this button.
When you set the button to Toggle, you need to press it once to change from AF to MF, the camera will remain in that mode until you press again the button, which will switch it back to the original focusing mode (either AF or MF, depending on where the lever is set).
To change the AF/MF setting: Menu->Custom (the tab with the clockwork icon) Menu 1-> AF/MF control->Toggle.
If you change your mind later, follow the same instructions but pick Hold instead of Toggle.
If the location of the button doesnt suit you but you still want another button to work as the AF/MF button, you can always use the C(ustom) button.
To set the C button to work as the AF/MF button, go to: Menu-> Recording (the tab with the camera icon) Menu 1-> Custom Button->With the joystick (Multi selector) choose AF/MF control and press the joystick to set it.
If you browsed through the Menu pages or the camera manual, you may have seen a function called DMF.
DMF stands for Direct Manual Focus. DMF is a cross between AF and MF.
When DMF is enabled, the camera will focus using AF, but once it has achieved focus, it will release the focusing ring for you to move it if you decide to do so. It will remain in MF until you half press the shutter again, which will prompt the camera to focus in AF and then go to MF.
This is an useful function if you want to have the MF function enabled without having to press the AF/MF button (these cameras give you plenty of choice, dont they? :-) ). This would be like those gearboxes in cars that allow you to switch between manual and automatic. Cool eh?
DMF can only configured using the AF-A mode. You cant use it if the lever is set to something else than AF-A.
To set DMF, go to: Menu->Recording (camera icon) Menu 3->AF-A Setup->DMF
Now everytime you have the lever on AF-A, the camera will go to DMF.
Both the button AF/MF and DMF give you direct and quick access to either AF or MF or both. These two functions are of great value when you shoot in circumstances where you need to switch between both modes frequently. Remember I said it'd pay off to learn about Manual Focus? These two functions make it a lot easier for you to work with MF.
And with this we conclude our series about Focusing Modes. I hope it was of some help to you, go out and test all the settings, determine which one suits you better and keep shooting!
Until next time.