Nikon cameras (and most certainly others as well) has a button on the back side of the camera called AE-L / AF-L. The normal function of this button is to lock exposure and auto-focus so that you may recompose the shot and then press the shutter release without the camera attempting a new focus or metering and changing the exposure parameters.
This article will start off on the D70s camera that I have, but should work very similar on most Nikon digital bodies. It may also be the same for Canon and other brands although I have not verified it. If you know, please leave a comment to this effect!
Most people are probably aware that in the camera CSM menu item #15 you can control what this button actually does. The obvious choices here are the following:
- Lock exposure and auto-focus at the same time (AF/AE mode)
- Lock only auto-focus (AF mode)
- Lock only exposure (AE mode)
What people generally do not know is that there are two more modes that are very useful in certain situations. These modes are:
- Auto focus ON mode (AF-ON mode)
- Flash metering off mode (FV mode)
They are not so well described in the manual and so you may want to practice a bit with using them! The rest of this article is to describe some situations where they are quite useful:
This moves the autofocus from the half-way pressed shutter release button to the AE-L/AF-L button on the back side of the camera. Why do you want that?
There are several situations when this is handy. If you have pre-focused the camera and don’t want it to change focus you can prefocus with the AE-L/AF-L button and then keep pressing the shutter release. If you press it half-way the camera will meter but not refocus.
In the menu this is called AF-ON (auto focus ON).
With lenses that have VR (vibration reduction) pressing the shutter half-way engages the VR function (when it is turned on). This function draws lots of juice from the camera battery so it is a good thing to not engage when not needed. If you are using the AE-L/AF-L button for focus then you have managed to separate focus function from metering and VR function and thus you can use the auto-focus happily without using the power for the VR of the lens (and withoug having to turn it off on the lens side-button meanin that if you want to take the shot you can just do so, the lens and camera is ready).
Premetered Flash mode
This is even less obvious for most people. Have you ever used the Nikon i-TTL system to take flash shots of your pets? Then you know that the camera sends out a pre-flash to meter on just before the main flash is sent out. This makes cats and dogs and other animals with good reflexes to close their eyes and you end up with a picture that’s not so good.
If you scroll down the menu you will find an entry there that say FV-Lock. The way this works is ingenious. By pressing the AE-L/AF-L button you can control the pre-flash used to meter before the main flash is used. So this is what you will do:
- Frame and compose your shot carefully
- Focus automatically or manually as you prefer
- Press the AE-L/AF-L button, the flash will flash and the camera will meter and remember the flash value.
- Now, wait till the right moment and take the picture. The flash will go off without pre-flash and you will have a perfect picture of your pets!
This is also very useful when working with still pictures, it saves energy in the flash head and especially when working with a flash through an umbrella that means you may go much further on one set of batteries!
Remember that you need to do another pre-flash when you re-compose the picture, change angles or anything else that affects the light in the picture!