How to Use Flash Value Lock (FV Lock) on the Nikon D7200
FV Lock (Flash Value Lock) enables you to lock flash power at any time before you fully depress the shutter button. By default, the Nikon D7200 camera measures the light throughout the entire frame to calculate exposure and flash settings when you press the shutter button halfway.
But it adjusts those settings up to the time you press the shutter button fully to record the image, ensuring that exposure remains correct even if the light changes between your initial shutter button press and the image capture.
Here’s the most common reason for using this feature: Suppose that you want to compose your photo so that your subject is located at the edge of the frame. You frame the scene initially so the subject is at the center of the frame, lock the flash power, and then reframe. If you don’t lock the flash value, the camera calculates flash power on your final framing, which could be inappropriate for your subject. You also can use FV Lock to maintain a consistent flash power for a series of shots.
This feature is one of the few advanced flash options that works in Auto mode and in the Scene and Effects modes that permit flash — but only if the camera sees the need for flash in the first place. In Food Scene mode, you must pop up the flash to use flash. However, FV Lock is available only for viewfinder photography; it doesn’t work in Live View mode. And when using the built-in flash, you must use the TTL setting for the Flash Cntrl for Built-in Flash option on the Custom Setting menu. (That setting is the default.)
Regardless of your exposure mode, you can’t use FV Lock until you first assign the function to the Fn button, which is set up by default to give you access to the Image Area setting (DX or 1.3x crop), or to the Depth of Field Preview button (which normally lets you see how your f-stop will affect depth of field). You can also give the FV Lock button to the AE-L/AF-L button, but that’s not recommended because the button’s normal role (to lock exposure and focus) is one you may use often.
The fastest way to change a button function is to display the i button menu. Choose Assign Fn button or Assign Preview button and select FV Lock as the setting.
After assigning a button to the FV Lock feature, follow these steps to use it:
Frame the shot so that your subject is in the center of the viewfinder.
Press and hold the shutter button halfway to engage the exposure meter and, if autofocusing is used, set focus.
Press and release the button that you assigned to FV Lock.
The flash fires a brief light to determine the correct flash power. When flash power is locked, you see a little flash symbol with the letter L at the left end of the viewfinder. The same symbol appears in the Information display (look in the upper-left corner of the screen).
Recompose the picture if desired and then take the shot.
To disable FV Lock, press the assigned button again.