2. D850 Online Manual
3. Using Shoe-Mounted Flash Units
4. FV Lock

This feature is used to lock flash output, allowing photographs to be recomposed without changing the flash level and ensuring that flash output is appropriate to the subject even when the subject is not positioned in the center of the frame. Flash output is adjusted automatically for any changes in ISO sensitivity and aperture. FV lock is available with CLS compatible flash units only (0 The Nikon Creative Lighting System (CLS)).

To use FV lock:

1. Assign FV lock to a camera control.

   Assign FV lock to a control using Custom Setting f1 (Custom control assignment, 0 Custom Control Assignment).

   

2. Attach a CLS-compatible flash unit.

   Mount a CLS-compatible flash unit (0 CLS-Compatible Flash Units) on the camera accessory shoe.

3. Set the flash unit to the appropriate mode.

   Turn the flash unit on and set the flash mode to TTL, monitor pre-flash qA, or monitor pre-flash A. See the documentation provided with the flash unit for details.

4. Focus.

   Position the subject in the center of the frame and press the shutter-release button halfway to focus.

   

   

5. Lock flash level.

   After confirming that the flash-ready indicator (M) is displayed in the viewfinder, press the control selected in Step 1. The flash will emit a monitor preflash to determine the appropriate flash level. Flash output will be locked at this level and FV lock icon (e) will appear in the viewfinder.

   

6. Recompose the photograph.

   

7. Take the photograph.

   Press the shutter-release button the rest of the way down to shoot. If desired, additional pictures can be taken without releasing FV lock.

8. Release FV lock.

   Press the control selected in Step 1 to release FV lock. Confirm that the FV lock icon (e) is no longer displayed in the viewfinder.