Nikon’s latest DSLR cameras come with the feature to lock exposure settings and other parameters like Autofocus, Focus point area, flash value etc. When the exposure is set for the shot, or when the camera acquires auto focus on the subject, or when we want to lock the flash value, we can use the lock feature to lock those settings so that it won’t change inadvertently during the shooting. We discussed about Auto Exposure Lock (AE-L) previously, and today, we are going to discuss about the Flash Value lock (FV Lock) feature.
The basic idea is common between these two features. Auto Exposure Lock feature is use to lock the exposure value and the Flash Value Lock is use to lock the flash power. This feature comes very handy when we are shooting in camera’s default metering mode, matrix metering mode, in which the camera calculates the exposure and the flash setting by taking the information from the entire frame rather than the subject itself. Let’s say we put the subject in the middle of the frame, lock the focus on the subject and press the shutter release button halfway down to calculate the exposure. Now, if we continue pressing the shutter release button all the way down and take a picture, there would be no issue and the camera would balance the overall exposure of the subject and the background image. But, let’s say, we don’t want to put the subject in the middle of the frame and want to recompose the shot. As soon as we move the camera to recompose, metering system will calculate the new exposure value and the flash setting based on the new information from the frame. If the new composition has more darker area, camera will increase the flash power to compensate for the less available light and it would result into the overexposed subject when we press the shutter release button to take the picture. Now, let’s see how can we solve the problem by locking the flash value.
How can we lock the Flash Value?
To solve this problem, we can program the camera’s function button or even AE-L/AF-L button to activate the Flash Value Lock (FV Lock) feature once the button is pressed. When we program either of these two buttons for the FV Lock, next thing we would have to do is point the camera/flash towards the subject, press the shutter release button half way down which locks the focus on the subject and meters the exposure. We would then lock the flash value by pressing the FV Lock button, which we just programmed. After pressing the FV lock button, camera will fire pre-flashes on the subject briefly and lock the flash power to properly expose the subject in given lighting situation. We would then recompose the shot by moving the subject inside the frame. After the flash value is locked, even if the lighting condition is changed in the frame by recomposing the shot, flash value will not be recalculated by the camera and stays in the previously locked value. When we are ready to take the shot, we will press the shutter release button and the flash will be fired with the power camera previously locked into. This will give the proper exposure to the subject ignoring the ambient light in the background.
Once we lock the flash value, it remains on that power setting unless we press the FV Lock button again, or the camera is turned off, or the light meter in the camera times out. We can increase the light meter timeout period but we have to be careful doing so, because it might drain the camera battery faster if we forget to bring it back to it’s default value after we are done shooting with the locked flash value.
In this photograph above, there is a mix of color tones and the lights in the background and the foreground. There is a dark table in the background and a white tablecloth in the foreground. She is wearing a dark color dress and he is wearing a white t-shirt. The lighting situation is bit tricky and I wanted to properly expose for the subjects and place them on the side of the frame rather than in the center of the frame (Rule of Thirds). This kind of a situation can confuse the camera light meter and flash may fire with the improper power setting. That is why I locked the flash value on the subject, recomposed the frame and then took the shot.
Normally we should use the FV lock feature to meter the subject that is off-centered and the background is bit darker.