This pill is a trick to use the TTL automation of our camera to measure the correct exposure for a scene for both continuous lights both flash lights that add to the scene. Many cameras have Flash exposure lock function (On Nikon FV Lock - Flash Value Lock). Personally, I use a trick that works in this way:
- Set the exposure meter to central spot for the measurement of continues light
- Target with the spot where the continuous light is greater
- Lock the exposure by pressing the AE-L * (the camera sets the correct torque speed / aperture for the continues lighting)
- Now I move the spot to a point where the flash will arrive stronger
- Use the FV Lock button to send a bit of flash so that my camera measures the intensity of the flash right on that point.
In this way the camera will analyze all the data and will ensure that the sum of the continuous light (measured in EV then time – aperture) with that of the flash so that the scene is not overexposed. Obviously it is an empirical measurement method and you have a lot of experience to understand the behavior of the camera and how the camera interprets the measurement. By the time you will know compensate the exposure of both the continuous light, both that of the flash light with the buttons of compensation light.
*Usually the button AE-L / AF-L serves as both a block of exposure from that block of focus, personally imposed this button from the menu of my camera in such a way that acts only by AE-L for exposure lock while to the focus using the shutter button half