Manual Exposure With External Flash

Did you know that when you set your Nikon camera to manual exposure mode that your flash is still on automatic exposure? Why should you care?

This happy combination of manual camera exposure and auto flash exposure is a big deal to me. Your main subject can be well-exposed by the flash, while the ambient light in the background can be controlled by how you set the manual exposure.

Nothing screams amateur like indoor flash shots with jet-black backgrounds. If, instead, you expose the background about 1 to 2 stops under (using the camera meter), then your main subject can be exposed properly by the flash while the background (which is out of range of the flash) is pleasingly de-emphasized.

If you use “FP” mode on your external flash, then you can even use this technique outdoors at whatever shutter speed and aperture combination that suits the scene. The flash “FP” mode allows any shutter speed, while filling in those nasty shadows in someone’s face under their eyes and nose. Your subject, of course, needs to be within range of the flash. The camera internal flash cannot be set to FP mode. Canon calls it HSS (High Speed Sync). Lower-end cameras may not offer this feature.

If you set “Auto FP” mode for your external flash, then it’s a set-and-forget scenario. Your flash will go into FP mode when you set a high shutter speed, or else stay in the usual high-power-short-flash-duration mode with lower shutter speeds. My cameras are always configured this way.

FP mode uses a series of quick flash bursts while your shutter is open, so it’s like continuous light. The quick bursts overlap each other just enough to seem like the flash is on the whole time the shutter is open. Any motion-stopping capability only resides in the shutter speed you use and not the flash. Be aware that the overall light intensity is reduced, so your flash won’t have the usual range. Expect to lose about 2 stops of flash intensity. Here’s a good resource on flash here.

In case you’re wondering, “FP” is short for “focal plane”, and it really has nothing to do with an electronic flash. It alludes to special old-time “FP” flash bulbs that had long-burning characteristics, so that they would burn the whole time your “focal plane” shutter was open. This mode emulates that same long-burning flash bulb.

You might need a neutral density filter if you’re using a really wide aperture in the sun, but the flash fill light really makes your subject pop (it adds that sparkle to the eyes).

Please use bounce flash or a flash diffuser indoors when you can, or you risk getting those nasty hard shadows you really don’t want to see. Even the old lens tissue over flash with rubber band can be really helpful if you can’t use bounce. Diffusing the light will rob even more flash power, however. I guess that’s why they sell those powerful pro flashes.

Macro photography outdoors using flash FP mode and manual exposure is a marriage made in heaven. It’s the cat’s pajamas. It’s the bee’s knees. You get the picture. Yet another pun, sorry.

To summarize, when you set your camera to “manual”, you use it set the background (ambient) exposure to your taste. The flash will (usually) handle the foreground subject exposure.

Check out a real pro like Neil van Niekerk here to appreciate what flash photography can do for you. I’m not worthy.

Samples of Using Manual Exposure and Flash FP Mode