The Flash Power Challenge

So from my posts, you have seen that in using flash outdoors, the big challenge is:

To make the background darker without also affecting the flash power to the point that it is no longer sufficient.

To make an outdoors background darker, other than actually making it darker (sometimes the simplest option is the obvious one: wait for a solar eclipse, shoot later in the day, or use scrims), you can do four things:

  1. Use ND filters
  2. Decrease aperture (use a higher “F-number”)
  3. Decrease ISO
  4. Increase the shutter speed

Unfortunately, the first three of those also affect the flash: every use of those will negatively affect your flashes’ available range too. So you want to avoid them if possible.

And what about the shutter speed?

That does not affect your flash range. So it is the obvious one to use to make the background darker. But… only up to your camera’s synch speed (depending on your camera, this is normally around 1/250th sec). Beyond that, you cannot use flash.

“Yes you can, Michael, you can use Hi-Speed (Auto FP) flash”, I hear you say.  That is true – but that too negatively affects your flash range. Catch-22! So no, it does not help with your flash power. (Then why do we have it? Ah.. to allow outdoors shots with the blurry backgrounds that only large apertures will give you.. apertures that need fast shutter speeds!)

So. Again, as said yesterday, a nicely balanced outdoors flash picture (i.e one in which the background is darker), needs you to first of all use method 4 above, up to your flash sync speed.

After that, you must do one or more of of the folowing to still have enough flash power:

  1. Bring the flash closer.
  2. Forego the use of modifiers and use direct flash.
  3. Add more flashes.
  4. Use more powerful flashes (strobes instead of speedlights).
  5. Zoom in your flashes to concentrate the light (giving you more intensity over a smaller area).

Work though the logic of this post very carefully. Step by step – the logic is important, and it is important that you thoroughly understand it. This is not esoteric theory: this directs you in every day shooting, every single day!

Flash balancing, step by step

Many of you have asked me to give a simple step-by-step instruction of how to balance light using flash. OK, so here we go.

Step one: the normal shot.

Say you are shooting outdoors. And the background is bright. So you get this shot:

Flash demo photo by Michael Willems

1. Background too bright

OK for the foreground – but the background is too bright.

Step two: expose the background right

So you need to darken it. If, say, you are in Aperture mode, just use exposure compensation of, say, -1 to -2 stops. Now you get this:

Flash demo photo by Michael Willems

2. background ok, foreground too bright

Great, the lake is visible.

But now the foreground is too dark. So you need to brighten it.

Step three: expose the foreground with flash.

OK: turn on your flash. That gives you this:

Flash demo photo by Michael Willems

3. Better, now with flash

Much better. If the foreground is too bright, use flash exposure compensation (not exposure compensation!) to darken the flash. Or if it is too dark, you are probably too far away – get closer or use higher ISO, if able.

If your shutter speed exceeds your flash sync speed (around 1/200th second), reduce it or use Auto FP Flash/High Speed Flash (in that case, get really close).

Now you can make shots like this:

A Park Bench in Oakville (Photo by Michael Willems)

A Park Bench in Oakville shot with flash

(Can you also see the half CTO warming gel I used?)

And you can get more dramatic: here, I underexposed the background by two or more stops:

A Stop Sign in Oakville (Photo by Michael Willems)

A Stop Sign in Oakville (Photo by Michael Willems)

Have fun!

Fast Flash!

To exceed your camera’s maximum flash sync speed (which is something around 1/200th – 1/250th second), you need high speed flash (Auto FP flash, in Nikon terminology) where the flash pulses at ca. 40kHz instead of firing all at once.

You need an external flash for this, like an SB900 or a 580 EX.

  • When you need it: when you need to exceed your flash sync speed, e.g. when taking an outdoors picture of close object with blurry background. That means low F-number, which means even at 100 ISO you’ll need fast shutter speeds.
  • Advantage: in theory, you can you can go to any fast shutter speed and still use flash.
  • Drawback: you lose much power, so that Fast Flash is usually only suitable for close-by subjects.

The Shot: Shoot a close object or person with blurry background. To achieve this, set your camera to A/Av mode, and select a wide open aperture (f/2.8,say). (If your lens cannot go down to f/2.8 or it is a very dull day, you may need to go to 400 ISO).

You should now be exceeding your flash synch speed-if you set your flash to Fast Flash. Else you get an overexposed picture (your camera will refuse to go faster).

Note, your object has to be close, especially if you get to speeds of 1/1000th o rfaster. Else, your flash will not have enough power.

And now you can get this – the following image was lit by flash at 1/1600th second, at f.2.8!