Learn how the Shutter Speed affects your flash photos – flash photography tips

Flash photography tips - has this ever happened to you? You take a portrait using your built-in or external flash, but the photo is too bright or too dark, like the slightly over-exposed couple and wedding register on the table in the above shot.

What did you do to fix it?:-

  • Use exposure compensation
  • Change from aperture to shutter priority or vice versa
  • Change the flash exposure compensation (FEC)
  • Change the ISO

Well, there is no one quick answer, it all depends on what part of the image was over or under-exposed and your creative intention when taking the photo. But it helps to know that when using flash, changing the shutter speed has absolutely no effect on the light from the flash. That's because the flash burst of light is almost instantaneous, much faster than any of your typical shutter speeds when using flash. Changing the shutter speed only affects the ambient light.

Here's a quick lighting setup outside my house during a sunny day. I put a speedlight on a stand and took a series of shots of the wall (extremely interesting subject!!). I used the camera's Manual mode and I only adjusted the shutter speed between shots.

You can see that the light on the wall from the flash is exactly the same in every shot, but the ambient light is getting lighter as I slow the shutter speed.

FlashOnWall01

FlashOnWall02

FlashOnWall03

FlashOnWall04

FlashOnWall05

FlashOnWall06

FlashOnWall07
 

...until eventually, the light from the flash on the wall is perfectly balanced with the ambient light.

So how does this help?

In the wedding photo at the top of the page, I used Manual mode and made a guess of the exposure, it was only a test shot, but the couple are over-exposed. The settings were f4, 1/160th, ISO 800. (higher ISO to bring in some ambient light as I didn't want the background to go too dark).
This was a simple one to fix, I just wanted the whole image a little darker, including the backgound, I also knew that it was the ambient light that was causing the over-exposure and not the flash (as it was in i-TTL mode), so I changed the shutter speed to 1/250th.

weddinggoodexp

Here's the same settings used, but with the flash turned off, you can see that the background is only a little darker than in the shot above where the flash did fire, that's because I set my exposure to bring in the background area. It's only lit by the ambient light, the couple are unlit now, so they're too dark.

weddingnoflashexp

2017-05-29T16:22:15+00:00

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