Day 53: Flash Has Two Different Exposures

Welcome to day 53 in my 100 days of photography series! Today we are at day three of a ten day lighting series, and I wanted to talk about flash exposure. If you’ve missed the last two days, be sure to catch up because so far we have talked about the inverse square law and the relationship between the subject and size of the light.

Today we are talking about another lighting principle that will help you determine why your image is or isn’t working and how you can create the images you want using flash.

I will start by saying, when your flash is your main light source, your shutter speed controls the ambient light.

When you take a photo with flash, you’re working with two different exposures, which is perhaps the reason that flash is so intimidating. Your first exposure is determined by your camera settings just as it always is. If you turn off your flash and take a photo, that is your ambient exposure. It might look a little dark and yellow, but it’s there! The second exposure is determined by your flash and your flash will freeze your subject.

This might be a bit confusing, so this might help: Have you ever gone to a science museum and there is a display where a string is moving next to a strobe? You turn the flashing strobe light off and you can see the string is moving very quickly… so quickly your eye has trouble even seeing it really. Then you turn on the flashing strobe and you can see the string start to freeze? If you have no idea what I’m talking about, you can see it here:


The light is freezing the string just like your flash will freeze your subject.

Knowing that, what is your ambient exposure doing? It’s controlling everything the flash isn’t hitting. Knowing also that the shutter controls the ambient exposure, slowing your shutter down will do a few things. First, it will allow more background details to be let in. I slow my shutter to 1/50th of a second or less when shooting receptions. Lowering it even more might create a ghosting effect.

In the image below, you can see the two different exposures. My shutter was crazy slow, maybe 1/15th of a second. The couple is frozen in flash but because the shutter was so slow, you can see the ghosting around the edges of his shirt. You can also see it really well on the guy on the right. You can see the flash exposure of his arm having a crisp outline but then you can see a haze around him which is the ambient exposure. Because he was moving and because my shutter was slow, we can really see the two separate exposures in play.

Some photographers really love ghosting in their reception images. It can create a hazy effect that makes you feel like you’re inside of the image. I believe, that like anything else, ghosting has a time and place and while I don’t use this effect in every image, it can be fun to play with!

In this next image (taken seconds later), the shutter is increased to 1/80th of a second, making the ambient exposure mesh with the flash exposure to the point that you can’t separate the two.

You can also see how the ambient exposure is in play below. At the top image, my flash was my main light source. It hit the table and that’s about it. You can see the ceremony site behind but it’s dark. So I absolutely plunged my shutter down to maybe a half of a second and look what happened. The flash isn’t reaching the mountains or the chairs back there, that’s all controlled by my shutter, which controls the ambient exposure.

Next time you’re at a reception, try to slow your shutter to 1/15th of a second and photograph people dancing. See if you can pick up the ghosting effect. As you speed up or slow down your shutter, check out what happens to your background. If you ever find yourself with a couple dancing and they’re perfectly lit but your background is one big dark mass, slow your shutter to help out with your ambient exposure.

Whew. Are you with me? I know these can be overwhelming at first but seriously, read this series until it clicks! I can’t tell you how many times I watched the same video or read the same article until it finally clicked in my brain! Knowing these lighting principles will allow you to create images you want with flash!

Tomorrow is day 54: Why is there a big black bar on my photos?

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