Shooting flash in the broad daylight always seems to bother people for some reason. I think that people are afraid that it’s complicated or some black art that is impossible to master. Listen, flash is just a self contained light that is run by batteries. Nothing magically about it or really hard to understand. The light from a flash works exactly the same way sunlight works or any other light. It has color, it will drop off in intensity over distance (square inverse law) and you can shape it. Probably the biggest reason people are suspect of flash in the daytime is that most camera can not do it well so you get blown out images or the traditional “hot spot” in the face or it’s still dark even though the flash fired.
To really use flash in the daytime, get manual. Forget that you spent a large sum of money on a camera that can virtually think for it’s self, put the dial on M for manual and learn how to set things up the way YOU want it. When I learned to shoot film, there was a rule pounded in to our collective heads. It’s been somewhat forgotten now by the users of digital but it is called the “Sunny Rule of 16”. For a bright sunny day, set the camera to ISO (ASA) 100, shutter to 1/125 (1/100) and F16 on the lens. That will get you 95% there for a properly lit exposure in bright sunlight. Once you have that, you can adjust each parameter and work out the others pretty easily.
What we need to know is that when shooting flash on a sunny day (or any other time) is that your shutter speed controls the ambient light and that the aperture controls the flash exposure. Why? Because the flash duration can be something like 1/42,000 (1/128 power) of a second which is way faster than your camera’s shutter at it’s best. Even at full power, the typical small flash is about 1/2000 of a second flash duration. And when you are shoot at 1/250-1/320 sync speeds, the flash is still way faster than your shutter speed. Since aperture controls how MUCH light comes in, you can adjust the intensity of the flash by either opening or closing the blades. Wide open is more light in and stopped down means alot less light is coming in.
The shutter on the other hand controls how LONG the light will hit the sensor or film. Short shutter speed means less exposure and longer shutter means more exposure. So if the flash is 1/32,000 of second long, when your shutter is at 1/200 second, you will get how ever much flash light there will be in that 1/32,000 of a second. What you CAN adjust with the shutter is the AMBIENT light. Or in this case, how bright the daylight will be. Slow shutter means lots of exposure and a short shutter means less ambient light. In the two images below, I shot both with exactly the same shutter and ISO but I added a Neutral Density Filter X2 which works just like pushing the aperture to F22 ( 1 stop) which my 50mm can not do.
This shows how the aperture adjusts the ambient light while the shutter and ISO stayed the same. What does that mean for us with a flash? Well, all things being equal, you can dial in your exposure with the flash by tweaking on the F stop. Of course, you need to have some range to do this, about F5.6 to start would be nice and thats tough in broad daylight. But not impossible. Lets do some math 🙂
If I start at ISO 100 and 1/125 shutter with F16 and I want to go lower on my F stop, how can I do that? I can drop ISO which I can not right now and I can UP the shutter speed controls my ambient light. So I raise my shutter 1/250, thats one F stop and I can cheat a bit and go to 1/320 shutter, thats two full F stops. So now I’m at ISO 100, 1/320 shutter and F8. With a neutral desity filter X2, I can go down one more F stop to F 5.6 which is right where I want to be. My exposure has not changed from the first set at ISO 100, 1/125 and F16. So now I have less depth of field, I have about 3 stops to work the ambient light to darken skies etc.
So this means that I have the ability to dial down the sky and use my flash to light up my subject even though it’s high noon or if I want a bit more drama at sunset. OK.. ok.. so enough about this ambient light stuff, how do we use a flash? Pretty easy when you think about it. When you have the ISO at 100, the shutter at 1/125 and F16 for your aperture, the typical small flash like the SB800 needs to be eight feet away and full power to give the proper exposure.
You can see that we can easily light up the subject with an SB800 from about 8 feet away. But what if we wanted to use less than full power? Or get depth of field? Easily done by juggling the parameters. Lets bring the flash in to about 4 feet and cut the power to 1/2. Nothing else has changed. ISO, Shutter and F stop are still the same. I did zoom in a bit tighter so you can see the lighting closely.
Now what if I wanted to darken the background a bit more. Remember, ambient light is controlled by my shutter so I will raise my shutter one stop to 1/320 which is about the max I can go with my wireless triggers before I start cutting off the image with the shutter shadow.
You can see the exposure of the subject is the same but the background went a bit darker. So now what happens if I use one of those plastic diffusers? The kind that comes with the SB800 and snaps onto the front? Well, it means I can move my flash way in close and get softer light since the size of the light source relative to the subject has gotten alot bigger than when it was 8 feet away. I’m still at 1/2 power, broad daylight with the same shutter and ISO settings. Just closer and with the diffuser.
You can easily see that the diffuser eats a fair amount of light. But the tradeoff is that you can get much better quality of light when you are so close like this that it’s a pretty good trade off.
I hope you can see from the images that understanding daylight use of the flash is not that hard once you keep some basic rules in your head. It’s not very magically but it is very useful. These images are just simple demonstrations of the ideas but I will be putting up some real portrait work later using these same ideas. So get out there with your flash and light something up.
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