Using your flash as a fill light

Balancing flash with the outside lighting was necessary for this sawmill photo.

Balancing flash with the outside lighting was necessary for this sawmill photo.

Basically, all a fill light does is fill in the shadows of a subject, usually created by a directional main light. The easiest example to quote is that a person is standing outside with sunlight falling on one side of their face. The camera left side of their face is towards the light, the camera right side farthest away. Our camera angle is right in front of them, seeing their full face. The camera left side will be lit by the sunlight , the camera right side will fall into shadow. It’s this shadow we want to fill in.

The camera left side is sunlight, the right side is fill flash.

The camera left side is sunlight, the right side is fill flash.

The way to do this is to establish your base exposure. That is the natural reflected light highlight exposure. Go in close to the side of the face that is lit, fill the frame with the cheek, and come up with the proper exposure. What you must keep in mind in setting the base exposure is that you are going to use a fill flash on the subject, so, you must set a base exposure based on the maximum shutter speed you can set and use flash. So, if your fastest flash synch speed is 1/200th sec. set the base exposure of using no faster than 1/200th sec. shutter speed. From there, the output of the flash will be governed by whatever aperture you set, so, if your aperture is set to f/8 for the base exposure, when you stand back and recompose the photo and turn the flash on, it will output the flash power to give you a proper f/8 exposure on the subject. This is how you do basic fill flash on a side lit subject.

Where this gets a little difficult is that under the conditions above, we will have an evenly lit photo, the fill light the same power as the main light. We can adjust this by doing all of the above, but, we may want to adjust the flash exposure compensation (check your manual to find this setting) to reduce the amount of fill light being output by the flash. In photography, we want a little bit of shadow in a side lit photo to show some modelling and dimension in the photo. If we get rid of all the shadow we produce a flat, two dimensional photo. If we adjust the fill light, the shadow will be filled in, just not to the same strength as the main light. What is common to use for flash exposure compensation on a fill light is no more than -2 stops. Anything past that is beyond the range of exposure latitude and the same as not using a flash at all.

A back lit butterfly filled in with fill flash.

A back lit butterfly filled in with fill flash.

Our next common example of when to use the fill flash is when you have a subject against a lit background, the sky for example. Depending on how you set your exposure, you will get either a silhouette photo or a photo exposed for the subject and blowing out the background. So, what we are going to do is decide to do a base exposure based on the light outside, balancing for it. Fill the frame in your camera with an area that is brightest outside. Come up with the proper exposure based on that. Keep in mind, you are going to use a flash, so, the shutter speed can be no more than your maximum flash synch speed. Let’s say, my base exposure for the outside light is 1/125th sec. at f/11, my ISO is 100. Now, as I put my subject in front of this window, if I just take the photo, they will be in silhouette. So, I just want to turn my flash on to fill them in. No harder than that. The amount of light being put out is controlled by the aperture set and this will give a roughly evenly lit photo between back light and front light. So, take a measurement behind the subject, then when you are ready you just turn the flash on. Again, you can vary this with your flash exposure compensation (look in your camera or flash manual for this) depending on the effect you want.

When using flash, remember, you have to make a conscious decision, am I going to use it as a main light or a fill light? You have to be aware of the apertures you set and the working distances you have at those apertures. If you are too far away for the aperture you have set, the flash output won’t reach the subject. Also, you need to be aware that there are also some distances that will be too close with your flash, depending on your situation. Generally, using a pop up flash and average add on flash, your minimum distance will be about 1 metre/3 feet. Finally, remember your flash synch speed, the maximum shutter speed you can set and use your flash. You can set slower speeds and still use it, but, not faster.

Well, hopefully this helps with your photography, gives you some basic flash technique to work with. Practice the backlighting and side lighting situations. See what happens when you try flash exposure compensation and always try to shoot comparison photos, one with flash, one without to show you accurately what is being accomplished.

CNW News

 


 

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