Using your flash as a main light

The main light in this photo, the flash, is only 2X stronger than the natural light.

The main light in this photo, the flash, is only 2X stronger than the natural light.

When you are using your flash as a main light, you have made some decisions. First off, the lighting conditions where you are taking your photo are less than ideal and you have to light with the flash, meaning you want the flash strength to overpower the existing natural light. This means that while you are preparing to take the photo, there is a good chance that the exposure meter inside your camera is going to read as a minor or massive underexposure. This is not a big deal as we are going to add flash and still get a proper exposure for our subject.

The flash has a built in function that measures the amount of light put out by the flash according to the ASA/ISO and aperture you have set. Once the proper amount of light is produced by the flash, it will shut off the light burst. Remember, the idea here, not ideal lighting, so, you decide that your flash will be the main source of light, your exposure meter should read in the negative, registering as an underexposure.

The first step is choosing a shutter speed that is going to work with the flash, you can choose up to your maximum flash synch speed some camera’s can go up to 1/500 sec, 1/250 sec and 1/200 sec are common in today’s digital SLRs. You can choose slower shutter speeds, but, remember, once you get below 1/60th sec., you run the risk of showing camera shake especially if you are shooting handheld. You can also run the risk of showing any subject movement, depending on the actual subject’s movements. Remember, the shutter speed and aperture combination you choose will always show as an underexposure in this case as we are lighting the subject with our flash, using it as the main source of light.

The next is choosing your ASA/ISO according to your preferences, inside you will find you are using 400 ASA/ISO for average photos, in studio would find you using 100 ASA/ISO or 200 ASA/ISO.

1/60th sec, f/36, light source flash, set 5 X more than the natural light.

1/60th sec, f/36, light source flash, set 5 X more than the natural light.

Now comes the hard part, determining the aperture to set which ultimately controls the power of the light being output by the flash. A couple things to consider when doing this are: how strong do you want your flash as a main light and the distance your subject is from you. Let’s take a simple example to start with. In a normal classroom environment, I have a natural light exposure: shutter speed 1/30 sec., aperture f/5.6 and ASA/ISO 400 sensitivity. Subject is about 5 feet/1.5 metres away. First problem, I can’t go to a wider aperture to use 1/60 sec. for shutter speed which would help insure that I don’t have any camera shake or movement and I don’t want to increase my sensitivity setting as it will get too noisy. In order for me to make my shutter speed faster, I will need to add more light to have a proper exposure. So, I am going to use the flash to add the necessary light. On this example all I am going to do is to turn the flash on, change my shutter speed to 1/60 sec and turn the flash on. From there I take a photo. There will be several things to notice in the photo, first, the background hasn’t gone too dark. Why, because the difference in the main light (flash) and fill light (the room light) is only 1 stop. Why, because we changed the shutter speed only one stop from our initial readings. Because an item in digital photography can handle up to 2 stops of underexposure and still register in the frame, we still see detail in the lit areas around the subject. Let’s take the same example above, duplicating everything except changing the aperture to f/16, making sure that the subject is in proper range to take a photo at this aperture (double check the distance scale on the back of the flash). Take the photo. Notice how the lighting in the background has been rendered much darker? That is because now, while the main light flash exposure is correct, the fill light has become 3 stops underexposed. Considering the fact that maximum underexposure latitude in digital is 2 stops, what is underexposed fades quickly to black.

Most amateur problems with using the flash are that they are trying to use too much flash to light a subject up. They will set apertures of around f/16, requiring a lot of light to be output by their flash and they are too far away. It’s actually better to use a wider aperture of f/5.6 and be a little closer to the subject, lighting them well and not totally overriding the natural light in the setting.

CNW News



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