Controlling the Flash

Do you want to have full control of the flash? Here comes an explanation that will get you on the way to really be able to master the use of flash—at least flash mounted on the camera. There is of course a lot more to flash photography, but that will have to way to another time—and many more posts. This tip here will hopefully without too much work help you understand how you can control the flash in some ways.

Before we start, as you may know; in October last year I started what I called a new instalment for me. On and off I wanted to show and write about simple tips, tips that can improve anyone’s photography. I have written about using long shutter speed to make different photos, I have talked about moving close to the subject to create relationships and I have mentioned how you can using natural reflections—such as sunshine reflected from the streets in through doors—to create beautiful light in your photos.

Alas, I have also had a couple of posts about how to get most out of the camera-mounted flash or the built-in flash on compact cameras. It’s time to take the flash one step further. As written in previous posts you can adjust the amount of flash that is emitted by dialling up or down the flash compensation dial. At the same time you can also adjust the general exposure by the exposure compensation dial where you can make the picture darker or lighter by increments of ⅓ or ½ exposure values (E.V.). The latter will influence both the exposure of the available light as well as the exposure by the flash.

Now this means that you can actually adjust the ratio between the available light and the flash light and thus fine-tune your exposure. This may sound a little complicated, but hopefully it is not. Try to think—when using a combination of both available light and flash—that you are taken two images at once, one with available light and the other with the flash. These two images are then superimposed upon each other (of course this all happens as one exposure in the camera. What I am writing here is just to create a visual image in order to understand how the camera is dealing with the combination of available light and flash).

The flash light has a limited range and will only affect objects closer than one and half to three meters (or yards) away from the flash head depending on the maximum emitted light possible from the flash. The available light, on the other hand, will expose everything within the frame, up front and in the background. Now let’s go back to this idea of two different exposures superimposed upon each other. First the camera takes a photo with the available light and then one, in which it adds the flash (again this is not how it actually happens; it all happens in one take, naturally). Now if the exposure by the available light is correct and makes a perfectly exposed photo, then when you add a flash on top of this the objects that are close enough to be reached by the light from the flash will be overexpose. The rest, further away, will still be perfectly exposed (only by the available light). To compensate for this the camera needs to underexpose the available light on whatever is reached by the light from the flash. However, the camera cannot do this partially, thus everything will be underexposed in the first photo taken only by the available light. And then when you now add the flash, those objects in the reach of the flash will get added light and thus (if everything is correctly added) be properly exposed while the background will be somewhat underexposed—which is generally quit OK.

This is usually done automatically by the camera, and can be used in different ways as I wrote in the previous posts about flash photography.

Now I want to raise the stakes. So far I haven’t been dealing with situations where the available light is different in different parts of the scene. Particularly when the foreground is dark and the background is well illuminated, the use of flash can improve the photo significantly. In this case you can get around the problem by thinking that the background is going to be exposed only by the available light hitting it while the foreground is illuminated by only the flash.

You work it out this way: Figure out the correct exposure for the background. In many ways setting the camera to Manual exposure mode is the simplest in this case, but if don’t want to I suggest selecting Aperture Priority mode (if you have a compact camera set the mode to Slow Sync). You may have to underexpose the subject since the foreground is so dark and will influence the cameras evaluation for a suggested exposure. Maybe start with dialling in –1 E.V. At this point you have a background that is exposed as you want to.

Now it’s time to add the flash. Turn it on. Give it a try without any compensation. Since the foreground is dark, it might be just the perfect exposure. If you are not quite happy with the exposure from the flash, just dial up or down the flash compensation dial till you have what you want. One thing to keep in mind: Sometimes when you are in Aperture Priority mode and turn on the flash the camera will automatically underexpose the general exposure. In this case you will have to compensate for this, by making the available light brighter. For instance, you may have to go from –1 E.V to no compensation at all—or even more like +⅓ E.V. However, since this compensation also will affects the exposure of the light from the flash, you have to do an equal amount of compensation on the flash, but the opposite way. So in the example above, you will either need to set the flash to –1 E.V. or -1⅓ E.V.

The photo above is an example in which I used this technique. I used the available light to expose the background and the sky and then used a flash to light the guy in front. (By the way it’s a photo I have shown before on this blog).

If you have any questions to this technique, please don’t hesitate to ask in comments below. I will answer to the best of my abilities.

For the previous posts on flash photography, please look up: Flash Away the Shadows, A Flashy Look and Flash for the Night.

Facts about the photo: The photo was taken with a Canon T90 camera (with analogue film) and a 24 mm lens. It was captured at ½ a second and f/2.8 (set to expose the background as I wanted it). Flash was added and set to -⅓ E.V. No tripod. Finally the photo was scanned and processed in Lightroom and Photoshop.

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