Sunday, March 22, 2009

Combining flash with ambient exposure

I've always heard that the best way to learn something is to teach it. I've been concentrating on techniques related to balancing flash and ambient exposure lately. My recent (March 5) post, "Control flash for snappier images" made its way into a newsletter article for my photo society this month. I have two classes coming up in May, where I'll include this idea. Needless to say, I've been thinking about this concept more than usual.

My friends in the Grand Lake Camera Club in Grove, Oklahoma, asked me to come speak at their meeting last week. I talked about it there, as well. But, based on some of the feedback I received, I think I still have more to learn. To be honest, as with many things I do in photography, I've taken concepts I've heard or read about and sort of "intuited" how to accomplish them. Trying to teach others, however, forces me to think through them more carefully than is my habit.

One of my friends from the Grand Lake club asked some clarifying questions by email. For instance, what flash sync speed she should use? Based on what I thought I had presented, this shouldn't have been a consideration. So, I must have missed the mark, at least a little.

In my talk, I think I described both "fill flash" and "dragging the shutter." It appears that I placed all the techniques for balancing flash with ambient light under the umbrella term, dragging the shutter. In considering my reply to her, I think I arrived at a more useful summary of the lighting approaches you can employ, using only your camera and either on-camera or external flash for more interesting photographs.

In planning your exposure—you do plan, don't you?—you have all the exposure tools your camera offers to capture the existing light. You also have a pop-up flash on most cameras, or you can attach an external flash.

For any shot, unless you're using automatic settings, you will decide on your primary source of light and set exposure for that light source. In a studio, this would be termed your key light. To simplify the discussion, flash can be thought of as either on- or off-camera. So, you will plan an exposure using ambient light or flash. In some cases, either will do. However, if you're near the extremes of bright or dark, you won't have a choice in the type of light is primary in the exposure. But you can choose to add the other type of light, and this will usually produce a more complex and, I would argue, pleasing image.

So, your options for exposing an image with typical equipment are the following:

  1. Normal to bright ambient light:

    • Ambient light only, with no flash

    • Ambient light with some flash mixed in ("fill flash")

  2. Normal to dim light (or darkness)

    • Flash-only image

    • Flash with some ambient background exposure ("dragging the shutter")

The amount of light available will determine which strategies you can use. By combining ambient with flash light, you are reducing the amount of contrast between the brightest and darkest areas of your image.

In normal to bright light, add in fill flash by forcing your flash to fire. If the ambient light is too bright for flash to have any additional impact, adjust to the lowest ISO, and you might even need to add neutral density filter(s) to lower your how much ambient light your camera sees. The flash added back in can then be balanced with the ambient light.

In normal to dim light, add in ambiently-lit background by adjusting the ISO upward till you can get the amount of exposure you want, using normal or near-normal camera exposure settings (shutter/aperture). The flash portion of the exposure will be determined by through-the-lens (TTL) flash metering. Adjust the amount of flash using flash exposure compensation, and adjust the background with aperture and shutter.

Even though the techniques seem very similar, bright or dim light will determine your starting point, when you select the primary source of light appropriate for the scene. The easy way to think of it is this:
  • In bright light, use camera exposure and add fill flash to fill in shadows.

  • In dim light, use flash exposure and drag the shutter (boost ambient exposure) to add some background.

These concepts may seem complicated at first. Once you start to employ them and see their effect in your images, you'll find that they're not so complicated, after all. They often increase the quality of the images where you use them.

Thursday, March 5, 2009

Control flash for snappier images

Many people think the hallmark of “amateur” photography is on-camera flash, with blown out faces, dark backgrounds and red eye. In low light, most modern cameras will pop that little sucker up and give you that “special” quality your mother (or grandmother!) achieved with her Instamatic camera equipped with its flash bar or flash cube. It’s not uncommon for an aspiring photographer to set his camera so that the flash will not fire at all, in an attempt to achieve more “professional” results. What they often achieve is rather dull and flat. Just because it’s a dinky little pop-up feature doesn’t mean your camera’s flash can’t help you achieve some amazing results and add sparkle to those dull images.

On page 106, my camera’s owner’s manual describes “Flash Exposure Compensation.” If you learn this technique, I guarantee you will improve the quality of your candid photography. Here’s why. Any scene has a certain amount of light available in a range of what’s called exposure values (EV). This is a way of describing the range from the brightest to the dimmest illumination in the scene you’re photographing. In the picture below, on the left, part of my model’s face and the top of her hand has bright light from direct overhead sun. Her hand shades her face – especially her eyes. The difference between these two levels of light is somewhere between four and five stops of light.

Your camera can correctly expose for either extreme, whether very bright or very dim. But when you try to capture both in one image, you’ll either blow out your highlights trying to capture the shadows, or you’ll lose detail in the shadows trying to capture the bright areas.

On my camera, a Canon 30D, if I press the flash button near the pop-up flash, my flash will fire, no matter how much light there is in the scene. In other words, even in bright sunlight, when the automatic settings would not ordinarily cause the flash to fire, I can make it fire. This is called fill flash. But how much is too much, and how much is too little? Because this is a manual flash mode, there is no flash metering. The image exposure is actually metered off the ambient light, as if there were no flash. And the flash has a set amount of power, so it could be way too bright or not bright enough.

My owner’s manual shows me the button on the top of my camera that lets me control the level of light the flash applies. By default, it’s set in the middle of a range of plus or minus two stops. Using my Quick Control Dial (a wheel on the back of my camera), I can adjust the level of the flash in 1/3 steps through this two stop range. The dial will show me how much or how little I’ve changed the flash power. It will only take a couple of test shots at the most to adjust the amount of flash to balance out the lighting of the scene; that is, to fill in the shadows.
Unless you shoot with a Canon 30D, your camera’s controls will operate differently. But most modern DSLR cameras, for sure, and some point and shoot models, will provide this capability. Read the section of your owner’s manual that covers your built-in flash. It may be called, simply, fill flash. But the manual should tell you how to control the amount of light your flash puts out

Using flash compensation, the picture on the right shows my model’s face in the same setting with the same amount of sunlight and the same basic exposure—f/14 at 1/100 sec and ISO 100—but the fill flash provided light in the shadows and also put a “catch light” in her eyes. I encourage you to experiment with this technique. When you’re in a brightly lit place, like outdoors in bright sun, or if you’re indoors in a relatively dim room, you can set your camera’s regular exposure for the ambient light and then provide a balanced amount of light from your built-in (or external) flash that will make your images snap. Professional photographers have a number of tools in their toolbags. This is one of the most versatile. Using it will help you achieve professional-quality results.