Three Things Every Photographer Needs to Know About Electronic Flash

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Someone recently asked for a “super basic lesson on flash” in, as they said, “one or two steps.”  When I say flash, I mean supplementary light that is being used when documenting people, places or things as they are presented to you. I am NOT talking about studio work, where you can control the light and the subject. I am talking about when the photographer has to react to the subject and the light as they are given.


The first “rule” is that all good flash is flash fill. What I mean by that is that the key to good flash is to position yourself, the photographer, so that the subject you are photographing is in the (relative) dark and yet has some light on the background behind it, no matter how little.  (The subject also needs to be a few feet away from any wall or other lit background because that is typically where the flash will cast it’s ugly shadow.)  Then you set your exposure for that background. After this, you have the flash fill in enough light in the dark area to make the once dark foreground now approximately match the lighted background. This is called balancing the flash exposure with the ambient light.

Keep in mind that as long as the foreground subject itself is darker by the exposure value of two or more f/stops, as compared to that background and if you expose for that background, that area behind the subject will look good and the subject will be black (if you were not using the flash.)  The difference between subject and background can be more than two stops, but not less.  If there is no difference, there is no point in using flash. If there is only one stop difference you risk ghosting, where the subject is blurry because the available light filled it in and they (or you moved) so everything is a blurry mess.

The way the camera experiences the scene is, the shutter opens and the background is correctly exposed, even if the background gets blurred by camera shake. In the foreground, that dark area is not exposed and stays black, until the flash goes off and fills it in. The flash goes off at a speed of between about 1/500 and 1/1500 of a second, so the subject that is illuminated with the flash will be frozen and sharp (assuming you focused correctly on that.) You may end up with what seems like an abnormally slow shutter speed to get a good exposure for the background, such as 1/2 or 1/4 of a second, which means that the background may have movement and blur. Since the foreground is getting light from the very short duration of the flash and is very sharp, it does not matter if the background is blurry. In fact, such a blurry background often makes the photos look better, giving the image a feeling of energy or atmosphere.

Positioning yourself so the subject is in less light than the background (by two or more stops) is the key. If the background is pitch black, frankly, there is nothing you can do. If the subject is right up against a wall then the flash will cast a nasty shadow on that wall and again, there is nothing you can do. 

The easiest way to think about this is look at your darker subject as if you wanted to make it a silhouette. Move yourself around so there is light behind it.  You can even photograph it as silhouette if you want to both make that picture and appreciate the strategy I am talking about.  In fact, if you look at a lot of my work, the best silhouettes could easily be made as interesting by filling in the dark area with a flash.  So, rule number one is “all good flash is flash fill,” as in putting light from the flash into an area that is two or more stops darker than the background, which is what you set your exposure for.

The second rule is that light comes out of the flash (or almost any light source) in a straight line and the way that this light falls on the subject forms a plane that is the second key to good flash photography. To understand this, think about how we all have pictures from an event with people sitting at a table, lined up such that they receding away from the photographer.  In the typical picture, the closest person is over-exposed by the flash, the person at the middle distance is correctly exposed and the far person is underexposed.  In this case, the “plane” that the flash is throwing at the subject lights things the wrong way when it hits the subjects straight on. 

The plane that matters is an imaginary line you can draw to the left (or right) of the people at that table that runs parallel to how they are sitting, closest to furthest. If you are facing them, as they recede away from the camera and you put your left hand (free of a camera) straight out, the line of your arm should parallel the plane I am describing. 

Understanding that plane is very important, because no matter how people sit or stand you can usually (not always) find a plane where all of the subjects are equal distance from the flash. If they are all equal distance from the flash (though not necessarily equal distance from the camera) they will all get the same amount of light on them from the flash. Keep in mind that the plane I am describing is almost never the plane where the on-camera flash puts out its light. Bouncing the flash off a ceiling or wall is one way of changing that plane, ideally making the plane of the light match the plane of the subjects being photographed (and illuminated by the flash.)

The best way to resolve the problem of matching the plane of the light of the flash to the plane of the subject is to get the flash off of the camera, which is the third key to good electronic flash photography. An external hand-held flash is simply required if you are going to use electronic flash effectively and creatively.

If you think about most of your best photos with natural or found light (as compared to controlled light,) they are rarely ones where the light was coming from the same direction as the camera was looking at the scene.  Side lighting, rim lighting, backlighting all make for much more interesting photos than frontal lighting. The same is true with your electronic flash.

A hand held, off camera flash lets you control where the light of the flash falls. This is important in terms of getting the light parallel to the plane that I previously described. Even if the plane is not an issue, being able to direct the flash at the subject from a different side and/or high or low gives you great creative control.

To fully appreciate how these three rules play out in my photography, look at some of my previous podcasts and blog entries on the subject, including Flash Photography Using Remote (Off Camera) Flash Units and The latest in electronic flash in my camera bag and Using flash and slow shutter speed when photographing

A few things to keep in mind: 

Learning to position yourself so that the main subject is in light that is two or more stops darker than the background will take time. A great exercise is to continually be looking around you in every day situations to find scenes with the lighted background, dark foreground lighting that I have described. If you can photograph those situations, first as a silhouette and then with flash, you will rapidly ratchet up your flash skills.

Learning to see that plane I have described also takes practice. Again, looking at everyday situations to find that plane and then doing some test photographs, no matter how seemingly ordinary, will help you refine your ability to visualize that plane. Digital cameras, with their instant results make this process a lot easier than it was in the “bad old” days of film.

Learning to hold your electronic flash off the camera in just the right position to parallel the plane as I have described will require further practice. Again, the instant review available with digital cameras will speed up the learning process. But it still requires a slow, methodical process to learn. 

There are, in the cases of all three of these rules, no easy short cuts.

The final thing to keep in mind is that the best electronic flash work requires a TTL flash, where the flash and camera “talk” to each other to read the amount of light hitting the camera’s light sensing chip in order to get the best exposure. Those calculations are done “through the lens,” which is why the flashes are called TTL units, and have the most accurate flash controls. This compares with the older “automatic” units where sensors on the flash itself did most of the calculation.

In the older flash units, the communication between the camera and the flash was done through remote (or off-camera) flash cables that clipped onto the bottom of the flash’s hot shoe at one end of that cable. The other end of that same cable was locked into the hot shoe atop the camera.  This system worked reasonably well, though managing the cables was a bit of a hassle. The newer cameras use various radio frequency technologies to send that same information wirelessly, which is clearly a great improvement.

The other technological improvement with the better electronic flash units is the ability to vary the output of the flash itself. The idea is that once you get a good exposure for the background, you then set your flash to fill in the darkened foreground. When you look at the image on your camera’s display you may decide you want the light on the subject to be more or less intense in order to drive the viewer’s attention to the subject. You may want the subject to have a harsh “deer in headlights” look or you may want something with less light and more of a mood.  Varying the output from the flash unit, which is usually but not always a control right on the flash, gives you this ability.

For much of my time doing flash photography, the rule was that only the camera manufacturer’s flashes were made well enough (electronically) to communicate with the ever more sophisticated cameras. From what I have read, that seems to be changing with aftermarket flashes improving each year and offering substantially better value for dollar. Having said that, I am sticking with my Olympus made flash units that communicate perfectly with my Olympus cameras.

Will there be situations where this system will not work? Sure! The most common is when you are photographing a situation where there is NOTHING with light on it in the background. However, if you get in the habit of looking around, to find some kind of light in the background, you usually will find some light to use as the background. These situations are less common then you might think. You usually can find some background. Also, moving the flash off the camera and paying attention to the plane in this type of situation will still result in better flash work.

Most people who take my classes in flash photography tell me roughly the same thing at the end. They say "These rules revolutionized their flash photography." Later they often tell me how much practice they have to go through to actually get to the point where they could implement these same guides. The best part is how people tell me that they "now enjoy using flash rather than dreading it like they used to." That makes the super basic lesson on flash very worthwhile for them (and for me.)