Flash photography has been used for decades, and the technology has evolved quite a bit. Nonetheless, there are some basic techniques and principles that should be understood and utilized whenever considering and/or using flash in your photography.
Do you actually need to be using a flash?
This is, obviously, a subjective matter, but the things to keep in mind when deciding that are going to decide that for you.
- How much ambient light do you have available to you and where is it falling in your frame
- What sort of light ratio is the ambient providing
- What sort of light ratio are you trying to achieve
Ultimately if you’re using flash it’s because there isn’t enough light somewhere. It could be broad daylight in the early afternoon, but if the sun is creating overly harsh shadows that you don’t want, you might need something to fill them in some.
Well, first off you want to get a decent flash. The unit that comes attached to your camera, no matter how expensive the model, is probably going to provide tragically unpleasant results (again, this is all subjective, but 8.9 out of 10 of you will probably agree). Depending on your budget, take a look at the various makes and models available. Something will be suitable, preferably a model that allows you to move and rotate the flash head in various directions.
So here you are, flash in hand, and skeptical because you know what a crap flash photo looks like, and you’re not sure how to avoid it. And you just need the extra light.
Well, for one, try not to look at flash lighting in such a negative way. It can serve a very utilitarian function, sure, but it can also be its own aesthetic, for better or worse. Yes, flash can be used heavy-handedly, but subtlety needn’t be lost just because you’re wielding a hammer. You just need to know how to get what you want and also get an idea of the versatility a decent flash can offer you.
Shutter Speed, Aperture, ISO and Flash
One important aspect of a flash unit is the speed with which it illuminates. You can adjust the amount of light a flash exposes your film plain/image sensor plain to. Flash units typically do this by adjusting the length of time the flash bulb is lit. One might assume all three exposure controls (shutter speed, aperture and ISO) will affect how much light hits your plain regardless of whether it’s ambient or coming from a flash. And one would be right in all regards, save shutter speed. The brevity of the flash of light from a flash is measured in thousandths to tens of thousandths of a second. In all likelihood your shutter speed will be slower even than 1/1000th of a second, which means no matter what your shutter speed, it won’t affect the brightness of a surface illuminated by your flash. It will, however, affect the brightness or exposure of anything lit by the ambient light, which means anything not being hit by that flash is going to get brighter or darker depending on which way you go with those settings. And that directly affects the lighting ratio of your shot. Your ISO and aperture settings, on the other hand, will brighten or darken your whole frame.
The Nature of Flash (and Lighting in General)
Another thing that affects the amount of light that will hit you plain is proximity. The distance between your subject and the light source (your flash) dictates, in part, how much of that light is going to be reflected by your subject back to the camera. A flash has a cone shaped beam. That means that the closer it is to the subject the narrower that light will be, possibly casting a vignette of sorts around whatever is lit by the flash, assuming there is nothing directly behind it, or close by. The light, in this instance, would be more intense. Conversely, if you were to move away from the subject, forcing the light from a flash to travel a greater distance, it would broaden the area where the light falls, and diminish the intensity of the light. As the light cone widens, less of it is actually hitting any given surface. The light could be at such a distance, thus so thinned, that it becomes ineffectually faint. But why? Well, as with all the fun parts of photography, there’s math involved. The relationship between luminance and distance between light source and subject is a square one. Twice the distance means a quarter the light. But that is true of the distance between the light source and the subject it is illuminating, not the distance between the camera and the lit subject. That being said, if you have a camera-mounted flash, then the distance between the light source and the subject is the same as the distance between the camera and the source. So, if you want to shoot at some distance from your subject, with flash, you’ll need an off-camera flash. The main point to keep in mind is that relationship between light source and subject. And the manner in which that distance is quantified is called the “Guide Number”.
The strength of a flash unit, at a specific ISO, is measured as the maximum distance from the flash to the subject (usually in feet) multiplied by the number of the f-stop, which will provide a proper exposure. The standard ISO used to determine this is 100. The Guide number changes based on what the aperture and/or ISO is set to.
One big point most people will make early on is that you should avoid pointing your flash directly at your subject, especially if you’re indoors, in an effort to avoid those harsh, flat shadows everyone seems to find so unappealing. Try bouncing the light off the wall and/or ceiling to diffuse it. A softer light can do wonders for interior shots, again unless you’re really into hard shadows. If you go off the wall it can also provide a less obtrusive angle for the light. Otherwise, try a flash diffuser attachment. That can be especially helpful in an exterior location where there aren’t so many walls and ceilings available.
Another thing you really need to consider when shooting with flash is your white balance. The color temperature of a flash is not to same as daylight or tungsten balanced lights. Tungsten light runs at about 2500-3500 Kelvin, electronic flash is about 5000-6500 K and daylight can range from 5000-6500 K. If you white balance to your flash, you can expect an orange tinge to whatever is lit by the ambient, tungsten light, or a bluish hue to whatever is lit by the ambient daylight. You can compensate for this by filtering your flash to match the white balance for whatever your ambient light is. Then again, you might like the effect of differing color temperatures. Experiment.
If you’re feeling particularly experimental, you can try to achieve flash blur, or slow sync flash. This is done by setting your shutter speed to something slow, like 1/30th of a second, panning your camera quickly, which would typically blur the image and using your flash at a speed that will freeze the action of your subject. It effectively gives you a motion-blurred background and a sharp subject, assuming the light from the flash doesn’t fall on the background too.
Speaking of backgrounds, if you’re trying to create a natural feeling image, try to put some space between your subject and whatever large object is behind them or it. Otherwise you run the risk of having hard, unsightly shadows cast on the background, which can feel distinctly artificial and staged. If you want the quality of your light to maintain a semblance of authenticity, think of your flash as something of a fill light, brightening up shadows and things too dark to be as visible as you’d like.
As much as flash units have progressed over the years, they still serve a very basic function: providing extra light. Past that, as complicated looking as a flash can get these days, they’re pretty simple devices. Sometimes you’ll need one, sometimes you won’t. But it’s obviously better to know how to manage one when the time comes. ;od luck, shoot well.