Flash can be a confusing addition for many new photographers. But there’s really only one way to gain experience. Learning to use your flash well takes practice.
Using your flash without modifying its output often produces unsatisfactory results. These can be very discouraging. With little modification, you can achieve more acceptable results pretty easily. Controlling the output of your flash based on the style of light you want for your photos is not hard to do.
Your unmodified flash is a small light source
The smaller your light source is in relation to your subject, the harder the light will be. An unmodified flash produces strong light and high contrast for most subjects. This creates a hard-edged shadow which is often undesirable. The only difference is with macro photography because the light source will be larger than the subject.
Modifying the output of your flash by using a diffuser softens the light which falls on your subject.
Using a diffuser does a couple of things. It subdues the output, so less light hits your subject. It also spreads the light, effectively making the active light source larger. The light falling on your subject will be softer. So will the shadows they create.
The benefits of using modified flash
Diffusing the light from your flash will produce more flattering results when taking portraits. Soft light falling on the skin reduces the appearance of texture and gives it a more even tone. There are a number of techniques and accessories you can employ to diffuse the light from your flash. I will discuss some of these in the next section.
Hard light from an unmodified flash is more likely to show up skin blemishes. It also produces unsightly hot spots.
These bright patches occur with all but the most light absorbent surfaces when using an undiffused light. The more reflective the surface, the more light from a small light source will reflect.
Using some method of scattering the light from your flash will help end these problems.
Another option to modify your flash is to do the opposite of spreading the light. Narrowing the dispersion of the light produces a completely different look. You can better control what area of your composition the light from your flash will affect. This is usually achieved by the use of a snoot or honeycomb grid.
How to control your flash using modifiers
The most simple way to alter the light from your flash is to turn your flash head so it’s not pointing where your lens is focused. Indoors you can point it up to the ceiling. The light will reflect off the ceiling and scatter. You can alternatively point your flash towards a wall beside or behind you.
Ceilings are often white or light neutral colors, so your photo is not likely to be affected by an odd toning. Bouncing your flash off a colored wall or other surfaces can cause that color to affect the light.
Depending on how close your flash is to the surface you’re bouncing it off will determine how much it is diffused. The closer you are to the surface, the less diffusion there will be.
When you turn your flash head to bounce it off another surface, the light and shadows it creates will be softer. Shadows may still be evident. You need to be careful of shadows under people’s chins and around their eyes when you bounce your flash off a ceiling.
Using a piece of whiteboard, plastic or a fold-out reflector to bounce your flash off will give you more control. You can move your reflector further away or closer and determine the best position for it.
Clip-on hard diffuser
Most flash units come with a clip-on hard plastic diffuser. This is a small attachment that fits over the front of the flash head. It scatters and softens the light when the flash is fired.
Because this attachment is small, about the same size as your flash lens, it will not do a lot to soften the light. It is often better than nothing if you have not other option and it is small and convenient.
Bounce cards and other compact modifiers
A white piece of cardboard about 20cm (8 in) square with a tab on one edge and a couple of good strong elastic bands. This was a standard kit for photographers when I worked in newspapers. It was back before the proliferation of flash modifiers were available to buy.
Adding a bounce card to a flash pointed at a ceiling or wall spreads and softens the light even more. This will help further reduce the strength of the shadows.
Snoots and grids
Most accessories which modify flash output are designed to soften the light. Snoots and honeycomb grids are two pieces of kit which can help you control the direction of the light.
Each works to narrow the spread of light from your flash. This allows you to control which part of your composition is most affected.
Gobos and colored gels
A gobo is a stencil or template placed in front of your flash head to create a shadow of a shape or pattern.
Any color gel can be used to affect the color of light which emits from your flash. This can be used for creative effect or to balance your flash with the ambient light.
Electric light sources often emit a colored light that is not as white as the light from your flash. Tungsten light is a warm tone. Fluorescent is often quite cool. Using the correct color gel can produce the right color to balance with an existing light source.
Small flash softbox
My favorite flash modifier is a small softbox. It’s not the smallest or most convenient, but it produces a soft, pleasant light.
Mine’s about 60cm (2 ft) square and has a bracket to mount the flash at the back. The biggest drawback in using it is that you need to place it on a stand or have someone hold it for you.
I find I like the results best when using it as a fill light.
Controlling the amount of light
Whichever method you use to you modify the light from your flash there will always be a reduced output. You must compensate for this.
Using the TTL setting your camera and flash should calculate the correct amount of light. This should also be true with the auto settings.
In some circumstances, you may notice not enough light from your flash is illuminating your subject. At these times, you must adjust your compensation. This can be done by opening your aperture more or increasing your ISO.
Unmodified flash is not often the best light source. Modification allows you to control its output to suit the style of photograph you are making.
Experimentation and practice are required to master the type of lighting you want.
A practical exercise to help you understand and see what you can achieve is worth spending some time with. Set up a still life composition or find a willing model to work with. In the same setting, take a series of photos using various modifiers so you can compare the way the light looks with each one.