1. Question: What are the advantages of using fill in flash?
2. Fill in flash provides a more natural effect to flash
3. pictures and if used properly, will provide an image more
akin to what the eye actually sees.
4. It can be used to add "sparkle" to a subjects' eyes.
5. It can "lift" a subject and make the colours seem more vivid.
6. You can provide your own "sunlight" anywhere, anytime. Your subject doesn't have to face the sun and squint.
7. If you print your own pictures you will find that you have less "messing" about in the darkroom in terms of trying to burn in the background after taking a picture and exposing for a shadowy subject, thus leaving the back ground to overexpose. This is because fill in flash reduces excessive contrast and softens shadows in harsh light.
8. If shooting an interior, which includes a window, you can prevent that window from "burning" out and make the lighting appear more natural. With correct use of this technique the actual brightness of the window can be varied.

If we remember that fill in flash is used to balance the foreground lighting with that of the background, then you will realise that this technique can be used at any time of the day or night.

A lot of the misunderstandings about flash photography come about from a basic lack of knowledge about the relationship between the flash exposure and the exposure for the existing light. You must remember that EVERY flash photograph consists of both a flash exposure and an ambient light exposure. Whenever you take a flash picture you are recording not only the flash first but also any available light that was present at the time.

With conventional flash photography the flash properly exposes the subject and the ambient or background light is often underexposed. This is because the guide number formula determines the aperture, and the shutter speed is usually at or near the camera's maximum synch speed. As a result the flash level is often higher than that of the existing light.

In order to balance the background with the subject in flash pictures, it is necessary to control the ambient exposure level recorded on film. When ambient exposure for the BACKGROUND is dominant, the flash exposure level is called a fill or fill-in. In other words, if the flash exposure is controlled to be less than or equal to the ambient exposure level, then the flash exposure will only effect or fill-in the shaded or backlit areas of the subject.

There are two types of fill-in flash photography. In bright light, like sunshine, the existing light is dominant and the flash exposure must balance to this. In low light situations where the flash exposure is usually dominant the existing light exposure must increase to match or nearly match that of the flash.

THE KEY ISSUE THEREFORE IN ALL TYPES OF FLASH PHOTOGRAPHY IS HOW TO CONTROL THE COMBINATION OF FLASH EXPOSURE AND AMBIENT EXPOSURE.

TECHNIQUE

Before we get into the technicalities of proper fill-in flash photography we must understand two things:

A) Ambient exposure control is completely separate from flash exposure control.

There are different methods of getting a proper fill-in flash effect depending upon what type of equipment you own.

First, take a normal meter reading to determine the correct exposure for your subject as if you were going to take the picture WITHOUT flash. Remember to take the reading with the camera set to its flash synch speed eg. 1/60th sec or whatever depends on the make. Let's say that the reading you get is 1/60th @ f8. You must then set your flashgun at f8 for 1:1 lighting effect or at f5.6 for a 1:2 lighting effect. A 1:1 lighting ratio has the effect of matching the daylight and normally looks unreal because it completely kills the shadows. A better effect is gained by using a 1:2 or a 1:4, which would mean using f4 in our example. Remember that we are trying to slightly fill-in the shadows.

S.L.R. CAMERA PLUS FLASHGUN WITH ONLY TWO APERTURES.

If you are using a flash unit that only has a limited number of apertures to choose from, for example, f4 and f8 then there is no reason not to make use of the fill-in technique. The only slight drawback is that you will probably be restricted to a 1:2 or 1:4 ratio but as these are pretty much the proper ratios to work with then maybe it isn't much of a drawback after all.

On a separate note. If you are using an independent brand of flashgun, which is dedicated to your particular camera, you can obtain the fill in effect in the following way. First take your reading of the overall scene and determine the correct exposure. If the reading is something like 1/60th at f8 and you are using 100 ISO film then to get a 1:2 lighting ratio simply set the flash units film speed dial to 200 ISO. For a 1:4 ratio set the film speed dial to 400 ISO. This has the effect of "fooling" the unit into giving out a half or a quarter less light and saves you from having to keep on adjusting the lens aperture.

I've saved the most complicated 'till last. If your flashgun is of the manual type then every time you take a flash picture the flashgun completely discharges itself, giving out the same amount of flash each time. One of the ways of achieving the fill-in flash effect is to vary the FLASH TO SUBJECT DISTANCE. Of course if you want to be mobile, then you are going to have to attach the flash to the camera and make sure that your distance from the subject doesn't change. You can get closer to or further from the subject with the aid of interchangeable lenses. You can also vary the flash unit's output by attaching a neutral density filter to it. These N.D. filters are available in a variety of strengths and can be used singly or in combination to achieve the effect you want. If your expenses don't run to a set of N.D. filters, then you can place a polarising filter over the flash tube. This has the effect of cutting the light output by a stop and a third.

If you want to find out the correct aperture to use for a manual flashgun then you must divide the flash unit guide number by the flash to subject distance. For example, if the guide number for the flash is 28 (in feet) and the subject is five feet away, then you must divide 28 by 5 which will give you 5.6 which is the correct aperture to use.