Flash photography; the basics

A Tiger Longwing Butterfly lit by using flash.

A Tiger Longwing Butterfly lit by using flash.

What is a flash? Basically, it’s a light that you turn on when it is dark. A camera flash can really only be used in two photographic applications. It is either a main light or a fill light. What does that mean? Well, basically, if you are going to use your flash as a main light, it is the strongest source of light in your photo. If you are going to use it as a fill light, then it is the weaker light source in the photo, perhaps your stronger light source may be the sunlight, other light source or even another flash unit.

A late 1800's printing press.

A late 1800’s printing press.

The Mechanics

The camera flash is a portable light source powered by batteries, therefore, there is not a constant power supply. You turn on the flash and the batteries activate, they charge a capacitor and it is from this capacitor that the flash tube draws its power and fires. The capacitor is constantly being recharged by the batteries throughout the operation of the flash. When batteries are low, it takes a longer time to charge the capacitor, also, if a lot of power is being used from the capacitor to fire the flash, it will need time to recharge, meaning you can’t always rapidly fire the flash. It depends on how much power you are drawing.

Types of Flashes

Today there are really only two types of flashes to worry about, TTL dedicated and non dedicated. The TTL dedicated flashes are very easy to use, you turn them on and the camera on and all adjustments done in camera will affect the TTL dedicated flash. The TTL stands for “Through The Lens” and all metering and exposure information is measured through the lens. Non dedicated flashes do exist still, the easiest example is studio flashes, where you need a hand held meter to measure the light. This article won’t be dealing with studio strobes, but, some of the principle rules of using flash with your camera apply. There are other non dedicated flashes out there, usually off brand flashes but, they are slowly disappearing.

Getting Started

When you use your flash there are a few simple things you have to be aware of. First, what shutter speed do you set? Each camera has what is known as the maximum flash synch speed, the fastest shutter speed that can be set for your camera to work properly with flash. On older cameras, this was quite slow. Today’s modern cameras can allow up to 1/500 second and even faster with some special programs. Your camera’s maximum flash synch speed will be enclosed in the specs from the manufacturer, however, in today’s camera’s it is quite simple to find. Just turn your TTL dedicated flash on (pop up flash or the add on flash purchased to work TTL dedicated with the camera you have), start increasing your shutter speed and it won’t allow you to go past the maximum flash synch speed with the flash on. Normal maximum flash synch speeds can range depending on the camera, so, if you are not sure, do the test above. What is common today for a maximum flash synch speed on most camera models is either 1/180 sec., 1/200 sec., or 1/250 sec.

Camera and flash The flash display tells you the information you need for proper exposure.

Camera and flash
The flash display tells you the information
you need for proper exposure.

Now that we have established what shutter speed to use, what controls the output of the light from the flash? The aperture you set. As you change apertures on your camera and take pictures with flash, you will note that the power output of the flash is more or less, depending on the aperture you set. Once you set that aperture, you will have certain distances that the flash will work in.

The built in pop up flashes are very weak flashes, not very powerful, so, their range is very limited, maybe up to 10 feet at wide apertures and 3 feet at small apertures. Mid range flashes increase the working distance, however, they don’t always have visual clues to let you know you have made the right decision. Top of the line flashes will actually tell you on the back what your range of coverage is with the aperture you have set. For example, at ISO 400 I have an aperture set of f/8. My flash (Nikon SB800) will tell me that I can cover subjects from 1.1 meter (approximately three feet) away to 13 meters (thirty nine feet) away and have a proper exposure.

There is another method for calculating flash power, using the guide number (at ISO 100) supplied by the manufacturer, you would find the working distance in a mathematical formula:

  • Flash Range = Guide Number / Aperture.

However, today’s modern camera flashes are made to have the user not have to worry about math and they do a pretty good job of that.

Choosing the ISO to use

When you are choosing the proper ISO to use with the flash, several things will bear into mind. First off, because you are adding light, you can use a lower ISO. High speed ISO like 800 or 1600 are really only to be used in low natural light situations where you can’t use flash. You will find that you will set normal ISO settings when you are using flash, 100/200 is possible, 400 is more normal.

Mode Settings

Most flashes have a few mode settings. First there is TTL automatic which stands for Through The Lens. The measurement of the light output is done at the CCD, through the lens. Second is A- Automatic. The measurement of light output is done by a sensor on the front of the flash. Next is M- Manual. The flash output is not measured by the camera at all, you adjust the power output of the flash manually, calculating distance and the proper aperture.

There are also repeating flash modes where the flash will fire several times during exposure and different curtain synch modes. These initial articles deal with using the flash in TTL automatic mode, the mode set by default on a flash when it comes from the factory and the mode used by default by most pop up flashes. If you are unsure of how to set the mode, you must consult your manuals for the flash mode of TTL Automatic.

Putting it Together

So, we now know a bunch of things we need to know to start using the flash. We have set our mode at TTL Automatic, we have set a shutter speed no faster than our maximum synch speed, we have set our ISO to the proper setting and we are using the aperture to control the output of the flash. The rest of the decisions will be based on whether you are using the flash as a main light or a fill light.



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