Read an Excerpt
The Expanded Guide
By Robert Harrington
AE Publications LtdCopyright © 2013 AE Publication Ltd
All rights reserved.
The basics of flash
One of the most overused yet misunderstood pieces of photographic equipment is the flash. Here's a guide to the fundamentals.
Flash (noun): a brief, sudden burst of light The biggest advantage of the flash that's either built into your camera or an external unit such as a Nikon SB910 or a Canon 600 X-RT is the ability to add light to your images, but the biggest disadvantage is the complex nature of flash that puts many off to using it to its full potential. Understanding the nomenclature, the buttons, and dials on the flash itself, and the menus inside, is akin to trying to learn a foreign language in only a week: it's impossible.
What in the world is FEC? What does TTL mean and how do we use it effectively? What is high-speed synchronization? How are we as photographers, most of us non-engineering-types, going to understand the complexities of these systems and put them to effective use in the field? Picking up a manual full of technical jargon is a daunting task, considering what is inside is just as confusing as the flash itself. When you purchase your flash, you usually follow something called the "Guide Number. But what is a guide number? Is it related to subject distance responding to flash output, shutter speed, aperture, and ISO, or is it just a number that gives us a total flash power rating? That's the problem. As modern-day photographers used to picking up a camera and having it do all the work for us, some of the foundations that are used to build a good technical understanding of photography have gone to the wayside. How are we to understand what a "Guide Number" is if we've never had to deal with the concept?
The automation of photography is one of the greatest gifts in photography. Now, anyone can pick up any kind of camera and capture a great image. Along with computer software, even the worst image we've ever taken can be turned into art, worthy of a gallery or the wall of your home. But we really need the lessons of the past to understand the current trends in flash photography, so we can fully begin to understand the flash on or off our cameras.
Let's jump right in here and look at the basics of flash. Let's try to understand the concepts and numbers that cloud our thoughts, and see how we can get great images without spending an excessive amount of time in software: you may find that you're trying to fix images you could have captured properly in the first place.
First, let's look at "guide numbers." In the old days, in those photos where you see a press photographer holding an ancient Graflex camera with a bulb flash on the side, the photographer had to figure out subject-to-camera distance in order to set a shutter speed and aperture to capture an image his editor would accept for the next edition of the paper. So think about what is going through the photographer's head. In the amount of time it took to read this passage, the photographer figured it all out, set his camera and took a shot, replaced his flash bulb and film, and got ready for another shot: Whew!
As modern-day photographers, we need not concern ourselves with figuring all of that out — or do we? Understanding how guide numbers work will give us a greater understanding of how our flashes work and in what situations. To find the right guide number for your flash situation, you need only to look at simple math:
Guide Number = Distance x Aperture
Initial guide number calculations are based on an ISO of 100. As in all things in photography, if you change the aperture, distance, or ISO up or down the guide number will change reciprocally. But you need to find this initial starting point to figure that out. So if your subject distance is, say, 10ft (3m) and your aperture is f/5.6, then the guide number on your flash should be 56ft (17m) with your flash on full power, using all the power accessible to you. If you stop your aperture down, say, to f/8, then your distance halves to 28ft (8.5m). This is, of course, if you are working with the flash at full power. If you halve the power, then the distance, just like stopping the aperture down, halves to about 14ft (4.25m). These calculations are all based on using your flash with a bare head. The numbers will be affected by a great many variables, including putting a diffuser over the flash head, using an umbrella, or a softbox.
This does get easier. On the back of some flashes, there should be a Guide Number or GN setting. This takes the guesswork out of guide numbers, if you want to use them. On the back of a Nikon SB910, for instance, the GN setting gives you all the information you need. Set to an ISO of 200, it's base ISO setting, and the GN setting gives you the perfect flash output and subject distance. If I set my camera to Program Automatic, letting the camera choose everything, with a 50mm lens I get an ISO of 200, shutter speed of 1/60 sec., and an aperture of f/5. At these settings the flash will automatically tell me that my optimal camera-to-subject distance is 6.6ft (2m) with automatically adjusted flash output of between 5.8ft (1.77m) to 7.4ft (2.25m). In this mode, the camera will do everything for me.
If I swap settings and go to Manual Mode on my camera using the same 50mm lens and choose ISO 200, shutter speed 1/125 sec., and an aperture of f/8, the GN setting on the flash will automatically tell me the camera-to-subject distance of 6.6ft (2m), but the automatically adjusted output for the higher aperture will decrease a little and have an adjusted GN distance of 5ft (1.5m) to just under 7ft (2.1m). By choosing a faster shutter speed and smaller aperture, the overall distance is reduced a bit.
Guide numbers now have been relegated to the category of overall flash output. If you do a search for a new flash for your kit, you'll be thinking about guide numbers a lot. The guide number of a Nissin Di866 is 198ft (60m) at ISO 100, compared to the Nikon SB910, which is 111,5ft (34m) at ISO 100, or the Canon 600 EX-RT, which is 197ft (60m) at ISO 100. The units differ in overall flash output on the highest end of the guide number spectrum, so depending on your camera system or flash, you can shop using guide numbers as your gauge to the most powerful flash at optimal outputs for your needs.
Through the lens
Now that we've covered the basic and classical way of determining your flash-to-subject distance to obtain your optimal flash output for a correct exposure under perfect conditions, let's take a look at what your flash is capable of without any consideration for the math involved in determining your exposure. Everything that determines exposure on your camera — point and shoot or DSLR — is determined Through The Lens or TTL. The acronym TTL confuses a great deal of novice photographers. Through The Lens or TTL only means that the camera has the ability to automatically determine exposure by simply seeing the scene in front of it. All this information enters the camera through the lens.
When you point your camera toward something — landscape, seascape, a person, or whatever — the camera can only see the world through the lens. Get used to seeing, saying, and understanding this concept, because once you understand it, your photographic life becomes much easier. When you point your camera toward a subject, whatever that subject may be, you immediately get an exposure reading. Whether or not it is the correct exposure for the scene, or the correct exposure for the creative look you're after, is not the point: the point is that the camera sees the world and then determines all the variables needed for a correct exposure based on that scene.
For flash photography, TTL is based on the same concept. The camera sees the world, sets an exposure for a correct image capture, then tells the flash how much power output it needs to get light to your subject for a correct exposure using the flash. The TTL function automatically performs the Guide Number calculation for you, so while it's important for us as photographers to understand how Guide Numbers work, it becomes less important for us to understand how to employ them in our photography.
TTL is especially suited for on-camera flash. Although there is the use of TTL for off-camera flash while using certain radio triggers or in-camera exposure gauges such as Nikon's Creative Lighting System, we'll begin with on-camera flash.
On-camera TTL is a great way to begin to understand your flash. The camera and flash combination will choose everything for you until you decide that the result is less than desirable; then you take the next step into what is termed Flash Exposure Compensation, or FEC. Whether using your built-in popup flash, the flash on your point-and-shoot camera, or a speedlight, you have the ability to control flash output and override the chosen camera settings. FEC is simply controlling the output of your flash through the flash.
The LCD on the back of your camera becomes the most useful tool in determining your image and in creating the look that you desire. Having the ability to see an image right before you instead of having to wait for film development is a huge asset to the digital photographer. You can adjust exposure and light output right from your camera after you determine that your initial test shot needs more or less light or needs to be shot from a different angle, or just needs something more creative.
In the series of images below and overleaf all captured with on-camera popup flash, you can see the difference FEC makes in the image. This is also called "fill flash and is what you want to achieve when using direct on-camera flash: you don't want to overpower your subjects, just add a touch of light to lift the shadows and add a fill light, as if using a reflector. TTL-based flash is going to want to add enough light to illuminate your subject(s) completely, so the flash becomes the main light source. However, this may not be what you want in the final image. In this case you have the ability to adjust flash output by entering the flash's menu and adding or subtracting flash power manually.
Now that we've seen the effect you can get with a popup flash, let's take a look at the more powerful speedlight. The speedlight allows you multiple choices for how you want to attain your final image. With the speedlight set to TTL, your camera set to Program Auto to keep things simple, and with the head pointed directly toward your subject, you get a clean and well-exposed image according to what the camera sees. As the camera will always give you a correct exposure for the scene, it's important to note that what the camera gives you isn't always the best result.
But by simply using one control, Flash Exposure Compensation, you can adjust flash output for a desired result. FEC sounds like a complicated acronym holding inside of it a large and difficult series of changes to your flash, but in reality all it means is that you change the output of your flash to determine how much light you want on your subject. FEC is truly a simple concept that gets overlooked by many photographers, especially beginners, due to the fact that most of us are not engineers and camera and flash manuals are not written with us in mind. They are also written as though you have a full understanding of your flash and they simply spell out the instructions on where the buttons are and how to push them.
In the photo, far left, direct flash was employed. As you can see the camera wanted to give me a correct exposure all around. Not wanting to overpower my subject with a huge blast of flash, the remedy was to simply drop my FEC or just, in layman's terms, drop the power down on my flash so the subject was not overblown or washed out with light. By adjusting my flash power down -/ of a stop, I was able to add fill light to my subject without destroying her skin. At this point, I've used FEC simply and effectively to get a better end result in my photo.
Inverse square law and exposure
Let's move to one of the staples of basic lighting technique: the inverse square law. This principle will be applied later as we move into off-camera flash and light placement. But for now we'll touch on the subject here so you begin to understand light and its relative distance-to-subject ratios in order to get great results with your flash.
The inverse square law states that "..the intensity of the light source is inversely proportional to the square of the distance from the source of light." Basically what this means is that the further your subject is from your flash, the lower the amount of flash is going to reach them. So if you are at full power using direct flash and your subject is approximately 3ft (1m) from you, you'd need an aperture of f/16; if your subject moved back to 6ft (2m) away from you, you'd need an aperture of f/8; and if your subject moved 9ft (3m) away from you, you'd need an aperture of f/4 in order to capture enough light from your flash to illuminate your subject.
As your subject moves farther and farther away from you, the amount of flash power reaching it is diminished. The most noticeable place you'll find the inverse square law in action is in low light, when you are unable to get enough flash power to your subject and the background goes dark. As your subject moves away from you, the flash just doesn't have enough power to fully light the entire scene.
Modern digital cameras can combat the problem caused by the inverse square law in a number of ways:
1) Increasing the camera's ISO will Increase the sensor's sensitivity to ambient light and increase the amount of background (ambient) light affecting the exposure.
2) Exposure can be controlled manually. Instead of relying on the camera, take a test shot in Program Auto and check the results on the LCD screen. Then, switch to Manual Mode where you can adjust shutter speed and/or aperture to let more light in, thereby increasing the exposure and allowing the flash to work less hard.
For example, if the camera suggests an exposure of 1/60 sec. at f/5.6 (ISO 400) when it's set to Program Auto, switch to Manual Mode and set the shutter speed to 1/30 sec. and the aperture to f/4. This will increase the exposure by two full stops, making it easier for your flash to light your subject.
The inverse square law comes into play more when we begin to explore off-camera flash and lighting placement, especially with main light placement. This is an important concept to grasp. As we move farther along, well be seeing the effect of the inverse square law. Lighting placement is a direct result of our understanding of how light hits our subjects from the front, rear, and sides when using on- or off-camera flash. But the inverse square law also helps us to understand exposure and how to adjust our exposure. If we photograph our subject at 6ft (2m) away at 1/60 sec. at f/8 and then move back another 3ft (1 m) to 9ft (3m) then we know we can immediately adjust for at least a one stop difference in exposure from f/8 to f/5.6 to start. The one stop difference may not be enough — we may need to adjust to f/4 — but the idea is to begin understanding how lighting on our subject is affected by distance.
The inverse square law is directly linked to exposure. If we need to place our light somewhere, we need to understand how that light interacts with our subjects for shadow and fall off and all things related to light placement. We also need to understand how to expose properly for the light hitting the subject. The best way to learn this is to use your camera as a guide:
1) Set a scene in which to shoot a still life.
2) Use a tripod so you can move around the scene to see what is happening.
3) Set your camera to Program Auto and see what the camera chooses for shutter and aperture and jot that down on a piece of paper.
4) Then go to Manual Mode and set shutter and aperture manually. Once you've done this, you can completely control the camera.
5) Take a shot, view the LCD and Histogram, and go from there.
6) Next, put a flash on your camera and do the same thing over and over till you begin to understand how it works. Once you've got it, you've got it!
7) Finally, play with the inverse square law and keep your settings the same but move your subject farther away and see how it darkens as not enough light is hitting it, then you readjust your shutter, aperture, or ISO to get a good exposure.
Notice previously I said, "good exposure." There are no perfect exposures. You can read the histogram up and down, to the right or left, it doesn't matter. There are two aspects to exposure that you can see right on your camera's LCD: the Histogram and Highlight Clipping or "blinkies" as it is often called.
The Histogram represents exposure. The perfect histogram would touch the left, or black, side and continue in what looks like a mountain range till it touched the right, or white, side of the graph. It is literally a bar graph that helps you decipher what is going in you exposure. The histogram is designed to tell you where your exposure lies in between the two points of white and black. It is based on the Zone System developed by Ansel Adams. He determined that variations of color tone affect exposure and that these variations can be measured and used to get your exposure.
Excerpted from Photographic Lighting by Robert Harrington. Copyright © 2013 AE Publication Ltd. Excerpted by permission of AE Publications Ltd.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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