July 25 2006
Photo by: kazatzka
The Nitty-Gritty: Technical Stuff
Here are some technical terms that will help your flash technique out:
TTL
This is the wonderful invention where the flash actually meters Through The Lens, taking into account the light already in a scene to derive a correct exposure. But, as with normal exposure, you can learn a lot by taking the light into manual mode, either dialing in a manual output such as 1/64th or 1/8th into a professional flash or by using exposure compensation, which uses the default metering but over or underexposes at your whim.
Professional flashes often have even more advanced modes that use quick pre-flashes as a sort of "light sonar," sensing the scene precisely. These names include Canon's E-TTL II and Nikon's i-TTL. In practice, it just works, but you may notice your subjects blinking at the pre-flash.
EV
Exposure Value. This basically is a value that says how much light there is or, when used with exposure compensation, how much light should be added or taken away. The math of it is pretty complicated but it's easy to understand in practice. Every time a scene goes up one EV, it gets twice as bright. So if it goes up three EV, it's (2x2x2)=8 times as bright. Compare that to trying to calcluate that in f-stops, which would be the difference between f/5.6 and f/16 -- EV is much more intuitive.
Guide Numbers
This is a number published with every flash that determines how powerful its maximum output is. It is expressed as subject distance * f-stop value = guide number. These are calculated at particular film speeds -- almost always ISO 100. If you get used to the calculations, it's a sure-fire way to calculate correct exposure. What f-stop should I use if my subject is 10 feet away and I'm using my built-in flash (GN=12) at ISO 100? 10 * x = 12. x = f/1.2 Whoops, either I need to bump up my ISO or I'd better be using a darned fast lens. If I were using a more powerful flash, let's say the Nikon SB800 (GN 125), my value would be f/12.5 -- or the closest usable value, f/13.
Sound scary? The good news is you don't ever have to use any of that if you don't want to -- these days guide numbers mostly serve as a quick guide to how powerful a flash is the higher the number, the more power. But be careful! As you can see, the definition of a guide number includes a unit of distance. American flashes express this in feet; other flashes in meters, so American numbers will be much higher.
Red Eye Problems?
There are a number of ways of dealing with redeye. The first, and generally most effective, way is to move the flash as far away as possible from the lens or point the flash head away from the subject (ie: bounce the light). As noted above, the closer the flash source is to the lens axis the worse redeye is going to be. So if you detach the flash unit from the camera and lift it up in the air a short distance you’re likely to reduce redeye considerably. This is one reason why wedding and news photographers tend to mount their flash units on external metal brackets attached to the camera itself - flash brackets. And bounce flash eliminates redeye by definition.
One drawback with moving the flash, aside from the inconvenience of moving the flash unit, involves low-light photography. When light levels are low the pupil of the eye will dilate to let in more light, just like a lens diaphragm. If you take a photo of a person with flash their irises don’t have enough time to react to the burst of light, so their pupils will remain dilated. The result is a photo of someone with huge pupils, as if they were on drugs.
Another way of reducing redeye (and also minimizing the huge pupil problem) is to have the subject look at a bright light shortly before taking the flash photo. This usually sort of works because the person’s pupils will contract in response to the bright light, reducing the amount of light reflected back from the retina to the camera. For this reason many EOS cameras have bright white lamps built into them which the photographer can illuminate at will.
Source: photonotes
Pre Visualizing
It's often difficult to judge the direction flash illumination will travel and its effect. When is the right time to take the flash off the camera? ...
Keep in mind that we want to imitate the sun and its effect when using flash. The key word here is imitate, not replace. The sun comes from above us, always. This means that shadows should always fall below subjects and not above them. So when using flash, shadows must appear below the subject and not above. There is also just one sun so there should only be one highlight reflected in the eye. With proper technique, multiple flash can be used while maintaining just one highlight.
Excerpted from: The TTL Flash System
Related Links and Information
strobist very advanced, but -- ahem -- illuminating Nikon glossary The Science of It All
Photo by: carpe icthus
Timing is everything
If you stand in the end of a long exposure, just long enough to catch the flash, you can turn yourself into a ghost.
TECHtata
Flash
"Before I learned the art, a punch was just a punch, and a kick, just a kick. After I learned the art, a punch was no longer a punch, a kick, no longer a kick. Now that I understand the art, a punch is just a punch and a kick is just a kick." -- Bruce Lee
Why, you might wonder, would someone lead a column about using flash with a quote about punching and kicking? No, things aren't about to turn violent in Utata-land, but in dealing with thousands of photographers in virtual and actual reality, I have seen a trend of education and exploration that has turned "flash" into a naughty word in many circles:
The beginner photographer with an automatic camera records the world, often with default camera settings that pop a flash only when light is low. The camera does its job, recording memories and scenes, but the results are often pedestrian. Faces are often bleached out and backgrounds are dark indoors, while at daytime the reverse is true -- the scene is bright but the subject is covered in harsh shadows. After trying out new settings and exploring camera functions, our intrepid photographer takes some indoor shots with no flash, and they turn out wonderfully. Her friends have skin tones again! The scenes seem to have depth! Clearly, she thinks, flash is a tool for simple shots. This is the stage where our photographer learns how to use a flash, and sees it for what it is: just another tool in the arsenal of ways to compose great pictures. Maybe, due to constraints or philosophy, she'll take most pictures without flash, but when the time comes that it would improve a picture, she'll be unafraid to use it.
The aim of this article is to bring us all to stage three. For purposes of fitting relevant information into less than 50,000 words, we will restrict this article to using on-camera flash -- either the flash that comes on the body of nearly all point-and-shoot cameras and all but the fanciest dSLRs, or the external flashes that fit on your camera's hot-shoe (if it has one), such as the Canon 430EX or the Nikon SB-600. For information on advanced flash techniques using multiple flashes, or the big, free-standing strobes often used in studio photography, a good resource is the Flickr group Strobist.
Photo by Ryan Brenizer
Flash: The Light That Isn't There
A flash is simply a way that camera-makers answer the age-old photographer's problem: "I wish I had more light!" In the old days, photographers had to go to great lengths for this, burning magnesium powder, but now we have electronic flashes that fire quickly, can take into account the amount of light in the scene, and are much less likely to set fire to you.
Light is literally everything in photography, and understanding the way it works will improve your photographs dramatically, if not the way you see the world. The Exposure TECHtata is invaluable to you here in understanding many of the basics. Technically, flash light is no different from any other light, but there are a few particulars to keep in mind:
It's momentary
A big part of what makes using flash difficult is that the light that will end up in the picture isn't there when you're composing the scene. Using flash correctly thus requires more pre-visualization and trial-and-error than available light photography -- but the low per-shot cost and LCD review of digital photography help the trial-and-errer greatly. Some professional flashes offer "modeling lights" that put out a low-power steady beam to give you some idea of how the scene will look, but this is generally only useful for very still scenes such as product shots and botanical macros.It's powerful
Even small flashes tend to be more powerful than other indoor light, which we know by the thousands of purple spots we've had lingering in our eyes over the years when our picture was taken. This has endless applications -- need a smaller aperture, letting in less light for a wider area of focus? Flash is your friend.It's concentrated
And from a single source. This sounds simple, but can cause most of the problems that makes people hate flash so much. Virtually all light sources follow an inverse square law of light fall-off. This sounds incredibly complicated, but all it means is that exposures will get exponentially darker as you move the subject away from the flash -- so if you move them twice as far, they will get 1/4th as much light, and if you move them 4 times as far, they will only get 1/16th. This is why when you use a fast shutter speed and flash to expose a subject indoors, the room behind them is almost totally black. We don't often think about this with our primary light source -- the sun -- because proportionally speaking we are all more or less exactly the same distance from the sun. But even that big ol' ball follows the law. Just ask Pluto.
What Can I Do to Make my Flash Work Better?
Keep in mind that these are things to try, not rules. While they will often improve your pictures, sometimes another way will work better. Just shoot, shoot, shoot, and keep trying new things.
Nor, of course, are these the only ways to make your flash work better. Once you get comfortable with your flash, you'll find that it's an imaging tool in the same way that your camera is -- which means that it's ripe to show the world your personal expression and style. Is your envisioned world awash in soft light? Is it filled with sharp angles and long shadows? Does your vision include crisp images, a slice of time, or is the passage of time simply another element floating about your scene? Or all of the above? There is no right answer, only the one you work out for your own vision.
Use Your Flash When It's Bright Out
This is the first way that flash use can be a little strange -- it's often most useful when you have more than enough light already. This technique, called fill-flash uses the light of the flash to fill in the shadows that often appear in mid-day sun. Any camera with a flash can try this -- on point-and-shoots it's usually indicated by a little lighting bolt button or menu item. As a bonus, if it's a little darker than mid-day or you have a camera that can use flash at high shutter speeds or small apertures (generally speaking, dSLRs), you can use flash in conjunction with manual exposure settings to properly expose your subject while slightly underexposing the world behind her, making for a dramatic effect as shown in the example to the right.
Use Your Flash With Slower Shutter Speeds
Photo by: carpe icthus
On more advanced cameras, flash can be used while manually dialing in the shutter speed. On many others, the camera will do this for you in "night portrait" mode. This can do two things: First, in darker situations, this will help you expose the background so that your subjects don't look like bright faces against a black backdrop. The exposure, of course, can also be helped by higher ISO speeds and wider apertures. I do this constantly; the picture to the right is an example at ISO 1400 and f/2.8.
Photo by: bikeracer
Second, remember that flash is momentary -- it often fires at a speed faster than camera shutters can, such as 1/50,000th of a second or less. This is how the ubiquitous water-drop pictures are captured as in the image to the right. When the shutter is slow enough to allow motion blur, the quick snap of flash light acts as a second shutter -- leaving a sharp image superimposed over blur. When used correctly, this can create a cool effect -- it captures the scene but leaves a sense of motion.
If possible, when using this method you want to select "rear-curtain" shutter, a fancy way of saying get the flash to fire at the *end* of an exposure instead of the beginning, so your subject's motion is captured appropriately. A proficient user of this is photoblogger and Flickr user Nikola Tamindzic. Be careful: this link is safe for work, but his general site is nowhere close to it. One last trick: If you stand in the end of a long exposure, just long enough to catch the flash, you can turn yourself into a ghost as shown in the image to the left.
Bounce Your Flash
This is my favorite thing about using flash
Do your flashed subjects look like vampires (red eyes, bleached skin)? That's because you're firing the flash directly at them, which is bouncing right back into your lens. If you have an external flash that flips or the rare point-and-shoot with a bounce setting, like the Leica Digilux 2, you can get the light to bounce off an object, such as a low ceiling, before it hits your subject. This does a few things that usually make for more attractive pictures:
It makes your light diffuse and soft. Remember that inverse square law? It will have a lot less effect if you take into account the distance to the ceiling and back, as your subjects will be a more similar distance away from the light source. Put 1 and 2 together and you get something like the figure below. It doesn't blind your subjects and anger your friends by firing a big ol' light into their eyes, and they will be more at ease around you.
Photo by: carpe icthus
If you have a camera with a hot-shoe, it is a huge advantage to get a flash that can swivel as well as tilt -- this allows you to bounce when the camera is vertical, and allows one of my favorite tricks with low ceilings: bouncing slightly backwards.
Have fun with this! Whenever I enter a room with a flash, I immediately look up. How far up is the ceiling? What color is it? (the light will pick up the color as it bounces) Where are the walls? I think of it as a big billiard game of light.
Questions, Comments, Discussion
On July 27 2006 Nancy/nuanc said ...
thanks so much for the very helpful article. It's somehow comforting to know that I'm right on the track that most photographers go through - and at stage 3 no less!
On August 01 2006 btezra said ...
~I am not much of a fan of the flash, I do prefer natural light, fast lenses, but I have shot a bit lately with external/attached flash units on both Canon and Nikon models and have ben amazed at the results I got...especially when using a small soft box attachment and the Lightspehere product...I suppose it all comes down to what you are comfy with while shooting, and what matter most to me is shooting on the street and I hate to intimidate or freak out a subject on the street with a big mean flash, but, when indoors and in tough lighting a flash can make or break a shot~
On August 14 2006 Andrei Lintu said ...
If you want to go even further with flash usage (off camera), in order to get even better results, this is a very good place to start:
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