Flash Guide Numbers

Once upon a time, when the earth was young, photographers determined proper flash exposures using a quaint concept called the Guide Number. It was a relatively simple concept based on several known constants: One was the relationship between brightness and distance called Inverse Square Law, and the other was the numerical relationship between the values assigned to the lens aperture size, called an F-Stop.

Arthur Fellig, whose nom de guerre was Weegee, was pretty typical of the on-camera flash shooters of the day. His equipment was pretty typical of the time: A 4 x 5" Speed Graphic with a flash "gun" that fired single-use flash bulbs. Based on my personal experience (my Father used a Speed Graphic) the cylindrical handle housed 3 flashlight batteries that produced the "oomph" necessary to light the flashbulb and power the solenoid that would physically trip the shutter. The flashgun employed a regulator that could retard the shutter until the discharge from the flashbulb reached its peak output. In use, these photographers were determining their own guide numbers based on the comparison of negatives made with a single size of flashbulb and a specific shutter speed at a specific distance while using a series of different F-Stops. Once an optimal F-Stop was determined, final adjustments were made to the amount of retard necessary to tweak the exposure even further. This process had to be repeated for each shutter speed when flash bulbs were being used, since they behaved more like continuous light sources. The equipment was temperamental, so once you got everything adjusted to your liking, you left it alone.

In actual practice, the photographer loaded his camera with film and flashbulb and set the lens aperture his experiments deemed best. When his subject arrived on the scene, he would wait until the distance between his camera and the subject was the same as the one determined during his exposure tests, and trip the solenoid the make the photo.

The availability of the electronic flash simplified the calibration process, but didn't eliminate it. The instantaneous nature of electronic flash exposure made the shutter retardation unnecessary, so long as the flash fired when the shutter exposed the entire surface of the film. You now had some flexibility in your choice of shutter speeds, but you still had to determine a working guide number, since none was provided by the manufacture. The literature might give some suggestions of where to start, but more often that not, the photographer was on his own. This photo of a Heiland Flash illustrates how some of these early units looked. Sorry, eBay: It was the best photo I could find.

Fast forward to the more modern times. Gone is the Speed Graphic. Flash units are powered by compact AA batteries. Each flash is given a Guide Number by the manufacturer. One such number was assigned to each ISO, and could be calibrated in feet, or in meters. Most flashes had some sort of scale (linear or circular) that allow you to select the ISO of your chosen film, and read, from the scale, the proper F-Stop for the desired distance. For example, a typical guide number for an ISO 100 film used with a typical single output, 4-AA cell flash would be 110. In use, one would set the camera to F11 if the flash to subject distance was 10 feet. Based on this single Guide Number, we can extrapolate the following:

5 feet	7.5 feet	10 feet	15 feet	20 feet
F 22	F 16	F 11	F 8	F 5.6

Now these values are approximate because the environment contributes to the efficiency of the flash. Making photographs in a small room with white walls will require different settings from a large, all black venue. During the dark ages, you might keep an notebook listing your experiences in different environments, or you might consider getting a flash meter. Perhaps it was the purchase of my first flash meter, a Wein WP500, that gave me confidence in working with flash. Click here to follow the Adorama link where I obtained this photo. I paid $34.95 back in the early 1970's which was considered incredibly reasonable at the time.

In the digital age,You don't need to take the guide number on faith. If you have a tape measure, you can simply set your flash at exactly 10 feet from your subject and shot test shots at a variety of aperture settings until you find the exposure that is right for the environment. If it turns out that your optimal aperture is 8.0, your new calculated guide number would be 80 instead of the optimistic 110 cited earlier. This is so much easier than shooting during the film days, when you'd make photos using transparencies (slides) at a variety of apertures and evaluating the results after they were processed. Once again, you had to be mindful of your environment, as the presence, or absence, of reflective walls or ceilings would shift the guide number up or down, respectively. If I were to re-build the guide number table based on these actual exposures, it would look like this:

5 feet	7.5 feet	10 feet	15 feet	20 feet
F 16	F 11	F 8.0	F 5.6	F 4.0

Synchro Sunlight: One challenge to outdoor lighting is trying to bring the details to the shadow areas of your photograph. Synchro Sunlight is the term used to describe the situation where you attempted to match your flash output to that of direct sunlight. Based on the Sunny Sixteen Rule, the proper front-lit exposure in bright sunlight with and ISO setting of 100 would be 1/200 at F11. By checking the chart, I find that my flash must be place 7.5 feet from my subject to match the brightness level of the sun. If I were to follow the example set my Weegie and his ilk, I would make sure that I always stood exactly 7.5 feet from my subject when my flash was camera mounted. This is somewhat oversimplified, since following this recipe to the letter will probably result in overexposed highlights and unrealistically bright shadows, so you'll need to use your judgement on your actual settings.

In actual practice, you could mount you flash on a light stand place at the desired distance and trigger it using a long cable or an optical or a radio trigger. So long as the distance remains constant, you can be assured of consistent exposures so long as you give your flash enough time to properly re-cycle. An important caveat is that guide numbers provided by the manufacturer are usually very optimistic, since they are often based on exposures in small, enclosed environments. When you bring your lights out into the open, expect some major light loss.

That was lot of writing to conclude that the current crop of automated, through the lens controlled flashes side step a mountain of work, and often yield a high percentage of properly exposed images. But if you are forced to rely on non-iTTL flashes, you would be wise to keep these fundamentals in mind.

Everything Isn’t Black and White

Garry Winogrand: I was at the premier retrospective showing of Garry Winogrand, a noted photographer and chronicler of life in the 70’s. He was one of many photographers who drew their inspiration from life on the street. From the lurid to the mundane, the photos represented a melding of a photographer's observation, timing, and technical competence. The exhibition included prints made from film that was never processed in Winogrand’s lifetime, making this retrospective quite unique.

In a discussion with my editor, she posed a question concerning street photography. She posed that a person with an iPhone could just as easily want the streets of a major city, snapping random images, converting the digital images to black and white, and would achieve results similar to Winogrand’s. On first glance this is entirely true, but if you compare “then” with “now” the answer to the question is much more complicated.
Let’s take the equipment. While I don’t know for a fact, the camera of choice was the black Leica rangefinder camera. This camera was totally manual with no electronics at all. Focusing was done by using a built-in coincident rangefinder (focus was achieved by juxtaposing two images atop one another) and could be used only if you actually held the camera to your face. Exposure settings, aperture and shutter speed, were also set manually, and the adjustment dials could only be seen when the camera was held at waist level. The actual aperture/shutter speed pairing would be determined by a hand held light meter, or in some cases using an adjustment to the Sunny Sixteen Rule. And lastly, the film in the camera had to be advanced manually after each exposure, meaning that even the fastest photographer could only squeeze of one frame ever second, if that.

The modern digital camera literally sidesteps all of these shortcomings. save two. At what physical location is the camera positioned, and at what precise moment will the exposure be made? Both are the domain of the person holding the camera. Perhaps the photographer brings a bit of restraint to the act of photography because he or she will determine when proper focus has been achieved, and at what exact moment the image will be captured. In short, the single most important influence in the photographic process is the experience that the photographer brings to the photographic moment.

In this classic Winogrand image, it is very obvious that a great deal of planning went into this image.  What exposure settings to use, where to stand, , where to place the plane of focus, and when to press the shutter are all decisions that the photographer had to make. A modern digital camera could only address exposure, and even that would be a guess. It is doubtful that this was a random grab shot. It is more likely that Winogrand felt that something was about to happen, positioned himself, adjusted his camera, and waited.


Street Photography: So much of the street photography genre is presented in black in white for a variety of reasons. First and foremost is the fact that the black and white film of the day was far more sensitive to light than color film. This increased sensitivity, reflected in high ASA/ISO ratings, allowed photographers to work in areas that were too dark for satisfactory color photography. This is perhaps the genesis for the available light movement, where only light sources available in the environment could be used.

As an experiment, I purposely printed to opening image without color in an attempt to simulate how the photo might have looked if Winnogrand had taken it. Notice that the viewer's  facial tones are washed out, while the images on the wall, particularly the one with the young woman, become much more prominent to the view. The direction and nature of the existing light worked against me, making the human subjects flat and devoid of any strong sense of three dimensionality.

Making Sense Of The Abstraction: Black and white images are actually abstractions, initially based on an actual physical subject. Through the limitations (or strengths) of the photographic process, the world is re-interpreted in terms of brightness and contrast. forcing the viewer to re-interpret the image in those terms. We become much more aware of form, the interplay between highlight and shadow that gives us the illusion of three dimensions. But without the distractions of color, the view is free to form a different interpretation of the photo's content. 

Let's take a closer look at one of the images from the opening photo, found here. Without color, the viewer must interpret the image through other means. The gaze of  they young woman, her quaffed hair, the apparent smoothness of here skin, the twinkle of the champagne glasses, and the obvious admiration of her companion, force the viewer to draw some intellectual conclusions about what is happening. A New Year's Eve party? A night club scene? What are they toasting to? 

Mood Vs. Situation: I believe that without color, we are not drawn into the mood of the photo. Instead, we are drawn into the situation. And like an abstract painting, the viewer is free to interpret the image any way he chooses. I think that when we see a black and white image, we are initially challenged to interpret the image based on visible shapes and an implied sense of form. This incomplete interpretation of the image allows the viewer to re-assemble the recognizable elements, minus the emotional contributions of color. I believe this explains our fascination with black and white photos, especially those that might appear commonplace at first, but after analysis and re-assembly, provides us with short phrases that give us the freedom to write our own story. It is McLuhan's ultimate Cool Medium.

The fascination with black and white photography goes far beyond the relatively simplicity of processing. It truly is a whole new way of seeing things, as it forces the mind the re-assemble visual scraps into a new "whole". I believe that color is the binder that allows the image to adhere to the subconscious. Without it, an entirely different interpretation is required.

Staying On Top: Nikon's Creative Lighting System

Getting Serious: In the world of Nikon speedlights, there are two schools of thought, manual or iTTL, each championed by one of two gurus. For the manual school, David Hobby carries the banner, while the iTTL advocates seek out Joe McNally for spiritual guidance. While they kid each other mercilessly, they do agree on one thing: a professional photographer must master both. You just have to be prepared when the "wheels fall off", and you're forced to resort to Plan B to get the project on track.

I admit to being a slow learner. I have relied heavily on iTTL along with the Nikon Creative Lighting System (CLS) when on assignment. Even with my lowly D70 cameras, the built-in flash can serve as a Commander for a speedlight (or more) set to receive signals on Channel 3 and Group A. This allows a single speedlight (I usually carry only one in the D70 bag) to be used remotely, off camera, if needed. Often this takes the form of my single SB-800 mounted on a monopod, with or without a light modifier of some sort. Come to think of it, there is also a SU-800 dedicated remote buried deep in the bag would I need more channels and more groups.

The assignment was to show two subjects discussing a floral arrangement. Because it was a pre-event shot, a finished product might have been illogical. But a shot of the two discussing the event, with a hint to their roles in that event, would probably do the trick.

The photo that appears at the top of this post is pretty straight forward in approach and technique. This sketch shot was taken at the highest possible flash sync speed to determine the background (street) exposure, which also gives me the widest corresponding aperture. When shooting indoors, I use aperture priority because I really don't know where the shutter speed will wind up. Outdoors, I resort to the Sunny Sixteen Rule. Once the exposure was determined, I would use flash to raise the inside level of illumination closer to that on the outside.

I have a great deal of confidence in the Nikon’s Speedlight System. When it works, it almost always produces well exposed images. Using simple adjustments from the controller speedlight mounted on the hot shoe, one can instantly adjust highlight and shadow detail by increasing or decreasing the power output of the different flash groups. And feedback is nearly instantaneous due to the previews that digital imaging provides. A nearly perfect system. Until it goes wrong.

The Setup: Initially, I set one speedlight, set to Group C, on the rear of the work table to throw some light onto the back wall to “loosen up” the underexposed areas in the rear of the photo. Next, a light stand mounted SB-800, set to Group A, was aimed where my subjects would be standing. The light was “modified” by shooting it through a Zumbrella. I purposely “choked up” on the umbrella shaft to insure that no light slipped past the Zumbrella’s edges and create a hot spot at the lower edge of the photo. I also pitch it up slightly to feather the light away from the flowers in the foreground. At first the umbrella was to camera left, and by design, the sensor eye on the flash was conveniently pointed directly at the camera mounted commander flash, which would also serve as fill.

Lighting Two Faces: The two subjects were posed, side by side, at a 90 degree orientation to each other. Kay, at camera right, was looking down into the open book she held, and Karen, standing at camera left, was looking Kay. This setup is not ideal because the lighting cannot compliment both faces at once. With my Zumbrella key light on my left, Karen’s face was partially in shadow, lit only by the fill. Kay, on the other hand, had the light perfectly aligned with her nose. Since the photo had to provide frontal exposure on both of their faces, I moved the light to my right side. This evened out the light distribution on the two faces, but introduced a double-handful of trouble.

My Oops Moment: First, by moving the light to my right, I had to re-arrange my speedlight so the body-mounted sensor eye faced the on-camera commander. The Nikon SB-800 does many things very well, but has some limits on rotation. The head can be rotated 180 degrees counterclockwise, but only 90 degrees clockwise. When I rotated the head and the body, I found that the sensor eye couldn’t quite rotate to a direct line of sight with the command. I started getting failures to fire because the sensor wasn’t seeing the controller. This wasn’t apparent until I started checking the images and saw that the key light was not firing consistently. I decided to back up slightly and continue shooting. This solved the flash problem, but because of the close quarters, completely changed the perspective.  These re-adjustments took time, something I was quickly running out of. Once I was back in control,  the composition, the expressions, and the lighting fell into place, and the photo made.

Remember For Next Time: Looking back, there were many things I could have done to get the project moving sooner and smoother. Here are some things I could have done.

• Turn On The Sound Monitor: Remote Nikon Speedlights can be programmed to “beep” when they have returned to full power after flashing. Some years back, I turned all of my lights to “off” when the beep was being pick up by tape recorders during a musical performance.  Had I thought to turn this feature back on, the beep would have told me that the flash actually fired.
• Test The Speedlights: There is a Flash Test Button on the back of the SB-800. When acting as a commander, the Test Button will fire the flash groups (A, B, and C) in sequence. If a flash fails to fire, you’ll know.
• Flash Value Lock: This feature is available on the mid to upper tier Nikon bodies. It is a programmable function of the AE-L/AF-L Function (Auto Exposure Lock/Auto Focus Lock). By setting this function to FV-Lock (Flash Value), you take one flash reading by pressing the button on the back of the camera. The command remembers the correct flash output for each group which allows you to move about without change the speedlight output. Once this information is stored, the flash no longer needs to send a pre-flash. This seems to help with subjects who are “blinkers” because there is only one pre-flash instead of the multiple flash dialogue that accompanies every normal flash exposure under the CLS system.

Things went sideways when I lost line-of-sight contact between the on-camera commander and the remote flashes. Obviously, things returned to normal when contact was reestablished, but that breakdown took a long time to detect. These three steps will certainly help to let me know when things aren't working, since you won't tell what's going on until you stop and check the back of the camera. Remember too, that the introduction of your subjects onto the "set" may interfere with the communication between the controller and remote units, so be sure to test before, and during, the shoot. I plan on having a future post on Flash Value Lock. It appears to not be an option in the D40 clan of entry-level Nikon DSLR bodies. But the ability to lock in a flash value once and being able to change shooting positions and compositions has a lot of potential for overcoming some vexing flash exposure issues. More to come.