Lighting

No Strings Attached With
Wireless TTL Flash

Jack Neubart  |  Nov 1, 2001

These first three images illustrate how this tropical bloom is affected by off-camera lighting, with and without fill.
Photos © 2001, Jack Neubart, All Rights Reserved

Multiple-flash lighting is easier than ever with today's dedicated flash technology.

When in Madeira, while working on my Kodak Electronic Flash book (Silver Pixel Press), I found myself photographing a spider and its elaborately fashioned web. The problem was that my subject was several feet away, amid the shrubbery. I had one hand gripping the SLR, the other grasping the dedicated flash, being hampered by the length of the TTL cable connecting the two. Another situation found me uncomfortably ensnared in a mess of cables when using multiple shoe-mount strobes outdoors. Other problems with cable connections are that they can come loose or become frayed, and cables that extend any reasonable distance add bulk and weight to a camera bag.

Wired multiple flash also involves various adapters and time-consuming setup. Moreover, this combination may limit TTL auto operation to some degree (depending on the system). And we haven't even mentioned dealing with dangling cables that get in other people's or your own way. Enter a practical solution: wireless TTL flash.

Wireless flash is not new. It's been around for a long time, employing any of various devices to trigger remote electronic flash units. However, these devices are designed around the use of non-TTL strobes, often relying on manual operation and handheld flash meters to determine and control output. That's well and good for studio flash equipment or whenever you take a more measured approach with portable flash units. Dedicated TTL shoe-mount strobes for today's electronic SLR cameras, on the other hand, now benefit from something simpler, sans wires, to make the process of shooting with multiple off-camera flash flow almost effortlessly.

Wireless TTL Auto Flash
For wireless TTL flash to work, both camera and flash must be designed to support this function, one operating as an extension of the other. Wireless TTL flash usually begins with the camera manufacturer and the dedicated strobes designed for use within a family of high-tech SLR cameras, and may apply solely (or to the fullest degree) to the latest generation within that family. Moreover, for the utmost convenience to the user, the emphasis is on wireless TTL auto flash. The availability of wireless TTL auto flash is not limited to the manufacturer's own products, encompassing a few after-market strobes and even a TTL remote module. Moreover, the camera gear compatible with wireless TTL flash is not limited to autofocus 35mm models. Wireless TTL compatible, dedicated strobes aimed at select models of autofocusing 35mm SLRs may also be suitable for APS, digital, and non-AF 35mm SLRs from the same manufacturer. And some after-market products may also be suitable for TTL-flash-enabled medium format cameras.

This employs the off-camera flash solely, for sidelighting from a high angle (flash handheld). The picture is much more vibrant. (Note: the on-camera flash was set so as not to emit any light, but to trigger the remote unit.)

The Wireless Connection
Wireless TTL flash is not a totally detached association: There must be something attached to the camera to activate the remote, off-camera flash. Depending on the system, that can be the built-in flash or it could be an external flash or signaling device seated in (or connected by way of) the dedicated hot shoe. Yes, even though we're going wireless, the main controlling unit can be attached to the camera's hot shoe by a dedicated adapter and cable, but that would seem to defeat the purpose of a totally wireless system. This cabled rigging, however, might still be needed to get around obstacles that stand in the way of sending signals to the remote flash units. For our purposes, we'll assume an unobstructed signal path that leaves us totally cable-free.

Select wireless-enabled TTL flash units can act as both "transmitter," which sends out an activation signal, and "receiver," which, upon sensing that signal, fires the flash. For this to happen, we obviously need at least two such units employed together, with one serving to transmit the signal, as the "master" unit, the other receiving the signal, as the remote, off-camera "slave" unit. The remote strobe may be said to be "slave-synched" to the first, or simply "slaved." Within the same family of strobes we may find wireless-TTL flash units designed without the ability to act as the master unit, simply serving as the slave flash. This option reduces the cost, and makes sense, since we don't need more than one master strobe, except perhaps as backup.

The Signal
What constitutes a signal? When it comes from the dedicated flash, it is generally a very short burst of light at a pre-defined frequency filtered in the near infrared. To further ensure that it does not contribute to the exposure, this burst of light is emitted prior to the actual exposure, similar to a pre-flash that some TTL systems use to measure the required flash output. The pulsed signal is coded. This coded signal carries all the information both camera and strobe(s) need to communicate back and forth, maintaining full functionality, as if the flash were on-camera and to the degree allowable by the system.
Finally, both units were used, with the diffused on-camera flash bringing out some of the background detail. I won't say which of the last two I prefer. You choose.

Master & Fill
Ordinarily, the master unit is on-camera (unless on a cable and off-camera). When the master unit is a flash, it may serve as a fill light, with the remote (off-camera) flash generally providing the main source of illumination. It may be possible to set the on-camera flash so that no light is emitted, for instance, to prevent glaring reflections in shiny surfaces directly facing the camera, or for more dramatic lighting. Of course, a bounce/swivel head on-camera may alleviate this concern, but then there's the fear that the remote flash will not read a signal that is not beamed directly at it or that some of the indirect light may still reach the subject.

The master unit transmitting the signal does not even have to be another strobe. Sitting in the hot shoe, it can simply be a device that sends out the signal that triggers the slaved strobes, without adding any visible light. In that case it is simply called a "transmitter" or "controller." (Note: the term "controller" may also apply to a device attached to a slaved flash.)

Each system operates according to its own parameters. The system may offer fully automatic TTL flash exposure control, or certain combinations of camera and flash may limit you to manual wireless operation only, or limit you in other respects. There may be other limitations to overall functionality, all varying with the camera and flash. For instance, wireless TTL flash may support such functions as flash exposure compensation, flash bracketing, high-speed sync, and stroboscopic sequential bursts, provided these functions are there to begin with. One of my favorites is the ability to trigger all the strobes simultaneously to emit a modeling light, helping me picture the combined effect of all the lights on a set. You'll have to check the instruction manual for your photo gear to learn the full extent of your system's capabilities.

I keep things around, knowing they'll be useful one day, as is the case with my cat's white plastic medical collar. I used this as a light tent, positioning the miniature kaleidoscope in the center, on a backdrop of Mylar and gold-tone reflective material. To bring out the gem-like stones at the front, I positioned one flash on the right, a second on the left, parallel to the first, with matching output. Each flash was positioned within inches of the tent and aimed so that the light from each strobe hit the tent at a glancing angle, not full force (we're lighting through thin plastic). Hand holding the camera, I poked the lens through the opening. Owing to the highly reflective nature of the kaleidoscope barrel, a distorted reflection is captured, but serves to break up the monotony of the uniform silver finish.

Maintaining The Proper Balance
Now that we're equipped with a camera and two or more flash units supporting wireless TTL auto lighting, we realize one requirement: If we pop all the strobes as is, the lighting may be even, assuming the same model flash, and will almost surely produce multiple shadows. We could overcome this problem by placing the strobes at varying distances, add a diffuser, bounce the light, or set the zooming head manually to respectively different positions--all of which would affect the quality of light.

Another alternative is this: Provided this function is built-in and supported by all the "connected" gear, simply use the on-camera master unit to define a ratio of relative brightness levels that places greater emphasis on one or more lights compared with the other supporting lights. For example, the off-camera key light that provides the defining illumination should produce the defining shadows. So we set the ratio to ensure this result.

Unfortunately, this may not be enough to guarantee that the secondary lights won't be so strong that they cast even a faint shadow. Using the modeling light function helps you visualize the results with your setup, but even then, there are no guarantees--nothing beats a true (incandescent/tungsten) modeling light. Given that, I've found it was still necessary to physically reduce the light output further (using a combination of the methods just outlined), to totally obliterate the uninvited shadows. It may also help to work with flash units of unequal output (higher and lower guide numbers) to begin with.

Where applicable, the degree of ratio control varies with the camera/ flash system, from simply 2:1 to 8:1, controllable within the master unit. This option may extend to a ring flash, albeit on-camera, with a ratio adjustment available between the two flash tubes. The ring flash may further function as the master unit, triggering an off-camera strobe, which may be used to shed some light on the background, for instance, when you want to add an environmental feel to your close-ups.

The system may also be designed to automatically reduce flash output of the on-camera flash when it encounters backlighting (from available light), to produce a more natural rendering with fill flash. That may even extend to the use of an external TTL flash in the hot shoe, with another dedicated flash positioned off-camera and backlighting the subject.

This shoe-mount flash has a switch at the bottom, whereby it can be set to serve as the master/transmitter or slave/receiver unit, or neither. The LCD panel shows the flash is set to a specific channel, the same channel used by the remote transmitter and any other flashes that should fire at the same time. There is also group designation (A or B). The first flash can be designated "A" and the second "B," whereupon the respective amounts each light would contribute to the picture could be set on the ratio scale (which is on the transmitter).

Quiet--I'm Channeling
Routinely a dedicated wireless TTL system gives you a choice of two or more channels. Just as selecting a channel on your TV lets you see only the programming on that channel, selecting a channel on a dedicated flash system tunes each component--the transmitter/master and the receiver/slave--into a signal of a specific frequency. The transmitter sends the triggering signal to any flash attached to or integrated into a receiver locked into the same channel. You can have one or more flashes assigned to one channel, but multiple channels cannot be assigned to the same flash unit.

Why do you need separate channels? You may find that someone else is working with a similar system that is triggering your own--meaning they're set to transmit on the same frequency as your lights. If this happens, you may have to select a different channel for all your flash equipment. Or you yourself may have multiple cameras and strobes set up, and to avoid popping all the lights at the same time, set one (or a group) of flash units on one channel, a second light (or group of lights) on a different channel, and so on, for the remaining available channels and lights. On the face of it, it may be no big deal to pop the strobes at the wrong time, until you realize that the flash you need at the moment is still recycling, or that the batteries have worn down from unnecessary use. Or you may be using a long exposure on a moving subject, and you want a different strobe popping at different intervals to catch different stages of movement.

Also, depending on the system employed, it may be possible to not only set channels, but to assign different strobes to different groups, all firing under the same channel at the same time. For instance, Group A (which could consist of only one light) might be the on-camera strobe serving as fill, with reduced output set on the ratio scale; Group B (again possibly only one light) serves as the off-camera main light. It might also be feasible to position another light or group of lights (Group C) to illuminate the background. You can get more creative and, with the appropriate accessories, set the main light up as an umbrella light to produce a flattering portrait against a painted (Group C illuminated) backdrop. In this case, the fill light will have to be toned down considerably to avoid casting objectionable shadows, since the umbrella light is significantly weakened, as is true of all bounce lighting.

Wireless TTL Flash

Signal Blockers?
Any way you approach it, for it to work correctly, wireless TTL mandates that the remote flash (or more to the point, the receiving sensor) be positioned within a certain distance and at the right angle so that it reads the transmission signal. That's less of a concern indoors or in enclosed environments with reflective surfaces nearby. To test out my system, I even aimed the transmitter at a closed window, from a few feet away, with the slaved flash on a chair, its sensor partially blocked. I still managed to trigger the flash.

Armed with that information, I ventured out to the zoo, only to learn that additional restrictions on flash placement made triggering the off-camera flash (by the on-camera strobe) a tricky proposition. Holding the flash aloft and out of sight in my left hand, I found that a twist of my hand or arm could make the difference between success and failure, since my entire attention was focused not on the flash but on a subject that was often moving. Other situations found me placing the flash on a tabletop tripod on a level shelf outside a glassed-in exhibit. Moving a little too far from the off-camera flash resulted in a loss of triggering signal, apparently resulting from an increased angle. Moving the flash closer to my position made a world of difference. Moreover, indoors, such things as fluorescent lights and cell phones could interfere with the signal, according to one manufacturer. Outdoors, bright light hitting the sensor could be the culprit.

In more open environments, both at the zoo and in a large botanical conservatory, placement of the off-camera light proved even more critical. I had to keep reminding myself to swivel the flash head to ensure the sensor was aimed correctly to read the on-camera flash. With flash recycling often coming so fast, it wasn't possible to check to see that the remote flash fired before it had already recycled. There were times when I simply turned to someone standing nearby and asked if that person wouldn't mind observing and telling me if the off-camera flash had fired. I was relieved to learn that it had.

Alternatives To Wireless TTL Flash
You may own an older strobe or camera, but still want to shoot with multiple-flash setups, sans TTL control. You're in luck: the necessary accessory is practically at hand, ranging from very basic and economical to fairly high tech and expensive. Just remember that this route involves a more studied approach to exposure control, even with auto-sensor flash units, and possibly involving a flash meter when the strobes are used in manual mode. You may also need a standard PC sync socket on the device to be triggered.

The simplest is a photo-optical slave, which attaches to the off-camera flash. These devices come in various sizes--some extremely small. A photo slave is sensitive to visible light, responding to the short bursts emanating from a flash, so that a separate transmitter is not needed. It ordinarily attaches to the X-sync contact on the off-camera flash, in place of the PC sync cord, for non-dedicated operation. Size, cost, and sensitivity generally go hand in hand. Optical slaves are reliable so long as they are in line of sight from the triggering burst of light. Indoors, light bouncing off nearby walls may be enough to trigger the remote flash. Some flash units come with a built-in optical slave sensor, so they can be triggered remotely without additional accessories. The basic drawback to an optical slave is that any strobe, or possibly other blips of light, can trigger it. In contrast, coded infrared slave systems are not triggered willy-nilly by any flash unit or light sources. They may provide such options as channel selection, and are not hampered by obstacles as easily as optical slave sensors.

A radio slave is another alternative, very often used in place of a cable release, to remotely trigger the camera itself along with off-camera flash units, or simply to trigger one or more remote strobes alone. This triggering system comes in handy when the slave unit may be hidden behind obstacles that would otherwise interfere with other wireless options, or where other bursts of light may inadvertently trigger the system. These systems are often the first choice among professionals, for use indoors and out. Strong electrical or electromagnetic fields, however, may disrupt transmission/reception, thereby interfering with overall functionality (which is why pros sometimes need to hardwire their lights). Of these radio remotes, we even found a model with a digital LCD readout and high tech features to match. As with infrared devices, both a transmitter and receiver are required for radio remote operation.

Why Won't My Wireless TTL Slave Flashes Fire?
Each system operates according to its own parameters. The following are generic causes/solutions that may or may not apply in your specific situation.

  • The obvious: are the master/transmitter and slave/receiver units switched on; are the batteries inserted and fresh; are any of the units in standby mode?
  • Does the camera or flash support wireless TTL flash? Only manufacturer-specified combinations work in this mode.
  • Where necessary did you set the receiving units as slaves and the master unit as master; did you attach the slave controller to the slaved flash?
  • If the built-in flash is used to trigger the slave units, is it popped up, in its ready position?
  • If a hot shoe connection is used, is the master unit seated correctly/fully in the hot shoe?
  • If a remote cable is used with the master unit are the connections firmly in place at both ends; is the cable damaged?
  • The units may be recharging--a pre-flash may have inadvertently triggered the slave units, or you simply didn't wait long enough. The master unit also needs time to recharge. Monitor ready lamps on all involved components. If the system signals it's ready by blips from the AF assist beam on the flash, monitor that.
  • There may be some interference. The system is most reliable indoors, where nearby walls can reflect and redirect the signal to the receiver, unless something is blocking it or the outgoing/transmitter signal, or otherwise interfering with the signal. Some systems are subject to interference from such things as nearby fluorescent lights and cell phones. It may also be time to attach a TTL remote cable to the transmitter to try to get around nearby interference, or simply to switch to a TTL cable system all around. Radio remotes and optical slaves may not be usable, unless your camera and strobes have the necessary PC sync socket for conventional flash firing, keeping in mind this bypasses all TTL operations, requiring full manual exposure control and possibly a flash meter.
  • Outdoors, bright light hitting the sensor may interfere with remote triggering on the slave units.
  • Distance--the slave units may be too far from the master/transmitter unit.
  • Angle--the slave sensor is facing the wrong way or the angle exceeds acceptable parameters. If the flash has a swivel head, direct the head at the subject; aim the body (with sensor) at the transmitter on-camera.
  • The wrong channel has been set on the transmitter/master unit or on the receiver/slave unit. Slaved strobes can only respond to a signal on the same channel as set on the mater unit transmitting that signal.

WIRELESS TTL FLASH COMPATIBILITY
The following table lists the cameras, flash units, and accessories that can be used for wireless TTL flash operation. Select camera-flash combinations may permit operation that takes full advantage of the latest advanced technologies incorporated in the camera and flash units, beginning with full TTL auto flash control, whereas others may limit functionality in various ways (see Comments). With certain systems, the built-in flash acts as the master unit, whereas with others, a special transmitter or hot-shoe flash is required (exclusively or as an alternative to the built-in flash) to activate off-camera slaved strobes, which themselves may require a wireless controller.

Manufacturers/Distributors

Brandess-Kalt-Aetna Group, Inc.
(847) 821-0450
fax: (847) 821-5410
www.bkaphoto.com

Calumet Photographic Products
(630) 860-7447
fax: (800) 577-3686
www.calumetphoto.com

Mamiya America Corp.
(914) 347-3300
fax: (914) 347-3309
www.mamiya.com

Omega/Satter
(410) 374-3250
fax: (410) 374-3184
www.omegasatter.com

Phoenix Corporation of America
(516) 764-5890
fax: (516) 764-5970
www.phoenixcorp.com

Quantum Instruments, Inc.
(516) 222-6000
fax: (516) 222-0569
www.qtm.com

R.T.S. Inc.
(631) 242-6801
fax: (631) 242-6808
www.rtsphoto.com

The Tiffen Company
(716) 328-7800
fax: (716) 328-4186
www.tiffen.com

ToCAD America Inc.
(973) 428-9800
fax: (973) 887-2438
www.tocad.com

Vivitar Corporation
(805) 498-7008
fax: (805) 498-5086
www.vivitar.com

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