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Konica Minolta / Sony DSLR Wireless Flash Facts
Minolta's groundbreaking wireless flash system was first introduced in the early 1990's. And a direct descendant of that system, originally designed for autofocus film cameras, was and still is employed in all the DSLRs and wireless flashes later produced by Konica Minolta and Sony. But strangely, all three companies have done a poor job promoting an appreciation for, and understanding of, their invention. There has been much mystery and confusion about how it all works, which could easily have been avoided with just a little more care in creating the product user manuals. I hope to address that here with a handful of essential facts that curious photographers should know about our wireless flash system as implemented in DSLRs - practical information that should answer some persistent questions and eliminate some lingering misconceptions. This information should apply whenever using the built-in wireless flash system of any Konica Minolta or Sony DSLR available to date in conjunction with the Minolta 5600HS (D), 3600HS (D), Sony HVL-F60M, F58AM, F56AM, F43AM/F43M, F42AM, F36AM, F32M, or F20AM/F20M (those last two models can function on some cameras as a controller, but not as a remote flash). [Note: With cameras that have no onboard flash, wireless operation can only be implemented with the HVL-F60M, F58AM, F43AM/F43M, or F20AM/F20M as the controller.]
This is definitely not a complete and detailed technical explanation of the system! Rather, readers should think of this as just a couple of pages that Minolta and its successors neglected to include in their camera and flash user manuals. It's basic but useful knowledge about how the products behave.
Speaking of user manuals, I'm going to assume that you have already read yours - for both camera and flash - front to back, at least a couple of times. If you haven't, then you're probably either not yet informed enough to benefit from what you find here, or you're far too smart to need it! I won't attempt to explain the details of guide numbers, off-the-film metering, flash synchronization with focal plane shutters, optical flash triggers, HSS, or a few other relevant things that I hope you already know about and understand.
So, here we go...
1. The most common way to control the wireless flash system is with the camera's onboard flash. [You can also use the Sony HVL-F60M, F58AM, or F43AM/F43M attached to the A99/A900/A850/A77/A700/A65/A58/A57/A37 or the HVL-F20AM/F20M attached to any of those models other than the A700]. Other Minolta shoe mounted flash units cannot be used as controllers, and neither can the Minolta Wireless Remote Flash Controller. Those configurations work only with Minolta film cameras.
2. When used as a wireless controller, the onboard flash always fires at least three times. It fires a metering burst just before the exposure; a control burst immediately afterwards; and a sync burst during the exposure (with one exception regarding High Speed Sync or HSS, described later). These low-power bursts consist of multiple short pulses that the remote flashes understand as instructions. The three bursts are usually perceived as one continuous flash since they're so brief and close together; but they are separate. (In addition, the onboard flash may also illuminate several times prior to the metering burst to assist with autofocusing or red-eye reduction; but those features are not part of the wireless flash system.)
3. The purpose of the metering burst is to obtain a meter reading of the scene. The onboard flash sends a burst instructing the remote flashes to fire a pre-flash at a specified intensity. Any remote flash set to manual mode will ignore this command. The camera's metering system then reads the light reflected by the scene and calculates what the intensity of the remote flashes would need to be in order to produce the correct exposure.
4. The purpose of the control burst is to communicate the results of the exposure calculation to the remote flashes. The control burst immediately follows the metering burst. It consists of a command telling all remote flashes at what intensity, or duration, they will fire when the final exposure is made. Any remote flash set to manual mode ignores the command and will instead fire at the intensity set on its control panel.
5. The metering and control bursts cannot be disabled when the camera is in wireless mode. This is true even if all remote flashes are set to manual mode, making the metering and control bursts totally unnecessary. This can cause difficulties, and it's an unfortunate design flaw. See the section below on Pre-Flash Problems for more details.
6. The purpose of the sync burst is to finally trigger the remote flashes to fire. The remote flashes will only fire in response to this special burst from the controller - they will not respond to a burst from a generic flash unit. In normal operation the sync burst occurs when the shutter is fully open. In HSS mode the sync burst occurs just before the first shutter blade begins to open.
7. A natural consequence of the sync burst is that it may add some light to the scene during the exposure. My tests suggest that the power of the sync burst is roughly equal to a guide number of...
KM5D and KM7D: 2 (in meters) or 6 (in feet) at ISO 100
Sony A55 and A77: 1 (in meters) or 3 (in feet) at ISO 100
The intensity is not affected by camera settings such as the flash compensation level. Whether or not this light will visibly influence the image is dependent on many factors including aperture, ISO setting, subject distance and reflectivity, ambient light conditions, remote flash positioning and intensity, and shutter speed, specifically in the case of HSS. In most typical situations the visible light added by the onboard flash is of little or no consequence, and it can often be beneficial.
8. In those cases where light from the sync burst is objectionable, it is possible to reduce its intensity. This can be done by filtering, diffusing, or deflecting the output. A filtering material that reduces or blocks visible light but passes infrared light should work particularly well, because the sync signal can be sensed by the remote flashes in the infrared spectrum. Unexposed developed transparency film is one such material; so a completely black 35mm slide placed in front of the flash works well for this purpose. Only experimentation with specific setups can determine how much the intensity can be reduced with diffusing or deflecting techniques before the sync burst becomes too weak to be received by the remote flashes.
In addition, the relative illumination provided by the flash controller compared to the remote flash(es) can be adjusted by changing the aperture and/or ISO settings. To reduce its relative output, use smaller apertures and/or lower ISOs and/or greater subject distances. To increase its relative output, use larger apertures and/or higher ISOs and/or shorter subject distances. The illumination from the remote flash(es) can then be readjusted if necessary using manual output settings or autoflash compensation. This can even be considered a limited form of ratio flash.
9. The sync burst behaves a little differently with HSS. When HSS is activated and the shutter speed is faster than the camera's normal flash sync speed, the entire sync burst begins and ends just before the first shutter blade starts to open. In this situation the onboard flash contributes no visible light to the exposed image. So, if you want to prevent the onboard flash from contributing any light to the exposure, set the remote flash to HSS mode. Then set the camera to M or S mode and select a shutter speed that is higher than the normal sync speed. HSS will engage at 1/200 second with most Alpha models, but some may require only 1/160 second and others may require 1/250 second or faster.
10. Any number of remote flashes can be used, in either automatic or manual mode. The system is not aware of how many remote flashes are being used; and the remote flashes are not aware of one another. Only those flashes set to automatic mode will respond to the metering and control bursts. Flashes set to manual mode are disengaged from the metering system but will still fire in response to the sync burst. Note that the 3600HS (D), F36AM and F20AM/F20M do not have a manual mode option. They always operate in automatic mode.
11. The traditional automatic ratio feature of Minolta's flash system works only in conjunction with film cameras. This function requires real-time off-the-film flash metering, which the DSLRs cannot provide. Ratio effects can still be accomplished with two or more remote flashes by positioning them at different distances from the subject or by setting them to different power levels using their manual modes. [Note: A new and differently implemented ratio feature is available when using the HVL-F60M, HVL-F58AM or F43AM/F43M as a controller with the A99/A900/A850/A700/A77/A65/A58/A57/A37. This is described in the flash user manuals and on Michael Hohner's site.]
(In this section I'll refer to the combined metering and control bursts as the 'pre-flash'.)
As mentioned earlier, the onboard pre-flash cannot be disabled in wireless mode. This can lead to at least two types of problems. First, if you're photographing people or animals, the pre-flash can cause them to blink. Then, since the actual exposure typically follows the pre-flash within a fraction of a second, the photograph will often catch your subjects in mid-blink. Second, the pre-flash makes it difficult to work with generic flash units that use optical slave triggers. Standard optical sensors will fire their flashes in response to the pre-flash, which is too early. Then, when the sync burst occurs a fraction of a second later during the exposure, there will be no light from those units.
There are some workarounds that might help with these problems. The first is to use your remote flashes in manual mode rather than automatic. That way you'll only have to deal with the pre-flash from the camera. And you can try reducing the intensity of the onboard pre-flash as described in #8 above - particularly if you use an infrared filter that blocks most or all of the visible light. Another option with some Alpha bodies (the ones that have a moving mirror) is to use the camera's two-second shutter delay. The pre-flash will still occur, but your subjects' blinking eyes and/or your remote generic flash units will have two seconds to recover from it.
Because of these issues, if you frequently do portraiture or want to work with standard remote flash equipment you may need to look into different approaches using generic lighting solutions such as radio frequency remote flash triggers. Unfortunately, these will be an added expense and in most cases will negate the inherent benefits of the built-in wireless system such as TTL autoexposure and HSS.
That's it, for now. Short and sweet! However, I plan to expand on this at least a bit with more details about the most common types of problems encountered with the system, and some effective solutions for them.
A final note: My personal testing has been done using only the 5D/7D/A55/A77 cameras and 5600HS(D) flash, but I've confirmed everything here as best I can using information from numerous sources and documentation available for all KM/Sony DSLRs and wireless flash units. If you have different information regarding any of the other cameras or flashes, please let me know.
Text and images © 2008-2017 Ray Lemieux