we were having a discussion similar to this on digitaldiver a couple of weeks ago:
http://www.digitaldiver.net/yabbse/index.p...;threadid=18167
the following is one of my posts to that thread, discussing an Inon D 180 along with a Fuji E 900:
Advanced Cancel Circuitry (ACC) was designed to increase camera battery life and to speed up the camera's flash recycle time.
The default setting on your strobe has ACC activated. In other words you do not have to take any actions to activate the system. You only have to take an action, in this case installing a magnet, to deactivate the system. The system was designed for cameras that emit a preflash. A preflash aids the camera in determining exposure. Your camera, the Fuji E 900, emits a single preflash and therefore has the ability to take advantage of Advanced Cancel Circuitry. If however your camera did not emit a preflash, such as the Fuji 810, you must shut off the ACC. To shut off ACC, you must install the magnet into the strobe.
As you read this explanation of ACC, keep in mind that the camera's onboard flash is blocked from influencing the actual composition. The E 900 onboard flash's responsibility is only in sending optical signals to fire to the external Inon strobe.
ACC "magnifies" the preflash.
When ACC is activated, the Inon strobe "replaces" the relatively "less intense preflash pulse" with an artificially "magnified blast" of preflash light of its own. The camera sensor detects the "magnified blast" and calculates the exposure with that information. The camera is fooled into thinking that there is much more light present in the composition. Since the camera now feels there's a significant amount of light present due to the feedback it received from its sensor, it commands its own onboard flash to emit a much smaller amount of strobe energy for the main shutter event.
Less onboard flash energy emitted, less camera battery energy used. Shorter onboard flash duration, quicker recycle time for camera's flash to recharge equals quicker turnaround time for next image capture.
When you set the strobe to S-TTL, the Advanced Cancel Circuitry is automatically deactivated.
references:
http://www.inonamerica.com/content/docs/Ad...ircuit2F375.pdf
http://www.digitaldiver.net/lib_docs/D180Manual_1.10.pdf
hth,
b
and also:
Q. When is ACC beneficial?
A. Two Strobe Output Control Modes can benefit from ACC. External Auto and Manual.
In both strobe output control modes mentioned above, the camera is not responsible for the strobe exposure calculations. In manual mode, the user decides how much light the strobe will influence the composition. In External Auto, the user matches the aperture value of the strobe with that of the lens. In external auto, the user may also make minor user defined adjustments to control the strobe's output.
Since the user is responsible for ultimate control of the strobe's output in both control modes above, the role of the camera's preflash is somewhat circumvented.
Originally the preflash was created to aid the camera in determining exposure. By sending out a known quantity of light during the preflash event, the camera's brain could then determine how much strobe light to emit for the main event by analyzing the amount of reflected light it received by its sensor originating from the preflash.
But again, since External Auto and Manual strobe control modes do not require the camera to make that decision, the preflash function is somewhat negated.
With the implementation of ACC, Inon techs found a way to take advantage of the preflash system. At least manipulate it. First remember that the onboard flash is blocked from actually influencing the composition. iow, it really doesn't matter how bright or dim the actual light is emanating from the onboard flash as long as the sensor of the Inon strobe can detect it for firing signals.
What tends to happen in a typical scenario with a preflash camera underwater is that the tiny onboard flash emits a preflash originally intended to pass through air and not water. Relatively speaking, a very small amount of that preflash light makes its way back to the camera sensor for calculating the amount of strobe power needed for the actual image capture. Because of this, the camera then commands its onboard flash to emit a full dump of light. This taxes both the camera's battery and the amount of time it takes the flash to recharge. The result is a waste of time and energy.
Inon techs designed their strobe's circuitry to emit a much more powerful blast of light once it receives the preflash trigger. Because the camera now sees a relatively powerful blast of light being reflected back to its sensor, it in turn directs its onboard flash now to emit a much smaller burst of light during the actual shutter event, once again, saving battery energy and time in onboard flash recycling.
S-TTL:
When the strobe is set to S-TTL, ACC is automatically deactivated. Doesn't matter if the magnet is in or out.
hth,
b
