The Pentax Optical Slave Modes

I am now working on further reviews and updates to my Guide for Pentax Flash ('The Pentax Digital Camera Flash Lighting System), which is currently on the 2nd edition. I am not planning to issue an entire new edition yet, but rather a supplement document with the new material, to go alongside the current Guide version. Eventually I will converge the two plus anything new, and corrections to the existing Guide, into a new Third Edition. But that is likely to be next year. For now I hope to be able to issue a supplement document by the end of this year.

There are a number of new areas I plan to cover, including this topic here, the Optical Slave Modes. Ultimately this new material will be added to the existing Guide, Section 11, 'Wireless (Off-Camera) Flash Operations'. I'm showing here the text for this new material on the Slave modes, but in the Guide it will include images of the flash display panels and controls. I hope the information will be helpful here now to users of the Pentax flashes, but also I do hope for any feedback and suggestions about the Optical Slave modes and their use in practice, to help improve the final version for the Guide Supplement ......


THE OPTICAL SLAVE MODES

Optical Wireless Signals
Wireless communication between an on-camera ‘Master/Control’ flash and off-camera ‘slave’ flash/es is achieved within the Pentax Dedicated Flash System (and the other proprietary DSLR systems for that matter) with optical light signals. These signals, which are one-way from the camera hotshoe flash to the slaves (ie there is no two-way communications), comprise of the pre-flashes and the main triggering signals.

The pre-flash is a number of coded instructions containing flash mode information and the signal that tells the slaves to emit their metering test flashes. Once the metering flashes have completed and the camera has calculated the flash exposure needed, then the main triggering signal is emitted, instructing the slaves to fire at a specific power output.

All of these optical signals occur in a very short period of time, measured in microseconds, before the actual flash exposure occurs. There is an additional pre-flash in HS (‘High Speed’) Sync mode due to the need to send exposure time information to the slave/s.


Slave 1 ('SL1') Mode
This is the default slave mode, and applies to all situations where the Dedicated Flash System’s wireless operations are in use. As a general guide this will be for any situation when the on-camera ‘Master/Control’ flash is working in (W)ireless P-TTL mode, and the slave flash/s are set to ‘Wireless’ mode. This is a requirement for standard Wireless P-TTL, 2nd Curtain and High Speed Syncs, as well as when using Manual Flash mode on a slave/s but triggering using the Dedicated Systems Wireless mode.

Slave 1 (‘SL1’) mode enables the slave flash to receive and respond to the coded pre-flash signals from an on-camera flash, so it’s a good item to check if there are issues with triggering the flashes.

It may be easier to look at it from the point of view for when it would not be necessary to use ‘SL1’ mode. This would be for situations when we are not using the Dedicated Flash System’s Wireless operations, so for example when using a third party radio trigger set (either a Manual or ‘P-TTL’ type). In that situation the Optical Slave Mode (‘SL1’ or SL2’) do not matter as it is not actually functional, because the communication is occurring via the third party radio system, not via the Pentax Optical system.

 
Slave 2 (‘SL2’) Mode
There are times when we might want to mix our Pentax system flashes with other non-dedicated types for manual flash exposures, and we may not have radio triggering devices for each flash, or need to use optical triggering for other practical reasons.

Manual flash types do not emit the pre-flashes that the P-TTL models do, but simply fire their set flash output. If a Pentax Slave flash set to ‘SL1’ mode was to detect a single flash pulse from a manual flash, then it would not fire because it would see this single pulse as a pre-flash, and would be waiting for a further triggering signal for the actual flash pulse, which of course would not ever come.

So we can switch to ‘SL2’ mode when using our Pentax flashes as slaves, but triggered by the flash output of another Manual flash. The ‘SL2’ setting changes the way the flash responds to optical signals. Instead of expecting a pre-flash signal with coded instructions, the flash now simply fires its light output immediately and at the same time as any optical signal it receives. So it fires and adds its illumination to that provided by the manual flash that’s actually causing the triggering.

It does not matter if the triggering signal is from an on-camera flash, or another slave flash. So long as the normal ‘line-of sight’ requirements are met between the triggering flash and the slave set to ‘SL2’ mode, it will fire at the same time. So it is possible to create a type of set-up known as ‘daisy-chaining’, where there a multiple slaves optically triggered by the one next to or nearest to them. So an on-camera manual flash could trigger a slave flash, and that first slave flash could then trigger a second slave flash …. And so on and on. With this technique you could solve ‘line-of-sight’ problems between the camera position and a slave, by placing an additional slave flash between the two to ‘pass along’ the triggering signal.

There are different ways to refer to this ‘Slave 2’ type of triggering; it could be ‘Optical Slave’ mode, or I myself quite like ‘Dumb Slave’ mode (because the flash is acting ‘dumb’ by just responding to a simple trigger signal, not the more complicated P-TTL pre-flashes). It is sometimes also referred to as ‘Servo’ mode, perhaps a term used by a different DSLR system.

Please note that when operating in ‘SL2’ optical slave mode, the slave flash must be set to Manual Flash mode, and the power output controlled manually from the flash controls. P-TTL /TTL does not apply to ‘SL2’ mode working. Also, if using another Pentax, or other Dedicated System Flash, as the on-camera triggering flash, then that must also be used in Manual exposure mode. Do not set the on-camera triggering flash to (W)ireless mode either, as that will send out P-TTL Pre-Flashes and cause the slave flash to fire before the actual exposure.
 

Slave Mode Set-Up Steps, AF-540FGZ , AF-360/540FGZII

AF-540FGZ
1) Turn on the Power Switch
2) Firstly, slide the Setting Selector (on the right hand edge of the flash control panel) upwards. This makes the top row of functions available for adjustment
3) Press the ‘Light’ button (left most one of the three) and hold for at least 2 seconds The Slave Mode is displayed, (SL1 or SL2)
4) Press the ‘S’ (Select) button (in the middle of the dial) to change the Slave mode as needed
5) Press the ‘Light’ button once to confirm the new setting

AF-360/540FGZII
1) Turn on the power Switch
2) Press and hold the Function (‘Fn’) button
3) Turn the adjustment Dial to move through the Functions, until ‘SL’ is displayed in the top right of the LCD
4) Press the Setting ‘Set’ button (in between the dial) to cause the numbers ‘1’ or ‘2’ to flash, and rotate the Dial to change the number to the Slave Mode needed
5) Press the Setting ‘Set’ button to confirm the setting
6) Press the ‘Fn’ button to exit the Function Menu

Be aware that in ‘SL2’ Slave Mode, and fairly strong sudden or flickering light source might trigger the flash unexpectedly, so take care if close to it.

(copywrite n mcgregor, september 2016)