Slave TTL for Digicams

Slave TTL for digicams: D2000 vs. DA2 + Z220

Slave TTL for compact digital cameras

There are several solutions around to drive an external strobe with your compact digicam. Especially optical slave TTL has proven to offer decent full automatic strobe power control as it is based on the camera's own TTL metering system.

The basic method is quiet simple. The camera's internal strobe is the trigger (mother) strobe. When it starts to emit light the external strobe is fired accordingly. As soon as the camera's internal strobe has extinguished the external strobe will be shut down as well. This way every flash is copied 1 by 1 to the external strobe in terms of lightning duration.

As the internal strobe is driven by the camera's TTL metering system you have the same exposure result with the external strobe.

This kind of slave TTL has its limitation if you intend to use big amphibic strobes (big ring type tubes for example) which require a long time to burn down when dumping full power. The camera's internal strobes simply burn down to fast and are already extinguished before the big external strobe can dump its full power.

Digital Adapter 2 (DA2)

The Digital Adapter from Matthias Heinrichs has been the first popular slave TTL solution for compact digicams. As most midrange amphibic strobes burn down very quickly (for example Z220 and YS-60) the full power limitation for big strobes was no item to consider in real underwater life.

Nevertheless the new Digital Adapter 2 has addressed this drawback with the opportunity to adjust a certain gain factor for extending the lightning duration. An example with completely virtual numbers:

factor 1.0 (no gain):

internal preflash: 100µs external preflash: 100 µs
internal mainflash: 200µs external mainflash: 200µs

factor 2.0 for the external flashes

internal preflash: 100µs external preflash: 200µs
internal mainflash: 100µs external mainflash: 200µs

factor 3.0 for the external flashes

internal preflash: 100µs external preflash: 300µs
internal mainflash: 66µs external mainflash: 200µs

The resulting external mainflash has always the same length. Just the preflash (internal and external) and the internal mainflash are influenced by the gain factor. The DA2 comes with factory default setting of 1.0 (no gain). Adjusting a higher gain factor allows slow and huge amphibic strobes to dump full power in TTL mode. Additional nice side effects:

Another nice DA2 feature is the µrecorded TTLµ mode in order to avoid optical feedback. It works this way: First record the internal flash and wait until it has been extinguished. Thereafter trigger the external strobe. You donµt have to be to critical about light blocking mounting options anymore as feedback effects are suppressed.

Inon D-2000

In the past Inon has (like others) offered external auto strobe options (D-180 series) for digital compact cameras. The drawbacks of such systems are well known: independent metering system does not know what aperture and sensitivity (ISO) is set on the camera and has to be entered manually into the strobe. The point of view and angle of view is always different (camera lens vs. strobe auto sensor). Meanwhile the D-2000 is released and Inon joins the slave TTL club as well.

Basically the D-2000 is a slave TTL strobe except that it does not feature a consistent 1 by 1 copy of the camera's internal strobe. Unfortunately Inon would not provide information on how µS-TTLµ really operates.

Based on some measurements the following is suspected: there is a consistent extension/gain on the lightning duration in relation to the camera's internal strobe. For example: S-TTL-low, preflash, camera internal strobe 50µs, D-2000 215µs.

This seems to be quiet convincing for another reason: +/- compensation dial on the D-2000's back.

Without the extension/gain the internal and D-2000's mainflash would have the same lightning duration. The D-2000 does not know when the camera's internal strobe will be turned off. Therefore it would not be possible to shorten the D-2000's mainflash in relation to the camera's internal mainflash.

If the D-2000's lightning duration is always gained (as suspected above and roughly similar to the DA2) there is an opportunity to assign a minus compensation to the mainflash by shortening the lightning duration.

Another possibility to enable +/- compensation is to assign a compensation influence to the preflash and manipulate the camera's TTL metering system.

Test - Setup

Canon S60 (internal strobe blocked), exposure time 1/60 s, distance ~30cm.


focus light + laser: on

focus light + laser: off

D2000,S-TTL low
focus light: on
(without red filter*)

D2000,S-TTL low
focus light: off

f 3.5

f 4.0

f 4.5

f 5.0

f 5.6

f 6.3

f 7.1

f 8.0

*I had expected the D-2000's focus light to turn off automatically during pre- and main flash in order to avoid any influence on the TTL exposure metering system (like DA2+Z220). According Inon this is just the case when the main flash fires. Inon recommends using a red filter in front of the focus light. It seems that the filter is not just a compensation tool for whitebalance as advertised, but necessary for correct TTL exposure results in critical situations (for example: night dive macro work).

Todayµs matrix TTL systems work very reliable and with slave TTL you can use it in conjunction with an external amphibic strobe.
The Inon D-2000 incorporates the optical slave TTL function featuring +/- compensation dial for comfortable access underwater.
In addition you have quick access to manual strobe power settings on the D-2000. In manual mode it avoids to dump the full power upon preflash receipt as the D-180 before has done. For manual power settings in combination with the DA2 you have to select a camera mode featuring a mainflash only (no preflash, for example Canon S60: µMµ). Otherwise two flashes are fired µ each with the intensity according to the manual power setting. If more than µ power is selected there is not enough juice left for the mainflash.

Nevertheless the D-2000's modelling light system is a design flaw in my opinion as it is not suppressed during the preflash. This affects the TTL metering and leads to incorrect results as long as the recommended modelling light filter is not used (The modelling light system seems to be quiet identical to the D-180µs one. Difference: an auto strobe does not care about modelling light influence during preflash, but the TTL metering system does which drives the D-2000)

Which one to choose? The D-2000 offers good and simple handling and provides the advantage of slave TTL. If you donµt have an upgrade in mind (DSLR, etc. which require a sync cord connection) you get a nice all-in-one unit. Especially the +/- compensation dial makes a lot of sense when using small compact digicams which have limited and/or complicated flash exposure control access.

On the other hand you have the DA2 featuring superb slave TTL operation, recorded TTL mode to avoid optical feedback and user settable gain factor. It is compatible with many amphibic strobes (pick a strobe of your choice which fits your needs). It even fully supports the Inon Z220µs modelling light and laser (including suppression during pre- and mainflash!). It comes for less money than a sync cord and you might already have a strobe which just needs a DA2 in order to offer slave TTL with your digicam.

As a Nikonos V & SLR shooter I naturally would not invest my money into a strobe without sync cord connection. And I prefer to use my modelling light without filters for close up work as well. Iµve added a DA2 to my existing gear and now have a nice handy backup rig to my SLR gear.

+ easy mounting options if your camera/housing is supported
+ quick and comfortable +/- TTL compensation
+ manual power settings unrestricted and quickly available
- odd modelling light system design. Filters required for compensating TTL metering manipulation during preflash
- no sync cord connection for future upgrade
- no proper mounting solution available if your camera/housing is not supported
- Was shipped with a Japanese manual only

+ works with many strobes (your choice!)
+ µrecorded TTLµ to prevent optical feedback
+ user settable gain factor
+ standard sync cord connection for future compatible strobes
+ supports Z220µs modelling light and laser light. Including suppression during pre- and mainflash
+ price (less than a sync cord)
+ support with English/German instructions and detailed information on how the product works
- as a slave adapter it can not feature +/- compensation as the D-2000 does
- manual power settings limited with certain cameras in certain modes
- mounting might be up to you

DA2 mounting example

blocks internal strobe and mounts DA2
(not recommended if there is force on the sync cord)
Provided by www.mike-dive.de

2005 Julian Scheunemann

Note that INON Japan has provided an official response to Julian's article.