[MrclSchprs]

Hello,

Does anybody know if Pentax made some changes in their flash protocol? I am trying to figure out if the AF assist feature of the Cactus V6 II trigger will work on my aging 645N film camera. According to Cactus the AF assist feature works with the recent digital K camera's as well as the 645Z and 645D. So, if the communication between camera and flash did not change, it should work on my film AF film 645 as well.

Any thoughts on this?

Marcel

[08amczb]

It won't work, the 645, 645N and 645NII does not support P-TTL, only the plain old TTL protocol.

[MrclSchprs]

Yes, that I know. But I do not have any interest in TTL mode, I am only interested to use the AF assist spot beam

[08amczb]

The protocol also changed, I would be supprised if it works, but I don't have any flash with AF assist light apart from the 540FGZII which does not work on my PZ-1p and only has a led video light. (The led light on the PZ-1p does not work as af assist, it works on the KP and on the K-30.)

[rawr]

There are a lot of patents that cover Pentax flash protocols - like this one:

US6718135B2 - Flash photography system - Google Patents

But there is no easy way to get a complete list of everything in the Pentax flash protocols, and what may have changed over the years, other than trawling through this and other Ricoh or Pentax patents lodged over the years.

[mcgregni]

The comunications between the V6II and camera uses the more recent digital P-TTL protocol, that is how we understand it. So in theory the functioning of the AF assist on the V6II and any slave flashes would depend on support for P-TTL ..... So in theory you should not expect AF assist to work with a V6II and a 645N camera.

But you may be the one to prove the theory wrong!

[MrclSchprs]

It's confusing!

The Pentax MZ-S manual states that the AF spot beam works with the older - at the time - AF 500FTZ and AF 330FTZ flashes as well as the - again at the time - new AF 360FGZ flash. I own a 330FTZ flash and tested it on my MZ-S as well as on my 645N body. And the AF spot beam works on both camera's.

The 645N camera predates the MS-Z camera. So the 645N manual does not say anything about the 360FGZ or 540FGZ flashes, but it claims that the AF illuminator works on the older flashes and it does as it works with the 330 flash.

So, using some simple logic I was hoping to derive compatibility. If an older flash works on the 645N and that same flash works on a newer camera that is also compatible with a newer flash that according to Cactus is compatible with their trigger the 645N should - in theory - work with the trigger as well.

My best option is to find someone not too far from where I live that owns a Cactus compatible flash, drive over and mount the flash on my 645N to see if the AF beam lights up and if it does the Cactus trigger should also work.

BTW the reason that I specifically looking at that Cactus trigger is that it allows me to use the AF spot beam _AND_ trigger my studio heads using the Elinchrom Skyport trigger mounted on the cactus trigger. Does that make sense?

[CarlJF]

It's confusing!

The Pentax MZ-S manual states that the AF spot beam works with the older - at the time - AF 500FTZ and AF 330FTZ flashes as well as the - again at the time - new AF 360FGZ flash. I own a 330FTZ flash and tested it on my MZ-S as well as on my 645N body. And the AF spot beam works on both camera's.

The 645N camera predates the MS-Z camera. So the 645N manual does not say anything about the 360FGZ or 540FGZ flashes, but it claims that the AF illuminator works on the older flashes and it does as it works with the 330 flash.

So, using some simple logic I was hoping to derive compatibility. If an older flash works on the 645N and that same flash works on a newer camera that is also compatible with a newer flash that according to Cactus is compatible with their trigger the 645N should - in theory - work with the trigger as well.

The MZ-S supported both the legacy TTL and, at the time, newer P-TTL modes. The 360FGZ and 540FGZ also supported both modes. So, it's expected for the MZ-S to work with the older flahses (the camera will simply work in legacy TTL mode) or for the 360FGZ and 540FGZ to work with older camera as the flashes will set themeselves in legacy P-TTL mode.

Now, the Cactus only support P-TTL. So, if you put it between the camera and the flash, both have to support P-TTL to work. If one or both of them doesn't support P-TTL, the cactus should not be able to pass the data between the devices. Or, at least, it's not a supported mode of operation, AFAWK. It still could work, but not expected to, and thus don't be surprised if it doesn't.

[howieb101]

You can force the AF assist light to always on with the V6 II. Message me and I'll send you the instructions.

[stevebrot]

The comunications between the V6II and camera uses the more recent digital P-TTL protocol, that is how we understand it. So in theory the functioning of the AF assist on the V6II and any slave flashes would depend on support for P-TTL ..... So in theory you should not expect AF assist to work with a V6II and a 645N camera.

The 645N has the "data" contact on the hot shoe and supports both the digital and legacy analog TTL and dedication protocols meaning that it has wide (full?) compatibility (within limits of body features) with all Pentax flashes with the exclusion of the current model AF360FGZII/AF540FGZII. The most recent flash models reflect a change in the digital dedication protocols related to the AF assist feature. While the 645N supports AF assist under the previous dedication protocols, it will not with with the two newer flashes.

The question is whether Cactus emulates AF assist dedication and (if so) which digital dedication protocol (newest or previous) it supports, if any. Statements on this thread indicate that support is offered and that it is backward compatible. It should work.

Note: I forgot to mention that AF spotbeam support is independent of TTL/P-TTL on the 645N and several other models.


Steve

(...not an expert in this stuff except for having some knowledge of legacy flash dedication and body support...)

[mcgregni]

Just considering this is in a practical real world way .... I doubt that AF assist beams from flashes combined with the 645N with medium format lenses is going to offer a good autofocussing experience .....?

Assuming you're working with static subjects in a studio, perhaps a strobe with a modelling light to allow you to manual focus might offer more accuracy and reliability....

[RKKS08]

The MZ-S supported both the legacy TTL and, at the time, newer P-TTL modes. The 360FGZ and 540FGZ also supported both modes. So, it's expected for the MZ-S to work with the older flahses (the camera will simply work in legacy TTL mode) or for the 360FGZ and 540FGZ to work with older camera as the flashes will set themeselves in legacy P-TTL mode.

The *istDS supports TTL as well as pTTL
BUT !!
If the flash also supports both modes, the camera cannot be forced to use TTL.
Unfortunately, this is also true if the flash can be set manually to use either TTL or pTTL, as it seems the camera can detect (at least with Metz flashes) that the flash is capable of pTTL. Then the camera will not send the signal to stop the flash, and the flash will ignore the commands for pTTL from the camera. The result is chaotic behaviour.

Change of protocol by Pentax:
There have been several. I own 2 flashes (1 Soligor, 1 Cullmann), which work alright (pTTL) with the *istDS and the K200D, but turn into a stroboscope with the K-5 (and set the top display illumination blinking).

[MrclSchprs]

I've found someone who is willing to let me let me use his AF540FGZ so I can do a test. Tomorrow or the day after tomorrow I will report my findings.

[mcgregni]

Great! Our reputations for accurate assumptions, theories and making it all up are at stake!

[stevebrot]

Great! Our reputations for accurate assumptions, theories and making it all up are at stake!

Run! Run! Run!




Steve