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11-06-2018, 01:54 PM   #166
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QuoteOriginally posted by Class A Quote

Correct, it isn't.

The quench signal was used for analog TTL. The moment the camera sensed that enough light has fallen on the sensor, it activated the quench pin, thus causing the flash to immediately stop creating output. As inkista wrote, the length of the output determines the power of the output (for IGBT-controlled flashes, i.e., all speedlights)....
Yes, the IGBT does the actual quenching and an IGBT is a digital circuit. But I'm not convinced that the IGBT control signal has to be a new digital signal vs. the older analog quench signal, since IGBTs are still voltage controlled. Simply inverting the old-style quench signal might work to turn the IGBT on/off, assuming the old quench signal was low to high, not high to low. The timing would be the same for the same power levels. Nikon and Canon both have flashes that can switch between older-style film/reflectance TTL and newer-style preflash digital TTL. And both the hotshoe pinouts indicate quench signals are still there. Just makes more sense to me to use the existing signal that does the same function.

But then, I'm not a flash engineer.

11-06-2018, 02:10 PM   #167
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Thinking more about it, the camera could not determine the actual duration, because this would not allow for different GN flashes. The camera must calculate an EV figure which is converted to a suitable duration by each individual flash.
11-06-2018, 02:31 PM   #168
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QuoteOriginally posted by inkista Quote
This is good to hear! I'd suspected as much from the TT600's ability to do HSS. I'm assuming the only thing that won't work without a specific Pentax firmware update for the TT685 flashes is TTL. HSS and remote power control are probably fine.

Out of curiosity, what does it say on the LCD of the TT685-C to indicate it's in Pentax mode?
Well, the XPro-P says ETTL and the flash says ETTL, and my exposures seem decent.

Not sure what you mean by saying it's in "Pentax mode". These flashes don't say which camera brand mode they are in - there is no "indicator" on the LCD. Perhaps some of the other Godox models do.
11-06-2018, 02:59 PM   #169
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QuoteOriginally posted by mcgregni Quote
There has to be a calculation of duration, but inkista, you seem to be suggesting that this is carried out by the camera and communicated at the point output ceases..... But P-TTL output is all pre-determined during the pre-flash stage, so it seems more likely to me that a coded data message is sent from the camera containing the "output instruction" ...(is this a time value or something else that is converted to a duration inside the flash?)..
I agree. It has been my understanding that the camera passes meter readings along with exposure settings and perhaps a time sync. The magic is in the flash and the camera need not know the flash's capabilities or configuration. I have often wondered if it is the flash that actually triggers the shutter rather than the other way around. (Just kidding)


Steve

11-06-2018, 03:24 PM   #170
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QuoteOriginally posted by ProfessorBuzz Quote
Well, the XPro-P says ETTL and the flash says ETTL, and my exposures seem decent.
Cool. That's unexpected, though. Usually TTL function is what you're waiting on the firmware release for.

QuoteQuote:
Not sure what you mean by saying it's in "Pentax mode". These flashes don't say which camera brand mode they are in - there is no "indicator" on the LCD. Perhaps some of the other Godox models do.
It's in the lower-left corner, and it's easily missed. It may also require switching in the same session before you see it. Not 100% sure. But here's my TT685C's LCD when used in quick succession with my XPro-C, XPro-F, and XPro-O:

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My TT685C is also at firmware v3.3. I was just curious what it said if you used it with an XPro-P. I think the other two systems say Nikon and SONY, but don't quote me on that.
---------- Post added 11-06-18 at 02:34 PM ----------

QuoteOriginally posted by mcgregni Quote
Thinking more about it, the camera could not determine the actual duration, because this would not allow for different GN flashes.

The camera must calculate an EV figure which is converted to a suitable duration by each individual flash.
But isn't that what the pre-flash metering/reflectance takes care of? A more powerful flash's pre-flash/reflectance would be brighter, and either meter that way or bias towards an earlier cutoff.

Last edited by inkista; 11-06-2018 at 03:36 PM.
11-06-2018, 03:53 PM   #171
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QuoteOriginally posted by inkista Quote
But isn't that what the pre-flash metering/reflectance takes care of? A more powerful flash's pre-flash/reflectance would be brighter, and either meter that way or bias towards an earlier cutoff.
The pre-flash power depends on a distance estimate provided by all Pentax AF lenses and is about the same at close and moderate distance regardless of flash specification. If the pre-flash cannot be adequately quenched close-up, P-TTL essentially fails presumably due to the meter reading being outside linear range. This sometimes happens with vintage manual focus lenses where the distance information is not available. With those lenses, the pre-flash is done at fixed power and fails badly at close distance and wide apertures.

It might help to know that the pre-flash happens with the mirror down using the regular light meter.


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11-06-2018, 05:58 PM   #172
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QuoteOriginally posted by stevebrot Quote
The pre-flash power depends on a distance estimate provided by all Pentax AF lenses and is about the same at close and moderate distance regardless of flash specification. If the pre-flash cannot be adequately quenched close-up, P-TTL essentially fails presumably due to the meter reading being outside linear range. This sometimes happens with vintage manual focus lenses where the distance information is not available. With those lenses, the pre-flash is done at fixed power and fails badly at close distance and wide apertures....
That's interesting. I'd never heard the power level of the preflash varies. I always read the distance information was used to refine the power adjustment of the main burst. The value of the preflash is that it's a given/known power level. Wow. P-TTL is really different from eTTL-II.

---------- Post added 11-06-18 at 05:25 PM ----------

Whoops missed this.

QuoteOriginally posted by mcgregni Quote
My assumption was that the term "quench signal" was referring to camera to flash communication (for film plane TTL), and flash light sensor to flash (internally) for thyristor types.
Ah. No. There are actual pins/contacts that give a quench signal for Canon and Nikon hotshoes/flashes and they're used for TTL.

Thyristor modes for a Canikon shooter aren't related to TTL. The thyristor itself performs the quenching, so there's no need to signal a quench. That's why autothyristors can work independently of a camera. "A" modes on Nikon (and the Ext. modes for Canon) don't require any flash/camera communication at all to set the flash's power.

QuoteQuote:
How digital P-TTL flashes technically turn their output on and off internally is beyond my electronics knowledge, but also surely beyond what an operator and controller of flash exposures needs to know ...?
Yes, but we're talking about reverse-engineering the signal. Not just using it. If you're reverse-engineering, like Godox, then you do need to know.

QuoteQuote:
There has to be a calculation of duration, but inkista, you seem to be suggesting that this is carried out by the camera and communicated at the point output ceases.....
I can see how you can interpret that, but actually what I'm thinking the digital TTL model is, is that the camera tells the flash to send out the preflash at a known power level/duration. Then meters the preflash, and based on the level reported back from the metering, makes the flash power adjustment, and tells the flash to use that power level via the sync and quench signals. Similarly, in M mode, the camera can be used to set the M power level (via camera menus) and control that power level via the sync and quench signals.

QuoteQuote:
But P-TTL output is all pre-determined during the pre-flash stage, so it seems more likely to me that a coded data message is sent from the camera containing the "output instruction" ...(is this a time value or something else that is converted to a duration inside the flash?). ...
But to me, there are only four pins on the Pentax hotshoe. One of which is already dedicated to the sync mode, and the other three still have to backwards-compatible for film camera usage. So the new flash communication protocol must be, at least partially, compatible with the older analog signalling, or at the very least, cannot disrupt it if it's in use. And, decoding a digital signal is going to be a lot harder than decoding an analog one. It's easy to read voltage/amperage on a signal. Harder to decode what values 001, 010, and 100 could possibly mean.

QuoteQuote:
But in any case, it seems to me that exactly how a digital TTL flash technically achieves the right duration has little significance to practical P-TTL flash operation.
But a huge amount on reverse-engineering, given the visibility into a given signal if it's done one way or the other.

QuoteQuote:
The coded message could be something like this ...(English translation) .."Turn on ...wait 1/10,000th sec ....Turn off". But I am thinking this is all carried out by the internal electronics of the flash, and not through hotshoe contacts (apart from the data transmission at the end of the pre-flash stage).
But that "after the preflash-stage" external signalling between the flash and the camera is all that a 3rd-party engineer has to hook functionality onto for their own gear. As far as they know, whatever happens internally is a black box. They can only mess with the signals coming into and going out of that box. I.e., you can only put a voltmeter onto a flash foot pin or a camera hotshoe contact.

Last edited by inkista; 11-06-2018 at 06:25 PM.
11-07-2018, 08:14 AM   #173
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QuoteOriginally posted by inkista Quote
It's in the lower-left corner, and it's easily missed. It may also require switching in the same session before you see it. Not 100% sure. But here's my TT685C's LCD when used in quick succession with my XPro-C, XPro-F, and XPro-O:
My TT685C is also at firmware v3.3. I was just curious what it said if you used it with an XPro-P. I think the other two systems say Nikon and SONY, but don't quote me on that.
Ok, when I test fire it (lightning bolt) with the XPro-C, it says Canon; wih the XPro-P, nothing there. I had never noticed this before - thanks for pointing it out.

So perhaps there will be a firmware upgrade in future.

11-07-2018, 10:50 AM   #174
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QuoteOriginally posted by mcgregni Quote
But P-TTL output is all pre-determined during the pre-flash stage, so it seems more likely to me that a coded data message is sent from the camera containing the "output instruction"...
Yes, that's right.

I'd bet my bottom dollar that the analogue legacy pins hardly play any role in the P-TTL protocol. It's all done through digital codes.

As far as re-engineering effort is concerned,
  1. several companies reverse-engineered P-TTL, suggesting it is a manageable task. I don't want to trivialise it, but the empirical evidence suggests that it is doable, even when the returns won't be as massive as they are for Canon, etc.
  2. I could imagine that some companies didn't have to start from scratch but sourced some reverse-engineering groundwork, or even the fully monty from a third-party. Why wouldn't this kind of knowledge be for sale? Alternatively, sometimes company secrets leak through employees.
11-07-2018, 11:14 AM   #175
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Inkista seems to be claiming that the only knowledge needed is the electrical signals detectable from the hotshoe contacts ....

It seems likely, considering the points raised here, that the flash model profiles used by the Cactus V6II are primarily to take account of the different Guide Numbers of each flash. Because the "output instruction" from the camera must be translated by the V6II Tx unit into an on-duration-off message for the flash.

Bearing this in mind, surely all TTL Radio Trigger designers need to understand the format, the "Protocol", of how the camera digitally describes the required flash EV....?

Last edited by mcgregni; 11-07-2018 at 11:25 AM.
11-07-2018, 07:06 PM   #176
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QuoteOriginally posted by mcgregni Quote
Inkista seems to be claiming that the only knowledge needed is the electrical signals detectable from the hotshoe contacts ....
That may be and some manufacturers may provide tighter body-flash integration by doing so. However, that is not how our current cameras work.

Many of the participants on this thread benefit from working with a variety of vintage flash and cameras and also from the shared knowledge on this site and the very valuable "K-mount Page"* and other online references. The key phrase here is "backward compatibility", or lack thereof, regarding the hot shoe and how features are supported as well as the key difference between flash exposure control protocols and flash dedication.** The previous generation of AFnnnFGZ flash (no "II") offered compatibility of both features and dedication back to the M-series bodies of the late 1970s. The current generation does not, a tradition that goes back to the addition of the data contact with the AF bodies. Of the three TTL protocols used since then (analog TTL, digital TTL, and P-TTL), all three were in use by various film bodies when P-TTL support was added in 2001 hence the inclusion of all three on the flagship AF360FGZ in that year.

The K-Mount Page | Information about Pentax technology

Why is all this pertinent? Only because flash support for analog TTL was rather rare in the line once the data contact became standard on the AF bodies; most flash models required the data contact for exposure control with only a few being compatible with the analog TTL LX model camera. While it is theoretically possible to quench discharge using the analog contacts***, it has been several decades since such as been done with new product cameras.

Does that mean that the two analog contacts are "extra baggage" on current model cameras and flash? No, not at all. They are apparently still leveraged for mundane dedication tasks and even provide for limited backward compatibility with legacy flash. For example, my 1980-vintage AF280T, an analog TTL model, will signal my K-3 to properly set aperture for so-called "program flash" with auto-thyristor flash control and several other features. Go figure.

Going back on-topic, that data contact is where the handshake happens to allow the attached flash to control the P-TTL show for itself and optical slaves with fairly mundane input from the body.


Steve

* The KMP has a decent explanation of Pentax hot shoe and flash dedication and how analog TTL works. The explanations for digital features is quite weak and/or misleading, however. (LINK)

** Flash dedication is the set of features that allow the flash to use available camera support and for the flash to offer the same back. In simplest form this may be limited to signalling flash ready to allow a viewfinder signal and setting of shutter to sync speed. On more capable bodies and flash, dedication may extend to negotiating appropriate lens aperture and such based on the flash mode. It is related to, but not the same as flash exposure automation. Flash dedication uses the "analog" contacts ("mode" and "ready") and may also use the data contact for some features.

*** The quench function of the analog TTL protocol is handled through the "mode" contact, which is held "low" until sufficient light has been detected by the body.

Last edited by stevebrot; 11-07-2018 at 07:18 PM.
11-07-2018, 07:28 PM   #177
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No news about v860 II for pttl?
11-14-2018, 12:04 PM   #178
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For the XPRO TRIGGER (sony/fuji/panasonic) , there is, today, 3 news firmware updates on godox download page
12-03-2018, 10:09 PM   #179
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I shoot interiors using a K3. I just purchased the AD200 w/ XPro-P trigger. I shoot using a one light technique meaning I take multiple frames of one scene and in post production I stack/layer-mask/brush-in desired parts of those multiple images. Anyway, to the problem Iíve run into.

I always begin shooting each scene using the K3, 5 stop bracketing feature in (Av)Aperture priority in order to achieve a base ambient frame. However, if the XPro is switched on, the bracketing feature doesnít work. It simply shoots the 5 exposures at the very exposure to which the camera is initially set. Iíve tried bracketing in other modes but with the same outcome.
I was using a Phottix trigger w/ Yongnuo flashes and did not have this problem. Also, I only shoot with flash in manual mode.
Any advice?
6 Days Ago   #180
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QuoteOriginally posted by ckeene Quote
I shoot interiors using a K3. I just purchased the AD200 w/ XPro-P trigger. I shoot using a one light technique meaning I take multiple frames of one scene and in post production I stack/layer-mask/brush-in desired parts of those multiple images. Anyway, to the problem Iíve run into.

I always begin shooting each scene using the K3, 5 stop bracketing feature in (Av)Aperture priority in order to achieve a base ambient frame. However, if the XPro is switched on, the bracketing feature doesnít work. It simply shoots the 5 exposures at the very exposure to which the camera is initially set. Iíve tried bracketing in other modes but with the same outcome.
I was using a Phottix trigger w/ Yongnuo flashes and did not have this problem. Also, I only shoot with flash in manual mode.
Any advice?
I just tried this with the XProP on my K-3, controlling the TT350P. 3-step bracketing worked fine (once I waited for the flash to recycle before the next shot) in both P mode and Av mode. I also tried it with the TT350P on camera and it also worked fine.

The only thing I can think of to explain your issue is this. Say you set the aperture to f5.6 and the ISO to 400 (fixed not floating). To get the variation in the bracketed exposures the camera would need to adjust the shutter speed. Would it be unable to bracket properly if each shot were bumping against the maximum sync speed (1/180th or 1/160th depending on the EV steps setting)? Seems a long bow, but that's all I can think of.

Try bracketing in another camera mode (e.g P)?
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