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iTTL Protocol


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#1 Alvaro Velloso

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Posted 01 January 2007 - 12:42 PM

Hi all,

Does someone knows where I can get iTTL protocol spacifications ? I'm talking about low level communication between the camera and an external flash unit.

I want to understand how I can get information about ISO, aperture, focus distance etc by the camera bulkhead.

Great 2007 to everybody !

#2 Glasseye Snapper

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Posted 01 January 2007 - 01:26 PM

Hi Alvaro, welcome to wetpixel!

I may be completely wrong here but are you sure all that information gets communicated between strobe and camera? I thought most/all of the calculations were done inside the camera and therefore the strobe doesn't need to know about distance, aperture, etc. the camera just has to communicate the start and stop signals to the strobe and the strobe probably returns some info about its specifications. The Nikon SB-800 description says "The new SB-800 incorporates systems that communicate flash output information during exposures to the image processing ‘engine’ of the new Nikon Digital SLR. " No mention of lots of information being passed from camera to strobe. Again, I'm no expert and others may be able to give you a more authorative answer.

Bart

PS: if you only need the info after the shot is taken then you can simply extract all details from the EXIF header of the image . The exception are the more recent Canon cameras for which the distance information has been blocked out (I recently read a suggestion that Canon dropped distance information from the EXIF header when iTTL was introduced and it may be a patent issue between Canon and Nikon. Just speculation but interesting and annoying for those with Canon cameras.)
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#3 Alvaro Velloso

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Posted 02 January 2007 - 05:34 AM

Hi Bart,

I do appreciate your answer, thanks a lot.
I'm not sure, but probably we can get more information from the camera rather than Trigger/Quench signals.

If there's only Trigger/Quench signals, why do Nikon and Canon use different names to identify their own protocols (eTTL and iTTL) ?

Please check this devices: (go "Converter for iTTL", left menu)
http://www.heinrichs...litz/indexe.htm

I'm myself doing some experiments reading Trigger/Quench times and delivering proper light to an external strobe (basic TTL protocol), but I suppose there's more information I can get from the camera.

Best wishes,
Alvaro

#4 3@5

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Posted 02 January 2007 - 07:42 AM

Hi all,

Does someone knows where I can get iTTL protocol spacifications ? I'm talking about low level communication between the camera and an external flash unit.

I want to understand how I can get information about ISO, aperture, focus distance etc by the camera bulkhead.

Great 2007 to everybody !


i am not sure you will find easily the iTTL protocol specifications. This protocol, as is Canon's eTTL protocol, is a proprietary communication protocol. It is not published anywhere as far as I know.

The makers of converters such as Heinrich Weinkamp or Ikelite or Sea&Sea or of xTTL compatible strobles such as Seacam have spent a lot of time and money reverse engineering the protocol by trapping the comms between each camera and strobe. With the added difficulty that both Canon and Nikon seem to update/change small parts of their xTTL protocols with each new generation of bodies.

I guess to be able to understand iTTL for your camera and strobe you will either have to do the same thing as the people above or maybe ask them to see if they want to share that info with you.

You might also find some sites somewhere on the net where reverse engineered protocols are located but i am sure you would probably have to understand an eastern european or asian language to read them :rolleyes:

Or maybe on some of the nikon related forums you miight be able to find them from someone who has reverse engineered them.

Or you might want to contact Nikon to see if you can licence it ;)

good luck in your searches :D

/paul

Edited by 3@5, 02 January 2007 - 07:42 AM.

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#5 acroporas

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Posted 02 January 2007 - 08:14 AM

I dont know anything about nikon's flashes but at least with canon, there is a lot more communication between camera and flash than just when to fire the strobe.

Canon bodies tell the flash both the focal length of the lens and the crop factor so that the flash can adjust the output angle appropriately. (actual focal length on eTTL flashes and effective focal lentgh on ettl2 flashes) The focal length of the lens currently mounted to the camera is displayed on the lcd on the flash.

ISO, aperature and Shutterspeed are also communicated in some form. It is hard to tell if they are sent as one EXPOSURE signal or if they are all send all three individually. This information is used to calculate the range of the flash. If you change the ISO or aperature, or change the shutter speed when speed is greater than sync speed, the flash knows it and reflects the change by updating range(which is also displyed on the flash's LCD)

Focus distance may or may not be communicated, there is no evidence I can see that says one way or the other as to if the focus distance information is used in the camera or in the flash.

Now figuring out how to get at that information, probably impossible, but if you do figure it out, I bet there would be plenty of thrid party flash manufacturers would be willing to buy that information from you. :rolleyes:

Good luck
William

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#6 Alvaro Velloso

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Posted 04 January 2007 - 05:59 PM

Hi,

Thank you all for helping me.

I'm still searching the web about iTTL protocol. I didn't find it yet, but I found some interesting things I would share with you. Check out what hackers can add to your firmware:

- RGB curves, like Canon 5-D does
- Kelvin temperature
- ISO 100, 6400
- Remote control improvements
- Fast shutter speed
- Color profiles
- Larger Color spaces
- Infrared shots
- Cropping
- Filtering
- Masking

There are also some easter eggs to enable special features (without firmware change).
I found some pay-a-hack groups, sharing a budget for ordering a special feature. They were paying 20$ each.

I'm a D-70 user, and I would be really interested on curves :D

The search goes on....

Edited by Alvaro Velloso, 04 January 2007 - 06:01 PM.


#7 Rattus

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Posted 05 January 2007 - 04:43 AM

Heh, maybe. While some hacks may be easily possible, some of those on the list sound implausible. I'm sure it won't come as a surprise that there are some people who post on the internet who may have a creative approach to the truth.

Many "Camera Firmware Specialists" may turn out to be lying little toerags just looking for net-kudos for their fantasy personality. Hey, who isn't? :D

Martyn
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#8 Alvaro Velloso

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Posted 03 April 2013 - 06:10 PM

Hi all,

 

I finally found what I was looking for. Not need to hack it anymore.

The protocol is a little bit more complex than I expected, but still feasible to implement.

 

http://cms.diodenrin...10-ittlanalysis

http://off-the-clock...-flash-analysis

 

I'm developing a strobe with special features and this protocol may be a good adition in the future.

 

All the best, Alvaro