S120 + YS-01 - Erratic TTL

[Interceptor121]

The fibre optic connection is most likely irrelevant
Is the camera itself flash control mechanism
If you fire your camera out of the housing at distance it will give a full blast because it is aware of the weakness of the internal flash. Basically it works as per design there is little light you get a full blast

 

[007wilk]

OK, then why do I get the TTL failure signal, as evidenced by the LED light sequence? This must be something in the strobe... It probably means that the amount of light (or is it digital signal?) received via fiberoptic cable falls outside a range that is acceptable to the strobe to perform TTL.
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An Update:
Another complication... I have just put a wide angle lens on the housing. With the WA on, it appears that the TTL does not even work with any level of reliablity for objects located beyond 2 ft... I can easily imagine myself shooting a fish from such a distance...

 

[Interceptor121]

The strobe does not perform any TTL the camera does. The camera sends a start and stop signal to the strobe. If the strobe does not get a stop signal because the camera does not detect a return in the sensor it stays red and does no go through green, in that case the strobe fires at full power.
You can download the pictures to a program and check the Exif, if you see strobe return NOT DETECTED means the camera TTL failed. You can have some fun and take a not of your shots when you get or not the green and then you will see you get green when return is detected and red when is not
The strobe only fires at the same power what changes is the time which is controlled by the camera TTL.

Not sure about your last comment, obviously you need the lens and the strobe and keep aiming the strobe at the subject so that the light bounces back in the camera lens

 

[007wilk]

Interesting.. I did not know the flash information was being recorded with the image file...
Unfortunately, I used a few different Exif viewers / editors and could not find "strobe return" or anything similar anywhere... Do I need a special exif reader that can see it? There are a few flash variables, as shown below:

Good pic:
Flash output = 49
Flash guide number = 2.59
Flash activity = not set
Flash details = E-TTL, built-in


No TTL pic:
Flash output = 500
Flash guide number = 4.75
Flash activity = not set
Flash details = E-TTL, built-in

So, definitely the flash output for the failed picture is high… Not sure if it is at a max, or not…
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Let me re-phrase the wide angle comment. What I meant is that with the wide angle lens on, the TTL only works at distance of some 2 ft, or less. Beyond that, no TTL and everything is overexposed. And I am aiming the strobe correctly.

 

[Interceptor121]

The wide angle lens in air moves the focus point of the camera further away so the camera thinks the subject is far so shoots a full dump. I think canon on board flash is less than gn5 so anything the camera thinks is out of reach will generate a full dump. Use canon photo professional to see mode details
More than anything why would you shoot TTL something further away then few inches?
Backscatter would be guaranteed aiming directly at the subject

---------- Post added March 11th, 2014 at 08:18 PM ----------

Just for fun I set up my rig (Sony rx100 and two inon z240) and started shooting with a fisheye lens and strobes directly on front not even pointing at the subject. With subjects at 5 feet away I get regularly ttl return and green light.
Having had an YS-01 I can only guess that the pre-flash of the strobe is not strong enough to be detected by the camera. When I still had the YS-01 I tried it together with the inon and the pre-flash of the inon was so strong the YS-01 shot at the minimum when instead i had it on its own it worked fine. I think the TTL implementation of sea and sea is just limited and as you suggest seems to work only at short range