S120 + YS-01 - Erratic TTL

[007wilk]

It sometimes works and sometimes it does not... I see no pattern at all.. It happens in all camera modes: A, P, Av and Tv. When it does not work, the shots are typically totally over-exposed, but depending on the mode and light conditions, they may also be almost totally dark.

There is a LED sequence on the strobe which is supposed to switch the LED color from red to green for a moment after the shot, if everything goes well.
For the pictures that come out OK, it happens as described above. For all the bad pictures (under or over exposed) the light goes off for a few seconds and comes back red, i.e. never switches to green.

My Settings:

The YS-01 is set to TTL and max power.
The camera flash settings:

Flash mode = Auto
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Flash Exposure compensation = 0
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Shuter Sync = 1-st curtain
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red-eye settings = off
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SafetyFE = off
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I have re-installed the f/o cable, checked it as best as I can and see nothing wrong with it... Using a fiber optic kit supplied by Fantasea with two plugs to which I had to attach the cable. Any know issues with this item?

The camera is in an Ikelite housing. I used electrical tape on the inside of the housing to mask the internal flash. The fiber-optic cable socket on the housing is not directly facing the flash but instead is positioned above it just slightly in front of the flash. Could that matter? Can the use of non-reflective el. tape on the inside of the be causing insufficient light reflection? Not sure how "picky" the f/o cable is...

 

[Interceptor121]

for TTL to work you need to aim the strobe directly at the subject otherwise it will not detect a return. If return is not detected TTL thinks there is not enough light and the strobe fires a full blast overexposing the picture

 

[007wilk]

Thx for the suggestion. I will investigate it later tonight, but in general, I thought I was aiming the strobe more or less towards the subject...

 

[Interceptor121]

Switch the aiming light on so you know you are pointing direct

 

[007wilk]

I do not think this is it...

But I did notice the TTL fails almost every time when I aim the strobe towards a dark distant wall... When aimed at close and/or bright objects it seems to work much more consistently... It could be insufficient feedback suggesting the need for full blast. I understand that for a distant object I may want the flash to fire at full blast but right now the TTL fails sometimes as close as in the 6-8+ ft range, which I would say is way too close... We will see what happens under water but right now I don't like the way it works at all...

 

[Deep Water Dan]

I'm thinking you may have more than one issue at work here. First of all, the mode switch has four settings including "off". Make sure you consistently select the correct one, two of them are pretty close together. As far as your dark pictures go, I would bet that you aren't allowing enough time for the strobe(s) to recycle. One reason this can happen is low batteries. Low batteries can work fine on close shots, but as soon as you shoot something far away it can take 30 seconds or so for low batteries to recharge the strobes. Even with fresh batteries, if you shoot something far enough away the strobes can take quite a while to recycle. The camera will let you shoot, but the strobes won't fire. This would be consistent with your statement that you don't get a "green" indication. You shot, got a good picture and a green light, took the next shot before the strobes recycled, and got a dark one with no green light. Then you got a red light. The long shot is a bad fiber optic cable. It happens, I just had to replace one of mine. Could be that sometimes it works and other times it doesn't. And if it's intermittent it could cause either overexposed or underexposed shots depending on the exact moment it decided not to work.

Let us know how this turns out.

Dan

 

[Interceptor121]

I do not think this is it...

But I did notice the TTL fails almost every time when I aim the strobe towards a dark distant wall... When aimed at close and/or bright objects it seems to work much more consistently... It could be insufficient feedback suggesting the need for full blast. I understand that for a distant object I may want the flash to fire at full blast but right now the TTL fails sometimes as close as in the 6-8+ ft range, which I would say is way too close... We will see what happens under water but right now I don't like the way it works at all...

The strobe is a GN 16 in air. So at 8 feet which is 2.4 meters you can only shoot around f/5.6 and not a completely dark wall anyway.
In water really you can cover at most 3 feet ideally you want to shoot at 1 foot or less further away is just back scatter

 

[007wilk]

Yes, but still... I see no reason for the TTL to be stopping to work so abruptly...
How does your setup work above water? Would you be seeing the same behavior? I am guessing not...

 

[Interceptor121]

Yes, but still... I see no reason for the TTL to be stopping to work so abruptly...
How does your setup work above water? Would you be seeing the same behavior? I am guessing not...

I use TTL only for macro hence, if I point in the distance straight I go manual. TTL is only good if you aim direct and you only do that with small close stuff. I do not see the point of doing tests of situations that do not apply to my shooting style

 

[007wilk]

I see your point Interceptor.. Yet, it still bothers me, if something is not 100% repeatable And it also bothers me that the TTL failure is so sudden. It either works reasonably well or does not work at all. Almost as, if there were some sort of a set point defined, which says if you get less than X of the reflected light back, go full blast. But that would be then a camera thing, would it not?

Following my tests I should really re-state the problem, as my initial description was not accurate:

- The optical TTL works almost always, when the object is close or even at a medium distance, if it is light colored.
- It fails completely 80% of the time, when shooting dark objects located certain distance away, resulting in full-length strobe discharge . And the background in these shots is not even pitch black or totally absorbing.

This could be also, as Deep Water Dan suggested, a poor quality fiberoptic connection. Perhaps the light conductivity is poor and this has something to do with it? I do not understand the optical TTL control well enough to even evaluate ths option. I don't have a better cable to try, but I guess will do that, eventually.. In my additional tests I did not see dark pictures again, so perhaps this was indeed a strobe charge issue, as DwD suggested.

And ultimately, as Interceptor says, it may not matter at all under water. I will have to wait at least until May to find out for myself. It is still very cold where I am and they are predicting sub-zero temperatures throughout March...