can't really understand TTL fiber-optic cord function

[Ahmed Yahya]

Hi
i have a question regarding the TTL function when using strobes with pop up flash. i am planning to get the Olympus EPM-1 in Olympus housing with Sea&Sea YS-01 strobe and fiber-optic cord. does the strobe actually changes flash exposure automatically through TTL measurements ? or it just fires at fixed power every time the pop up flash fires ?

 

[Matt S.]

In TTL mode, the camera monitors the incoming light (Through The Lens), and quenches the flash when it has collected enough light. So, the total power output from the external strobe does vary.

 

[Ahmed Yahya]

In TTL mode, the camera monitors the incoming light (Through The Lens), and quenches the flash when it has collected enough light. So, the total power output from the external strobe does vary.

but how the strobe KNOWS at what power should it flashs ? does the fiber-optic cord sends the flash power of the camer's pop-up flash as well ?

 

[Matt S.]

The strobe goes off at the same power level all the time, but how long it stays on changes. The total flash duration is still very, very short. It's much faster than the shutter speed even if the flash does a full power dump... I think it's something like 1/10,000.

Technically you can adjust the power level too--there should be a dial on the flash for power tweaking. But I do not think that the camera "tells" the external strobe how bright it should be through the fiberoptic cable. It's a simple on/off signal.

I am sure someone will be along to correct me if I'm wrong!

 

[JohnN]

. . . with Sea&Sea YS-01 strobe . . .

Just a word to the wise, the YS-01 does not offer TTL. In one of their less that stellar moments, after it was released, they discovered their error and rather than fixing the units already sold, they released the YS-01a (alpha).

That is the main reason for the price differential between them

 

[Ahmed Yahya]

i couldn't find any alpha model of YS-01 in sea&sea site, may be they fixed it. but even with the YS-01 or any other model, i am still not sure how the TTL works with fiber-optic cord or if it even offers true TTL.
i have a Nikon D7000 DSLR with SB-900 flash and i know how TTL flash exposure works. even with the wireless slave function of SB-900, the camera sets the correct flash exposure through the preflash measurement.
that means if YS-01 strobe is offering true TTL flash exposure, it should emit preflashes and receives the flash power setting from the camera body and all this communication should go through the fiber-optic cable.
is that what actually happens ?

 

[herbdb]

I have an Olympus EPM-1 and two Sea and Sea YS-01 strobes. I tried the TTL mode on a trip to Bonaire last month. It seemed to function, but the pictures were uniformly overexposed. By this I mean that a night photo was overexposed about the same amount as daylight shots.

I did not try adjusting the level on the strobe, because as I understood the documentation, the knob had no effect in TTL mode. The TTL mode controls the amount of light by adjusting the strobe flash time after evaluating a preflash.

There is an adjustment within the camera to reduce the exposure by set amounts. I am going to experiment with it when I have a chance.

 

[JohnN]

i couldn't find any alpha model of YS-01 in sea&sea site, may be they fixed it. but even with the YS-01 or any other model, i am still not sure how the TTL works with fiber-optic cord or if it even offers true TTL.
i have a Nikon D7000 DSLR with SB-900 flash and i know how TTL flash exposure works. even with the wireless slave function of SB-900, the camera sets the correct flash exposure through the preflash measurement.
that means if YS-01 strobe is offering true TTL flash exposure, it should emit preflashes and receives the flash power setting from the camera body and all this communication should go through the fiber-optic cable.
is that what actually happens ?

Apologies. I was thinking of the YS-110 strobe. Sorry for the confusion

 

[Ahmed Yahya]

I have an Olympus EPM-1 and two Sea and Sea YS-01 strobes. I tried the TTL mode on a trip to Bonaire last month. It seemed to function, but the pictures were uniformly overexposed. By this I mean that a night photo was overexposed about the same amount as daylight shots.

I did not try adjusting the level on the strobe, because as I understood the documentation, the knob had no effect in TTL mode. The TTL mode controls the amount of light by adjusting the strobe flash time after evaluating a preflash.

There is an adjustment within the camera to reduce the exposure by set amounts. I am going to experiment with it when I have a chance.

this is a very valuable information for me as I am planning to get the same set. can you try the bundle on land ? i mean put everything together as if you are diving and try to shoot some photos on daytime and night and see how they come.