Inon sTTL question

[Jongwon Woo 0]

manual mode, same shutter speed, optical cable

 

Camera flash (above)

D2000 strobe (below)

 

http://blog.naver.com/jongwonwoo/10089784658

 

 

 

Those two pictures should be identical, if sTTL works as Inon told.

 

Is it just my strobe's problem or the failure of sTTL?

 

What's your opinion?

 

(I've been using this strobe since I started taking u/w photos and quite satisfied with its performance so far.)

Edited July 9, 2010 by Jongwon Woo

[tdpriest 115]

Clearly, some failure of sTTL. Have you checked the magnet setting? Power setting on the strobe? If the background is a long way behind a small subject then overexposure is also likely, but here you have a general over-exposure. If the strobe is very close to the subject this can happen if there is a minimum strobe duration (ie a minimum light emission that can't be further reduced). Underwater this is unlikely because the light absorbtion is so much greater.

 

Tim

 

[Jongwon Woo 0]

Thank you, Tim.

 

Magnet and power setting were as usual. I'll try one more at faster shutter speed. (The pictures above were taken at relatively slower shutter speed...)

 

Another question : if it's due to the failure of sTTL, what about non-Inon strobes? Some Sea&Sea strobes can be fired by optical cables and they are told that TTL works.

 

Moreover, will this failure not happen when using Ikelite strobes with sync cord or using Sea&Sea strobes with TTL converter & sync cord?

[CADiver 2]

Let me GUESS ...

 

You are expecting the 2 pictures to have similar exposure result ?!

 

You care comparing the result of a picture lit by the Canon onboard flash against a picture lit by the Inon via sttl from the Canon onboard flash.

With that said, my understanding of the Inon sttl basically duplicate the amount of output send to the flash, if the onboard flash is going at 100%, the Inon will detect 100% and fire at 100%. That doesn't necessary make the 2 pictures exposure identical, isn't it ? The Inon flash probably more powerful then the onboard flash, where you place the Inon during the test might makes the different too, isn't it ? Direct angle vs outside angle etc etc. The manual had an entire section describe how it may over expose or under expose depends on the situation, it may help explain your experience.

 

I am sure other more knowledgable folks will hopefully correct me, I think it's comparing apple and orange a little bit.

 

Thanks!

Dominic

[bvanant 189]

manual mode, same shutter speed, optical cable

 

Camera flash (above)

D2000 strobe (below)

 

http://blog.naver.com/jongwonwoo/10089784658

 

 

 

Those two pictures should be identical, if sTTL works as Inon told.

 

Is it just my strobe's problem or the failure of sTTL?

 

What's your opinion?

 

(I've been using this strobe since I started taking u/w photos and quite satisfied with its performance so far.)

A lot will depend on how you set this test up. What camera, and at what shutter speeds, and at what aperture. In my tests with a 7D and Inon strobes, at very low fstops (like f2) and bright ambient, the Inon can not physically quench fast enough to properly expose the picture. In the camera, you can set the strobe power/duration with much finer resolution than you can set the Inon. Remember that the TTL does not set the power of the strobe but rather how long the flash can last. Sometimes if there is lots of ambient light then the strobe can simply not put out a short enough pulse of light to properly illuminate the scene.

 

Try this test

Set up your subject so that if you shoot it without the flash (f16 and 1/200 sec if you can) then the picture is essentially black. Then repeat with the camera flash and the Inon. My guess is that they will be much closer then what you have shown.

 

Bill