YS110 Calibration - Part 3

I had established a minimum and maximum quench interval for my YS110 (actually I was using a YS110a, but I assumed both models have the same flash tube and capacitor specifications - oops!). All I had to do was replace my linear map with something that reflected the reality of Flashtube discharge curves.

My initial urge caused me to ignore the practical world and instead wander down the theoretical path. What kind of curves was I dealing with? This caused me to dig out my old CRC Standard Mathematical Tables and Formulae book. Not much luck. I did not find an obvious or simple match to the strobe discharge curves. Maybe I was over thinking this? Even if I found a formula, how was I going to establish the values for the parameters?

Time to step back once again and think. I needed to produce a set of quench delay interval values that would produce the proper amount of light that corresponded to a normal Exposure Value scale**. I quickly realized that there was no hope of being able to verify my raw interval vales with any available information. There was no standard reference. Every strobe model would have different characteristics. And all of this information was private to the manufacturer. The only thing I could compare was the actual strobe light output itself.

Bingo!

I could produce my own reference data. All I needed was a set of pictures taken at the different power settings of my existing strobe. I could use this reference set to compare to my own power map.  And then fiddle my delay map until they matched. I had a valid repeatable scientific approach. The only flaw was that my measurement criteria was subjective. I lacked proper laboratory equipment to perform an objective scientific comparison - I would have to subjectively eyeball each set of pictures...Not perfect, but maybe good enough?

All I needed was a light sensitive set that could be used to visually gauge and compare the light level. I was unaware of any commercial product or even the proper way to do this. But since scuba strobe photography is all about the distance to your subject, I reasoned that distance would be key. So I created a simple strip out of duct tape, made marks every foot and pasted some tiny white Avery label spots along the length of the strip.    

I created my reference pictures by putting the strobes (I used a pair) into manual mode and took a picture at each power level. By using the controls on the strobes I was able to create a set of pictures that slowly revealed more (further away) detail in each picture. Special note: One of the strobes screwed up on one of these reference pictures and obviously way over exposed. Buggy firmware...Sigh...

I then launched into a set of iterative experiments where I took a set of pictures based upon my current quench delay interval map and then visually compared that set to my reference set.

It immediately became obvious (as predicted by the flash discharge curve information) that the majority of the strobe light was discharged very quickly. My original linear map had its second picture matching one of the last pictures of my reference set.

More work was required...

** And this may be a bit of a white lie. The Sea & Sea TTL converter manual provides the following disclaimer: "The TTL adjustment range value (-2.0 to +2.0) is designated by SEA & SEA, and is different from the EV value". The manual for the YS110 and YS110a are silent about this topic. I did find current strobe product specs that referred to standard EV GN numbers for the manual strobe power level settings.