During a lightning storm at 3am. My understanding of shutter speed, and how it relates to aperture and how they in turn relate to iso and letting light onto the sensor. Really not a difficult concept now that I think about it, but easier understood after trying to photograph my first lightning storm. I got about2 really good ones, and a bunch of okay ones from it. But most of all I think I am ready for next time! If anyone wants to learn about how these settings relate to each other, do some reading and go photograph a storm at night. It was excellent practice and I feel like a more capable photographer now. I'm glad I got out there! There is one photo I posted in the potd thread that is my fave. They are not as good as the seasoned nature photographer's efforts but it was cool to get strikes saved !