It was a bright sunny day so there was a large difference in light value between the street and the inside of the bus. I set exposure for the street using my largest aperture (f/3.5) and shutter speed at 1/2,000 second. That made for a normal exposure out the windows. The camera body was set to flash in FP mode and the speed light was initially set at full manual power. The flash was mounted in the camera body hot shoe, aimed up and behind me. The bus interior was glossy white paint (a large and harsh reflector). The ride was an hour, and I shot about 100 frames at power settings from full down to 1/8. I couldn't really view the results in this bright light so I relied on histograms.
I wanted the inside of the bus to come close to the exposure level of the street, and I think this picture achieves that. The rear facing flash actually brightened the bottom too much and I pulled a -1 stop gradient in Lightroom to make the light direction seem more normal.
The problem is the composition. I thought a student studing on a bus ride was a cool idea, but it's not working. The frame is cramped and it's hard to tell exactly what we are looking at. The bus windshield is visible in the upper left. Unfortunately a mess of shadows and shapes makes it confusing, and the red seats are just plain big distractions. I can hear the critique already, "Why are you making us look at a seat back and a dash board?" So, yeah, bus insides are hard to shoot. If I get another chance I'll try for more of the window/street view, maybe a horizontal crop.