I was testing the flash sync wrong on every focal plane shutter for a year
I always ran the flash at the marked sync speed and assumed if the frame looked black at the edge the shutter just needed a clean, so I turned down maybe 20 jobs before a guy in Portland told me to check the curtain travel with a slow-mo clip on my phone. Turns out the second curtain was closing a hair early at 1/60 and the trailing edge was getting clipped by the curtain, not the flash timing at all. How do you all catch curtain drag before it eats your flash shots?