Which Teensy are you using? I suggest you try using IntervalTimer, which is built into the T3 and T4 cores, rather than TimerOne, which is a very old library going back to AVR. TimerOne in TeensyDuino does support T3 and T4, but it may not behave...
Thank you @Paul. That did the trick. Thank you for all you do for this community.
For those who end up here with a similar question, here's how I implemented Paul's suggestion...
#define EXPOSURE_TIME 100000 // duration in microseconds for...
Summary
My use-case is a film scanner. Film is constantly moving and, upon detecting one of the holes at the edges, I need to flash LEDs and take a picture to capture the film frame. In this use-case, the timing of each exposure should be as...