Hello.
I didn't run actual program because I don't own any Teensy boards but got interested in lens manipulation and read through the code.

In the circuit diagram (https://github.com/LexOptical/E-Mount/blob/master/circuitdiagram.png), LENS7 is tied to Teensy-PIN0. I suspect this is meant to tied to Teensy-PIN1.

Serial1 is setup as:

E-Mount.ino: Serial1.setRX(0);
E-Mount.ino: Serial1.setTX(LISTEN_ONLY ? 5 : 1);

In short, RX == PIN0 and TX == PIN1.

When you are in NOT LISTEN_ONLY mode,

• Serial1 behaves as TX-only
• Serial2 behaves as RX-only

but TX (PIN1) is not connected to body. Connecting LENS7 to Teensy-PIN1 would resolve the conflict. I guess changing the code like below could also work (again, not tested because I don't own Teensies).

 if (LISTEN_ONLY) {
 Serial1.setRX(0);
 Serial1.setTX(5);
 } else {
 Serial1.setTX(0);
 }