I’ve been trying for days to find ways to adjust the sensitivity of the right thumbstick camera movement (only when zoomed in) and finally figured out what to do. I also found several unanswered questions out there regarding something similar so I just wanted to share what worked for me.
First, make two float variables in your Player Controller blueprint - I called them YawScaleOrginal and PitchScaleOriginal. Set them to Editable, expose and RepNotify for replication. Then setup your zoom with FOV events as the picture goes. While zoom is pressed, the FOV changes to a lower value and the pitch and yaw scale at a 0.x value. Mess around with those values and see what you get! Just remember when unpressed, return the scale values to the original value variables you cast from the Player Controller blueprint.
