Third-person distance zoom:

distance -=
    scroll * zoomSpeed;

distance =
    Mathf.Clamp(
        distance,
        minDistance,
        maxDistance
    );

FOV zoom:

playerCamera.fieldOfView =
    Mathf.Clamp(
        playerCamera.fieldOfView -
        scroll * zoomSpeed,
        minFov,
        maxFov
    );

Orthographic zoom:

playerCamera.orthographicSize =
    Mathf.Clamp(
        playerCamera.orthographicSize -
        scroll * zoomSpeed,
        minSize,
        maxSize
    );