protected void zoomCamera(float value) {
        if (cam.isParallelProjection()) {
            float zoomFactor = 1.0F + value * 0.01F * zoomSpeed;
            if (zoomFactor > 0F) {
                float left = zoomFactor * cam.getFrustumLeft();
                float right = zoomFactor * cam.getFrustumRight();
                float top = zoomFactor * cam.getFrustumTop();
                float bottom = zoomFactor * cam.getFrustumBottom();

                float near = cam.getFrustumNear();
                float far = cam.getFrustumFar();
                cam.setFrustum(near, far, left, right, top, bottom);
            }

        } else { // perspective projection
            float newFov = cam.getFov() + value * 0.1F * zoomSpeed;
            if (newFov > 0) {
                cam.setFov(newFov);
            }
        }
    }
Zoom the camera by the specified amount.

@param value zoom amount
jme3-core/src/main/java/com/jme3/input/FlyByCamera.java