The change in brightness and a slight shift in the field of view when switching between 2X and 2.5X zoom is due to the differences in light sensitivity between the camera sensors and the position of the lenses. When switching from the main camera to the telephoto lens, the amount of light entering the sensor can vary slightly, which can cause small fluctuations in brightness. Additionally, as the zoom level increases, the field of view changes, which can also affect how the image is framed. This is a normal occurrence due to the optical characteristics of the lenses and the sensor, so there’s no need for concern while using the camera.