The terrestrial telescope has one extra lens more than the astronomical telescope. The extra lens is for

Answer Details

The extra lens in a terrestrial telescope is used for erecting the image. The terrestrial telescope has one extra lens more than the astronomical telescope to provide an upright image, which is necessary for terrestrial viewing. Without this extra lens, the image would be inverted, making it difficult to use the telescope for ground observations. Therefore, the extra lens in the terrestrial telescope helps to erect the image and make it easier for the observer to view the object in its true orientation.