In this photo from 1926, we see George A. Van Biesbroeck (1880-1974), an astronomer at Yerkes Observatory, observing Mars when it approached close to the Earth that year. Van Biesbroeck is shown using the observatory’s 40 inch refracting telescope, the largest of its kind in the world.
A refracting or refractor telescope is a type of optical telescope that uses a lens as its objective to form an image. The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses. Although large refracting telescopes were very popular in the second half of the 19th century, for most research purposes the refracting telescope has been superseded by the reflecting telescope.