The distance between the two lenses and the convergence of the sunlight can be adjusted by manually moving the cylindrical part of the tube up and down inside the other part and then making fine adjustments by means of a rack screw.
To have the object in sharp focus and sufficiently enlarged on the screen so that its details can be observed, the position of the objective is adjusted by turning the appropriate rack screw so that the object falls beyond the focus at a distance from it of not more than the focal length.