“He looked at me to give the Afghan lens, not simply the objective lens,” Amiri said.
If a piece of ground glass were held at the focus of the objective lens at C, the image could be seen.
When the spot is right and the screen clear, the picture may be focused by adjusting the objective lens.
This tube was parallel to the telescopic barrel containing the objective lens.
In the case of an objective lens, we must turn the side which bulges out most toward the screen and focus in the same manner.
With the objective lens we have two possible focal lengths to consider.