f-Stop f-stop = f/D
Focusing - operation of placing the lens at the correct position relative to the film for the sharpest image. To focus on nearby objects the lens must be moved away from the film.
Depth of Field For a given distance setting, there is a range of distances over which the circles the confusion will be small enough that the images will be reasonably sharp.
Conceptual Example: Shutter Speed To improve the depth of field, you stop down your camera lens by two f-stops from f/4 to f/8. What should you do to the shutter speed to maintain the same exposure?
Farsighted Eye A particular farsighted person has a near point of 100 cm. Reading glasses must have what lens power so that this person can read a newspaper at a distance of 25 cm? Assume that the lens is very close to the eye.