What are the three factors controlling circles of confusion?
2-14. CONJUGATE DISTANCE.
The distance between a subject and a photographic lens varies
inversely with the distance from the lens to the focal plane.
distances are called conjugate distance; that is, the total distance from
the subject to the focal plane, (fig 2-20).
When we say that these distances vary inversely, we mean that one
distance increases as the other decreases, and vice versa.
words, when the lens-to-subject changes, the lens-to-film distance must
When the lens-to-subject distance increases, the lens-to-film
distance decreases, (fig 2-21a).
Similarly, if the lens-to-subject
distance decreases, the lens-to-film distance will increase, (fig 2-21b).