The lens equation allows us to understand geometric optic in a
quantitative way where 1/d0 + 1/di = 1/f. The lens equation
essentially states that the magnification of the object = -
distance of the image over distance of the object. So let's talk
about the lens equation, the lens equation allows us to do
Geometric optics but in a quantitative way now it will turn out
that it works exactly the same way for lenses as it does for
mirrors just like Geometric optics does. So I'm going to spend
most of my time talking about lenses because they're easier to
draw the diagrams for, alright so we've got a diagram like this
for a converging lens. Now remember the principal rays we've got
coming in parallel out through focus. Remember that the focus is
on the proper side of a lens when it's converging. Alright then
we've got straight through the vertex no problem then we've got
in through the kind of wrong focus and out parallel. The guys
all meet there's my image everything is wonderful. Now the way
that we're going to