Rules for drawing Ray Diagram in Lenses

There are some rules which we use to obtain images in a ray diagram

Let's look at them

Rule 1 - Ray parallel to principal axis will pass through focus

For a convex lens ,

we see that ray passes through focus on right side

For a concave lens,

we see that ray appears to pass through focus on left side

Rule 2 - Ray passing through focus will become parallel to principal axis

For a convex lens,

we see that ray passing through focus on left becomes parallel to principal axis after refraction

For a concave lens ,

since focus is on the right side,

it appears that ray passes through focus, and then it becomes parallel to principal axis

Rule 3 - Ray passing through Optical Center will emerge without deviation

For a both convex and concave lens,

we see that ray passing through Optical center emerges without deviation