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
