About image formed after light pass through a slit

[OnChi]

What is needed such that the light has to be to create an image on the screen after passing through the slit that is exactly the same shape and size as the slit?

Also, when the image pass through the self made lens but the final image on the screen is so vague and doenst has any similar shape of slit

what factors affect the vividness and same (shape, size) of the image after the light pass through the slit

what should i consider

[Administrator note - your posts have been combined]