# Image formation in Ray Optics

Can a refracted ray and a reflected ray form an image( different incident rays coming from the same object, one sufferning reflection and other refraction)? What is the criteria for forming an "image" ? If it doesn't form, what will we see at that point of intersection?

• @Harsh Wasnik , don't comment on any question if you do not understand the question completely. Apr 17, 2019 at 5:38

In general yes they can.

A sharp image is formed if all rays arriving at a specific point of the image, originate from a single point on the object. It does not matter whether they got there directly or by refraction or reflection.

In practice, it is not so easy to come up with a situation where this occurs. One contrived option could consist of a lens, that forms an image on a screen by refracting the light twice and a parabolic mirror that makes an image of the same object on the same screen (you might need an extra mirror to get the image on the screen). If the image from the lens and the image from the mirror exactly overlap, you get a sharp image that is a combination of a refracted and reflected light.

If the two images do not exactly overlap, you get a blurry image.

• The rays must have an optical path difference of a multiple of lambda in the image plane in order to form an image. Apr 16, 2019 at 19:36
• @my2cts this is true and could form the basis of a completely differently formulated answer based on interference. However, my assumption was that the question refered to images made with non-monochromatic light traveling over large distances, in which case the outcome of both methods will in practice look identical. Apr 16, 2019 at 19:51
• If we place a screen on the intrrsection point of the reflected and refracted ray, we get a blurry image, right? Apr 17, 2019 at 5:39
• @user226375 No, we get a sharp image when the rays arriving a a specific point on the screen all originate from the same spot on the object. The rays leaving the object from that spot should thus intersect at the screen. Apr 17, 2019 at 17:37
• @user226375 Do not confuse this with rays that leave the object under a specific angle from various positions on the object. These rays intersect in the focal plane of a lens. A screen placed in this plane would give a blurry image. Apr 17, 2019 at 17:40