Question

is angle of incident increases angle of deviation decreases but after certain value of angle of incidence the angle of deviation increases what that what is that specific value of angle of incident called does this angle same for all for light of all colours

Answer 1

Screen is just an device or an instrument where the image formed is to be observed. If the screen is removed, the lens will continue to form the image on its focus. Thus, on removing the screen and on looking through the lens in the direction of the object the image of the distant tree is inverted and formed at the focus .

Answer 2

Yes angle is same for all of light of colors