The image not clear

A student obtained a clear image of window grills on the screen . But the teacher told him to get the image of a tree far away, instead of the window . To get a clear image, the lens must be ……………. .

The image of an object formed by a lens on the screen is not in sharp focus. Suggest a method to get a clear focussing of the image on the screen without disturbing the positions of the object, the lens or the screen.

The image of an object formed by a lens on the screen is not in sharp focus.Suggest a method to get a clear focussing of the image on the screen without distrubing the position of the object,the lens or the screen.

Ozone hole is most clear over

A student obtained a clear image of window bars on a screen with the help of a convex lens. But in order to have the best image, his teacher suggested him to obtain the image of a distant tree. Where will the lens has to be moved in order to obtain a clear image?