Final answer:
To project a real image onto a screen using a microscope or telescope, move the eyepiece farther away from the objective lens so that the image formed by the objective falls just beyond the eyepiece's focal length, enabling projection.
Step-by-step explanation:
If you want your microscope or telescope to project a real image onto a screen, the key is to adjust the position of the eyepiece relative to the objective lens. Typically, when using these devices for direct viewing, the eyepiece is positioned such that the image formed by the objective lens is within the focal length of the eyepiece, creating a larger virtual image for the viewer. To project a real image onto a screen, instead, you need to move the eyepiece slightly farther away from the objective lens. This allows the image created by the objective lens to fall just beyond the eyepiece's focal length, leading to an image that can be projected onto a screen.
In the context of a microscope, the object being observed is placed just beyond the focal length of the objective lens to create a real, inverted image that is larger than the object. This enlarged image serves as the object for the eyepiece lens. When the goal is to project this image, adjusting the eyepiece further away ensures that the magnified image falls beyond its focal length, making the projection possible. In telescopes, the same principle applies—the placement of the eyepiece determines whether you view a virtual image directly through the lens or project a real image onto a detector or screen.