Question

A microscope's objective lens produces an image of the target object that forms 165 mm from the eyepiece lens (on the near side of the lens). The eyepiece lens has a focal length of 210 mm. Where does the image appear, relative to the eyepiece lens, from the perspective of someone using the microscope?

In your work, don't just provide the numerical answer that Kudu wants. Interpret what this value actually means.

Answer 1

A microscope is composed of two lenses, an objective and an eyepiece as shown in figure. The object AB (Height h)  forms an image A'B' of height h' which is always greater than h. This first image A'B' (from objective lens) becomes the object for the eyepiece lens. The eyepiece lens forms final image A"B" of height h" that is further magnified. Therefore the objective lens is positioned close to the object to be viewed. It forms an upside-down and magnified image called a real image because the light rays actually pass through the place where the image lies. The eyepiece lens, acts as a magnifying glass for this real image. Fo is the focal length of objective lens and Fe is the focal length of eyepiece lens.

Now given that the real image formed by objective lens is 165 mm from eyepiece lens. This will act as object for eyepiece lens. Also focal length of eyepiece length is 210 mm.

Referring figure above for eye piece lens:

DIstance of object from lens

and focal length

Applying basic focal length formula for eyepiece lens:

(di ' is distance of final image from eyepiece lens)