(a) The angular size of the image is equal to the angular size of the object. By using a magnifying glass, the object can be placed much closer than 25 cm. The closer object has larger angular size than the same object at 25 cm. Thus angular magnification is achieved.
(b) The angular magnification changes, if the eye moved back. It decreases a little because the angle subtended at the eye is then slightly less than angle subtended at the lens.
(c) First, it is difficult to grind lens of very small focal length. Secondly, if we decrease the focal length of a lens, both spherical and chromatic aberrations become more pronounced.
(d) Angular magnification of eyepiece is (1 + d/fe) which is greater if f e is smaller. Magnification of the objective lens is given by v0/u0.
The object is held close the focus of the objective lens
∴ u0 ≈ f0.
Therefore magnification is v0/f0. As the u0 is small, so is f0.
(e) The image of the objective in the eyepiece is known as eye-ring. If we place our eyes too close to the eyepiece, we shall not collect much of the light and also reduce our field of view. The location of eye-ring depend on the separation between the objective and the eye piece.