More
important, if you decrease focal length, aberrations (both spherical
and chromatic) become more pronounced So, in practice, you
cannot  get a magnifying power of more than 3 or so with a simple
convex lens However, using an aberration corrected lens system,
one can increase this limit by a factor of 10 or so (d)
Angular magnification of eye-piece is [(25/fe) + 1] ( fe in cm) which
increases if fe is smaller