Six statements about optical instruments are given below. (i) In normal adjustment, a telescope forms its final image at infinity. (ii) In normal adjustment, a refracting telescope has its lenses $f_o + f_e$ apart. (iii) A longer focus eyepiece raises the magnifying power in normal adjustment. (iv) A compound microscope has the same magnifying power whatever the lens separation. (v) A mirror objective in a reflecting telescope suffers from chromatic aberration. (vi) A Cassegrain telescope has a convex primary mirror. How many of the statements above are correct?