Smallest angle that can be resolved by telescope is given by dθ=‌
1.22λ
D
Smallest angle that can be resolved by human eye is given by dθ′=‌
1.22λ
De
where, De is the aperture of human eye, therefore the telescopemust have a minimum magnifying power which must be such that if an object subtend an angle dθ at its objective, the final image produced must subtend an angle dθ′ at the human eye. ∴ Minimum magnifying power is given by M=‌
dθ′
dθ
=‌
D
De
⇒M‌‌=‌
100cm
0.2cm
‌‌=500‌‌‌‌[∵D=100cm‌ and ‌ De=0.2cm‌ (given) ‌]