An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of

Options

A. Large focal length and large diameter
B. Large focal length and small diameter
C. Small focal length and large diameter
D. Small focal length and small diameter

Answer

A

Explanation

Angular magnification = `(f_(0)/(f_(e)`
So, focal length of objective lens should be large for large angular magnification.
Angular resolution `((D)/(1.22lambda))`
So, objective should have large diameter (D) of objective lens for large resolution.
Hence option (a) is correct.