An objective with semi-aperture angle α is first used in air (n=1) and then with immersion oil of refractive index 1.5, keeping α unchanged. How does the minimum resolvable distance change?
a) It remains the same.
b) It becomes 1.5 times the previous value (resolution worsens).
c) It becomes 1.51 times the previous value (resolution improves).
d) It becomes 2.25 times the previous value.