A telescope with objective diameter \( R \) is used to observe a distant star emitting light of wavelength \( 500 \, \text{nm} \), at a resolution of \( 5 \times 10^{-7} \, \text{radian} \). The value of \( R \) is ______ \( \text{cm} \).
\( 61 \)
\( 122 \)
\( 244 \)
\( 305 \)
