\(\lambda=b sin \theta=b sin \frac{\phi}{2}\)

\(b=\frac{\lambda}{sin\frac{\phi}{2}}\)

\(\phi=30^0\), \(b=\frac{550nm}{sin\frac{30^0}{2}}=2.125\mu m\)

\(\phi=45^0\), \(b=\frac{550nm}{sin\frac{45^0}{2}}=1.437\mu m\)

\(\phi=90^0\), \(b=\frac{550nm}{sin\frac{90^0}{2}}=0.778\mu m\)

\(\phi=180^0\), \(b=\frac{550nm}{sin\frac{180^0}{2}}=0.55\mu m\)