A high-resolution grating 260 mm wide, with 300 lines per millimeter, at about 75° in autocollimation has a resolving power of just about 10⁶ for λ = 500 nm. Find its free spectral range. How do these values of R and (Δλ)_fsr compare with those of a Fabry–Perot etalon having a 1-cm air gap and a finesse of 25?