
15.6.
Nonobjective Slitless Spectrometers
401
D(m)
Fig. 15.17. Plate factor P at which spectral coma equals seeing blur of
1
arc-sec for nonobjective
transmission grating. See Eq. (15.6.14).
fewer grooves per millimeter. Alternatively, for a given grating at different
distances from the focal surface, the size of TAS is directly proportional to s.
As an example, take a first-order grating with 150 grooves/mm in an//8
beam. This grating has a plate factor of lOOnm/mm when s is 67 mm. At
wavelengths of 400 and 600
nm,
respectively, the astigmatic image lengths are 30
and 68 jim when a = 0. If l^ is 500 nm, hence a = —2.15°, the image lengths ...