Re: Transmission grating in a converging beam
I used the Bowen and Vaughan reference, as well as the detailed analysis in Schroeder "Astronomical Optics", p297 to update the focus for the grating in a converging beam in the latest TransSpec spreadsheet..
Schroeder explains the s/3 by working from the Monk-Gillieson arrangement.
He focuses on the TTC to develop his chromatic coma equations and in the end recommends the camera should be tilted to give a "best fit the the curved field.
The resolution of the grating therefore seems to be limited by chromatic coma and out of focus conditions due to the field curvature.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before....