Difraction Grating + Hartmann Exposes Chromatic Distortion

I was tidying up my laptop after my second (unsuccessful) attempt at deep sky imaging (mist rolled in) and I stumbled across this experiment that I conducted in May last year.

This is am image of Vega - slightly out of focus - with a two hole (small aperture) Hartmann mask and a difraction grating mounted as a 1 1/4" filter.
Thus there are two images of the star and two spectra.

Without the Hartmann mask the spectrum looks fine but the blue end is clearly fish-tailed (I haven't presented an image of this case). With the Hartmann mask the spectra are tighter but curve in opposite directions revealing chromatic distortion at the red end which is not obvious without the Hartmann mask. The scope was my old Meade ETX 70.

I'm sharing this because I find it thought provoking and it might interest others.
1) It would appear that this could be used as a measure of chromatic distortion in optics (e.g., Graph the the distance between any two points - or just eyeball it).
2) Possibly (and only possibly) allow for calibration of chromatic distortion when doing spectroscopy with less than ideal optics.

If nothing else, an interesting phenomena.

Mark