Robin, you are quite right about dispersion..
Last night I obtained my fist spectrum
(used in front of 135mm lens)
I wanted it to be of Alpha Cen.. But, in a hurry I forgot to orient the grating, so I ended up with spectrum of Beta Centauri
(outside the frame).
The spectrum was spread over almost quarter of the frame of my 400D, and 45 sec @ F4 exposure was about right for such a bright star (but it will be nowhere near enough for anything much fainter).
Also, it is contaminated with stars on its path.
Anyway, it was a good exercise :-)
The spectrum plot (Iris) is not calibrated, and axis marks are in pixels (blue to the right). However, some absorption lines are visible, especially in the blue region (where my un-moded 400D is more sensitive, btw) .
Next time it will be better..
Last night I ordered
TE218b to try with brighter spectrum and lower spreading..
In the meantime, I will continue work on my version of Littrow.. This exercise is a good boost for it
