Yes, you’re right, the chromatic aberation seems less of an issue with this ‘restricted’ mode of operation. In fact the focus and calibration fit is incredibly good (even for a simple linear fit). Still needs proving ‘at the scope’ though.
That’s great stuff by Terry. The range and resolution looks like a similar config. That gives great hope. Simspec suggests R~ 8000 for an 1800 + H9. See below.
I’m still using ‘not quite the best’ optics but I exacerbated the ‘elephants foot’ problem because I did something really dumb during the design stage…
When I rescaled the camera lens to fit a larger item (same focal length) I unintentionally scaled the base/holder too. This raised the lens off the optical axis. Dopey or what?
I recognised the mistake when I stripped, cleaned and rebuilt the spectroscope ready for ‘final’ testing at the ‘scope. I think I’d been so focused on keeping all the components orthogonal that I’d simply missed it.
Anyway, new holders fitted. That, and more careful placement of the calibration lamp (!), have produced much better results.
Attached below are pictures from both the ‘re-adjusted’ spectros but using a SXH9 camera (1392 pixels) instead of the little Orion. You can still see a small amount of line definition loss but this can be helped with careful lamp placement. Still, I think that’s as far as these optics/configs can be pushed.
Anyway, very peasing results (albeit need to be proved in real life!) but enough success to warrant fitting better optics and a full resolution print. I’d produced some decent test spectra on the few occassions I was able to mount the devices at the scope but there was nothing I’d want to submit. That is, nothing that matched the accepted standard. This gives me hope.
1800 l/mm 30um slit ‘tuned’ to Ha…
Spectro number 1, 600l/mm – 40um slit at 600nm to 750nm…
A ‘refined’ guide image using a 40um slit (which might be to wide a FoV)… I’m still experimenting with different lenses to find the best options – but that won’t happen until I get to use them in anger.