Optics nerds: What's the easiest, lowest cost way to build something that focuses a lot of light from a fairly wide (say 90 degree, give or take a bit) FOV into a spectrometer with a SMA 905 fiber input?
Goal is to collect UV-VIS-NIR spectra of the night sky (particularly interested in both light pollution and auroras) over as much of the 200-1200nm range as I can get with low-cost optics (i.e. I don't want to spend extra to get a bit further outside visible, but will take what I can get easily).
Since the device will be operated outside at night, it can be open frame (no need for any exterior light-shield tube, only mechanical support components).
My initial thought is some kind of 80/20 based frame holding a cheap Fresnel lens at one end, with the spectrometer mounted at the focal point (no fiber, directly bolted to a bracket at the focal point) with a cosine corrector on the input to increase the size of the entrance pupil and provide a bit of tolerance for misalignments.
