I teach physics at a community college, and for use in our lab course we have a nice set of 1960s spectrometers that each contain a telescope. (For a description of the optics, see my lab manual, lab 14, p. 62.) The telescope has an eyepiece that fits into a 49/64 inch diameter hole and seems to have a focal length of about 2 mm (I haven't been able to find an exact figure). The manufacturer is still in business and sells the eyepiece as a microscope eyepiece (their part number M240).
The students line up the telescope by eye on a spectroscopic line using crosshairs, and read the angle from a vernier scale. I think I could actually save a lot of time and effort, and get a better educational experience for my students, if I could replace the eyepiece with a digital camera. I would take a double exposure of a calibration spectrum and the unknown spectrum, for a case where the calibration lines were visible in the same field of view as the lines with unknown wavelengths that are to be determined.
So the only thing is that I need some kind of inexpensive digital camera that can be adapted physically to a hole of this size and has a ~2 mm lens, manually adjustable focus, and manual control of exposure. The supplier sells something like this for $850, which is way out of my price range. Would it be possible to adapt a $50 USB microscope or el cheapo telescope camera for this purpose? It seems that 49/64" is not a standard size for a telescope eyepiece. Cheap USB microscopes seem to be designed for little kids to hold them in their hands and look at leaves and bugs.