I'm just at the threshold of amateur telescope making (my copy of Texereau's "How to Make a Telescope" is currently in the mail), and although I am some way off yet from building the reflector telescope that I really want (I see many iterations and smaller scopes in my future), I am already thinking about that final design. I came across the topic linked below in the ATM forum that discusses how well different optical telescope designs compare in correcting off axis abberations in astronomical images. My question is related to that topic but is somewhat flipped around. I am primarily interested in spectroscopy of point sources, so a telescope design that provides image correction over a wide field is not strictly necessary; in addition, a minimisation of the number of optical elements would beneficial by increasing the throughput of the system. With this in mind, is it known, or possible to calculate, the size of the on-axis region that is free of image aberrations for a given telescope design? I understand that this is likely a complex problem with multiple factors at play, but if this is documented, or if there are known ways that can be used to work this out I'd be very interested in knowing more.
Thanks for reading!