Hello all! Long time lurker here. I'm a bit new to designing setups and end up asking a couple of questions. If not appropriate I can definitely move the thread.
For some context, I am currently making potential observational/imaging setups for my college, with the aim of introducing entry-level undergraduate labs (doing things like cluster photometry, variable star light-curves etc.), and some public visual observation. I'm really hoping to get good equipment to be used for some time, and a setup where I can add things over time. As of yet, I feel I've arrived at a 9.25" - 12" SCT for these functions, and at a CCD like the Atik 383+L (22.5mm diagonal) or Starlight Xpress Trius Pro 964 (16mm diagonal), or a CMOS like the ZWO/QHY 533M (16mm diagonal) or ZWO/QHY 294M (23.1mm diagonal).
With budget constraints, we might have to decide among a Celestron 9.25" EdgeHD, a 10" Meade ACF, and a regular Celestron C-11 SCT. Now, I know that field curvature comparisons for all these scopes have been discussed on various threads. The EdgeHD providing an almost completely flat field and coma correction, the ACF providing some field curvature correction (enough to be almost flat for an APS-C size sensor or smaller) and coma correction, and the C-11 not providing any correction. So we have that aperture vs correction consideration. Other questions that pop in in making the decision are:
- Considering the SCTs' F/10 ratio and the smaller pixel sizes, I think we'd get a reducer at any rate. The 11" EdgeHD OTA retails for about $4400 on OPT right now, while the C-11 OTA retails for about $3200. If I were to purchase the widely praised Starizona 0.7x LF reducer/flattener/coma-corrector for $500, could I have an EdgeHD equivalent for $3700? I realise this topic has been discussed before (here, here, or here), and the general answer is yes. However, does this consensus hold up when we're talking about potential scientific uses?
- Adding to the question above, the cameras we're probably gonna buy are smaller so a full 42mm flat field imaging circle isn't necessary, but my instinct is to future-proof for when we get a larger sensor and accommodate APS sized DSLRs also. In this case, would an EdgeHD 9.25 be better than a C-11 + Starizona x0.7 reducer?
- Alternatively, maybe I am overestimating curvature's effect in doing scientific imaging. In this case, would a regular Meade ACF provide enough curvature correction for this to not matter (for my use case at least)?
- I think we'd get a Celestron Focus Motor (or equivalent primary knob focuser), focusing via the primary mirror. My question is, does the back-focus requirements for SCT with a focal reducer change when focused with the primary mirror (I imagine that since the focal length changes with the primary mirror)? Would that mean I should be prepared to do a lot of back-focus adjusting with some extra spacers? To remove this potential complication, should I forget about primary mirror focusing and stick to image train focusing?
My questions come down to the experienced members here giving their opinion for my use case, and I hope I haven't just facilitated a debate which has been had ad nauseum! At any rate, TIA!