After much internal ruminations, I need some feedback
I'm looking to get a low cost (but acceptable quality), portable refractor for primarily rich/wide field visual observations (open clusters, large nebulae, comets, sky scanning etc.).
I'd like it to be something that will slot in between my Celestron Nexstar 8SE (which I use as a workhorse for planetary and smaller DSO visuals and short-exposure astrophotography and imaging) and my 15 x 70 binoculars, which are great for really wide-field stuff and grab'n'go.
I'm looking at the Skywatcher/Saxon alt/az models, either the 120 or 102 f/5 achros, but am open to other suggestions (though I want to keep in under $1000 budget, preferably well under -- if I want to get serious about a refractor in the future then I'll get a proper APO when the time is good and proper
).
My indecision is largely over the aperature vs focal length trade-off. For instance, take the a scenario using the following 3 EPs that I own: TV 24 mm Panoptic, 16 mm Nagler and 11 mm Nagler.
For the 120 mm (600 mm FL), I would get the following TFOVs:
24 Pan = 2°35' at 25 x magnification (yields a nice 4.8mm exit pupil)
16 Nag = 2°7' at 38 x (3.2 ep)
11 Nag = 1°25' at 55 x (2.2 ep)
For the 102 mm (510 mm FL), it would be:
24 Pan = 3°2' at 21 x magnification
16 Nag = 2°29' at 32 x
11 Nag = 1°40' at 46 x
So obviously the 102mm gives the wider field (but still well below my binoculars at 4°24', so it 'fits' nicely (my 8SE with the Panoptic and a 0.63 FR gives 1°13'). The 102mm is cheaper (costs $150 less than the 120), and probably is more steady on the AZ3 mount.
However, the light gathering capacity of the 120mm is much better (an alluring 38% more than the 102!), and it can resolve to 58 arcseconds vs 73 for the 102 (I minor consideration here, I know).
All in all, it's a tough trade-off. Have I missed any other factors? What do do??
