The reason for this thread is to identify an adequate scope for pure narrowband imaging. As many would know, narrowband with its thin slices of spectrum is supposedly more forgiving of glass colour correction fidelity. Achromat optical designs have been used successfully for narrowband, and I have myself used a Bresser 152S for narrowband imaging with good results. The Bresser 152S is augmented with a rear mounted Petzval elements, hence it is a sort of modified Achromat.
There are plenty of threads, hundreds probably, that debate the optical design and glass types, best chosen for broadband imaging. People love to argue about that subject, but little discussion is dedicated to pure narrowband scope choices. And let's face it, for many people narrowband is the only choice if they want to image; given their light pollution situation, or preference for the billowing details that narrowband imaging provides on emission nebula.
So, let's have some discussion on this topic. Sure a great APO, or even your wonderful Newt can be used for narrowband, but that is not really what this is about.
Consideration to field correction should be given, so possible Petzval or corrector designs have some advantage, but add-on flattener can be an option. Speed is another attraction, as we all know narrowband can take some time to build.
Suggestions, recommendations, and remember keep the purchase price as low as possible, and keep emission nebula targets in mind.
