Glen,
I'm going to throw in a curly one into the mix. There are some DSOs that don't fall into the categories you've listed. Mainly because it is a collection of objects that fall within the field of view of a rich field scope. 'Hybrid's made fun of me with my quirk for getting a true field of view diameter of 10 full moons (5deg)
. Most people would have settled for 9 full moons, but me, nah, it HAD to be 10!
It is a real niche within visual astronomy, and one that I've only discovered the flavour for in the last couple of years, "Rich field observing". While I have scopes going up to 17.5", my latest scope has gone the other way, down to a 4" f/5 refractor. With it I see not only a bigger picture, but in many instances it is the only way to view dark nebulae.
The best part about rich field observing is it is probably the easiest of the lot - being low magnification, steady seeing is not critical; cheap, fast achromats are perfect, this include binos; being wide field, Earth's rotation affects things much slower. Rich field observing is probably the least mentioned, yet binos are one tool most recommended.
So, these are my "5" favourite rich field areas (alas at the moment I've only got a couple of sketches of these):
*
Eta carina to NGC 3532 - a mighty nebula and a might open cluster. And the surrounding environment is a dazzling mix of star clouds, smaller clusters and dark nebulosity. The first sketch if of this area done from my home in Sydney with 11X70 binos. From a dark site, it is even more impressive.
*
M8 to M20 - an Autumn show piece. The extent of nebulosity of M8 is astounding, and with M20 and M21, a wedge shape is curiously formed, reminiscent of the Hydes. The biggest surprise though comes from using a rich field scope and the star clouds and the finger like dark pillar that sits at the edge of the field of view that never otherwise is seen. This is the second sketch with 11X70 binos from a dark site, and the third sketch from home with an 8" f/4 scope at 26X.
*
Table of Scorpio - A cracker-jack collection of open clusters, dark nebulosity and background Milky Way. The asterisms that the stars and clusters form as a whole create their own shapes - one such 'picture' is of an anchor that fills the FOV.
*
LMC - One thing is to examine this monster micro-wise with a scope. Another is to go WIDE and macro, taking in as much as possible. Countless DSOs then fill the FOV.
*
Area around M42 - Sensational! From a dark site and an RFT, the nebulosity of M42 extends further. And then there are the other DSOs and background Milky Way adding their own touch. WOW!
I too was guilty of running rough shod over these areas with my binos. Today, it's another story. Next dark sky session for me, the 17.5" will be staying at home. I'll be taking only my 4" refractor on one eyepiece. Nothing more. Oh, yes, and my sketching gear...
