How to improve clarity of narrow-band images (better filters or more integration)

I'm not familiar with the CMOS cameras (I use CCD) but at the very least a cooled camera should improve your images.  More data probably and get yourself an Oiii filter.  A 7 position filterwheel will make life much easier for you so you don't have to keep changing filters.

Carole

There are two things that stick out to me about your post:

1A The first is your statement that "... pixel peeping reveals egg shape but ti is the best I can do with my gear".  I am unfamiliar with your mount, but a quick Bing search revealed that it is not a cheap mount.  You should be able to get round stars with a mount of that expense/quality, especially with subs of only 5 mins duration.  So what might the problem be?  Unfortunately there are many possibilities.  How is your guide scope attached to your telescope?  If it's in a finder-shoe then that might be something to consider.  Are you confident about your polar alignment?  Are you sure everything is tight (but not too tight, of course).  Any cable snags?  What is your Total RMS guiding error?  I would certainly check all of these things before spending any more money.

1B) It could be that eggy stars have nothing to do with your guiding.  I had an (expensive Japanese) scope that was incapable of giving round stars and which (after more wrangling than should have been necessary) had to go back to the supplier.  Could you have an issue with coma?  Before doing any of what I suggest in 1A), I'd check the scope.  Fortunately this is relatively easy to do.  Move your mount so that the telescope is pointing straight up in the air (at the zenith).  Take a handful of short exposures with the Lum filter (5 or 10 seconds, or maybe even less with your CMOS camera).  This will eliminate any guiding errors.  Are the stars round?  If not, then you will have to consider what might be amiss with your scope.

2)  The second thing that stuck out for me was your comment about focus.  Focussing with NB can be difficult due to the limited amount of light getting in.  I'd double check with a Bahtinov mask (on a very bright star) that your focusser was doing a good job of getting focus for you.  Because of the difficulty in NB focussing, many people like to focus with a Lum filter and then apply a 'filter offset' (programs like SGP make this easy to do).  You might have to devote a night or two to calculating your offsets, but then you will save time every night because focussing with an L filter requires much shorter exposures than focussing with an NB.

The other thing to consider is the frequency that you check focus.  I would suggest that it needs to be checked at least every hour.  I refocus depending on the ambient temperature.  At the start of the evening the temperature can be falling quite rapidly, and it is not unusual for my autofocus routine (triggered by a temperature drop) to kick in after each (20 minute) sub during the first hour of an imaging run.

A cooled camera would probably help with noise, but I'm not sure that that is what you meant by 'clarity'.

I hope some of that was helpful.

Good luck.

Steve