John

I wish I'd kept my 2 inch DGM NBP reading this Obviously it was behaving as it was designed to do. I'll have to look out for another one ....

The diameter of the eyepiece barrel limits the diameter of the field stop which is what defines the edge of the eyepiece apparent field of view. Once the eyepiece focal length gets over a certain length the AFoV just gets smaller and smaller so no more sky is shown, ie: the true field of view remains the same. If you step up to a larger barrel size, you can get the wider fields of view with these longer focal length eyepieces. The is a matter of size and weight to consider though. These are 3 inch accessories:

Pentax is owned by Ricoh now I think. The Ricoh name is included on the boxes of my more recent Pentax XW's and just Pentax on the earlier ones. Having scopes by Vixen and Takahashi I agree that the Pentax XW eyepieces are an excellent match but then again so are all excellent eyepieces

My 31mm Nagler gets used a lot less than my 21mm Ethos and the 40mm Aero ED much less than either. If I observed regularly under very dark skies perhaps the result would be different perhaps ?

You have to try to know And be a skilled observer chasing challenging targets of course ! Most of the time and for most folks the difference will be practically zero I reckon.

Quite possibly. It is still distinctly resolvable even with the 90mm mak-cass but it's a small feature. Jupiters GRS looks smaller to me this year as well.

I expect it up to a point with O-III and UHC filters but, for me, the NBP just took it a little too far. The effect of the filter on nebulosity though was really nice so I'm in two mins whether I should have held onto it. Maybe I'll get a new one and see if the latest coating tech / glass polishing has reduced the effect ?

I had the DGM NBP filter for a while. It is a really effective UHC filter, the best of that filter class that I've used in fact. It does great things with the Orion Nebula extending the "wings" greatly as they curve around and almost seem to meet each other. The Dumbbell Nebula looks really three dimensional with the NBP filter. The only downside with it, or at least the version of it that I had, was the marked splitting of stars into multiple colours. Most narrowband and line filters that I've used do this to some extent but my NBP did it more than any that I've used, to the point where it became distracting. Perhaps the latest versions of the DGM NBP have tamed this effect ?. I hope so because otherwise it seemed a very effective UHC type filter.

Very nice views of Mars with just a 90mm mak-cassegrain and no filter tonight. Dark features form a distinct "Y" shape which includes the Syrtis Major. Bright white "button" of the south polar cap still well defined. Rather hazy skies probably helping to filter the planet naturally. Very heavy dew though - everything is running with it !

One of these: https://www.firstlightoptics.com/uhc-oiii-visual-filters/astronomik-uhc-filter.html

It does work well. My Skytee II is better than my Giro Ercole at carrying my 100mm - 120mm refractors. It even does a decent job with the 130mm F/9 triplet although the T-Rex has now become the primary mount for that scope. Not sure about the wisdom of a Skytee II on an aluminum tripod though I've always used my ST II on at least a 1.75 inch steel tubed tripod.

Of the items you list, my choice would be a good UHC filter to give you something more from your observing. The Baader zoom, in my opinion, will not offer you better performance than the eyepieces you currently have.

Thomas Back's passing was a sad loss to astronomy. Among many other things he designed the objective lens that sits in my 130mm F/9.2 triplet refractor. A really superb performer.

Are they not the same optics as the TMB Paragons ? Maybe those rumours were incorrect ? I find the 40mm pretty good for what it cost. The 30mm is OK at F/7.5 or slower. I use that mostly for outreach.

I would probably add a Rigel Quickfinder in the position I want it. It can be popped off leaving the base in place easily enough when the scope is not being used.