John

No problem Paul.

The bortle 3 skies here in mid-Wales have been mostly covered in clouds. Just one night of observing so far The daytimes have been mostly good though and the Cambrian Mountains really lovely in their early Autumn tints

Decent target here under bortle 5 skies. My 100mm scopes and up show the mag 13 star off to one side of it as well. Needs medium to high magnifications to make it stand out. 250x in the 12 inch dob is V.nice indeed

They don't affect focus position at all because they slide inside the drawtube of the scope. I did need to remove one baffle from the inside of the 150mm F/8 focuser drawtube to give the clearance needed for the chromacor though. The challenge is finding them these days. It was a few years back that I got mine. They are like hens teeth to find now and expensive as well - probably £300 or more. They do really work though and are better than a filter because they actually correct the focus position of the light rays, ie: bring them to focus at very close to the same point, rather than filter them out. The correction of the spherical aberration is something that a filter can't do as well. In all honesty it would probably be better to put the money towards something like an ED120 rather than try and find a Chromacor today.

Me neither and ditto on the Baader / Zeiss prism. Presumably those that are can't use newtonians at all ?

Heilos was the brand name used by the Synta manufacturer before they used Skywatcher. Synta have made equipment for lots of other brand names including, for example, Konus and Saxon. Some of the latest Meade products look like they are made by Synta as well. The Bresser 127L was pretty much exactly the same as the Meade AR5 and I'm sure they were made by the same manufacturer - I've had a Meade and apart from the logo's the scope was just the same. The objective in the Bresser was better though. I never got as nice images with the Meads AR5 as I did the Bresser 127L but I've put that down to sample variation. The Konus 150 F/8 was the first scope that I used a Chromacor with. The Chromacors are optical adaptors correct chromatic and spherical aberrations that are commonly found to varying degrees in these chinese made refractors. Using Chromacor's with these larger achromats taught me a lot about the strengths and weaknesses of these scopes and also the impact that CA and SA have on image quality. If think it's fair to say that using Chromacors eventually drove me to wanting ED doublets rather than achromats. This is one of the chromacor's that I had installed on the diagonal as it needs to be:

Post some pics of your finders if they are optical ?

An ADC is the tool to use if it is atmospheric diffraction and it bothers you. Personally I don't use one. The Feathertouch is in a different class again from the Moonlight - I have one on my LZOS/MB triplet. But the price tag is a heck of a lot I appreciate that. I now have a Vixen R&P back on the ED120SS and find it quite OK. Here are Vixen's instructions for tuning up their R&P focuser and if followed carefully, they do work well: vixenfocuser.pdf

The Meade is the AR6 152mm F/8. The black one is a Helios 150mm F/8 - later they got rebranded the Evostar 150 which is the last one pictured. I also had Konus 150mm F/8 at some point which was the same scope but without a collimatable objective cell. That and a Bresser 127L with the Vixen ED102SS pictured below . I went through a lot of achromats over a relatively short period

A 2 inch wide field / low power eyepiece that will exploit the ST 120mm F/5 refractor capabilities will simply not be useful with the 127mm Mak-Cassegrain as far as I can see

My current "fab four" followed by a few from my past. The big achromats were generally used with a Chromacor CA / SA corrector to produce close to ED doublet performance:

Nice report Vin Great scope and mount - I used to have one ! The red and blue tinges top and bottom might be atmospheric dispersion rather than false colour from the scope. On the focuser, in an F/9.8 scope I think the stock Vixen rack and pinion works well when properly adjusted. If you feel you really need to change you could put a Moonlite dual speed on the scope as I did for a while with my Vixen ED102SS. Your tube is the same diameter as mine:

That's where I would have suggested. I've never seen the DGM NBP offered by a UK based dealer

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.