In my recent review of night vision with my Tec160fl, it was suggested that I try to observe some globs using a much slower system speed than I normally use in order to get more image scale.
For emission nebulae I still believe system speed (coupled with very narrow ha filters) is king for my preference of showing as much nebulosity as possible - I’m not too worried if stars get attenuated.
But for point objects such as globulars I can see that slower systems may work better.
From several discussions with other nv users I’ve come to realise that personal preference varies quite considerably and I suspect this is another area where this is the case. Nevertheless, we had some clear skies last night (with a full moon blazing, so challenging conditions) and I decided to doa it of experimenting to see what I preferred.
I used my 95mm refractor and initially used a 41mm panoptic (on m13). This gave a system speed of f3.7 and a magnification of 13x. M13 was small but nice and bright and easy to resolve stars.
I then switched from the 41mm to an 18mm delite which gave a system speed of f8.5 (far slower than I would normally use) and mag of 31x.
The view of m13 was materially dimmer as expected, and my initial conclusion was negative. However, with extended viewing more stars came into view and the propellor was clear which pleased me given the small size of the scope. I gradually came to appreciate the view. I’m still a keen advocate of using fast systems with nv but this experience has meant that I am now more open to trying alternative eyepieces to get more image scale. Certainly I’m looking forward to get 100x mag with the c11 on m13 from a dark site - I think that could be a special view.
I took some smartphone shots (first one is iso 50, exposure time 10 secs and second one with the satellite trail is iso 50, exposure time 8 secs). Both with an astronomik 642 filter which worked very well even with the heavy light pollution and full moon.
There’s been some discussion about the long eyepiece stack with afocal nv being a big issue. Well my reducer, plus pan 42 plus nv monocular was quite some stack (see third image) but presented no issues for me or the scope focuser last night even at the high altitude of m13.
As a test of the transparency last night (after the disappointing views with the tec recently) I had a scan around with my nv monoculars, narrow ha filter and 3x afocal lens. Pleasingly this worked exceptionally well (with an sqm of 17.8). The views of Cygnus got close to views I’ve had a dark sqm 21 sites. The narrowband ha filter really helped here. The NA nebula was very bright and defined as was the pelican. Gamma cygni was also very bright with lots of detail showing and crescent nebula clear even though the mag was only 3x. Lots of fluffy nebulosity over the top of the NA and gamma cygni as well.
Moving round to Sagittarius, and these really were spectacular last night. The eagle and swan were very bright and defined with the 3rd patch of nebulosity above the eagle also clear.
Most compelling of all was the detail shown on the lagoon (even though it was only 12 degrees or so and only just peeking over the top of my neighbours roof). At only 3x, the middle lane was clear and further swirls were shown together with the nebulae extension to the left. I think transparency was very good last night after the heavy downpours we have had this week in the UK. But given the lp, the results with the fast f1.4 3x afocal lens were exceptional imo.