Visual report on the 12.5” f/6.5 Teeter Dob with Mike Lockwood mirror.
My eyepiece 'fleet' with the 12.5":
31mm Nagler 67x
24 mm Explore Sci 86x
17.3mm Delos 119x
12mm Delos 172x
8mm Delos 258x
5mm Nagler 413x
6-3mm Nagler Zoom 344x to 688x
The first two nights (Tuesday and Wednesday) of observation were very foggy and absolutely dew-drenched - the most dew I have ever seen. Both nights the main mirror dewed up just after midnight - the joys of a thin 1.1” mirror which tracks ambient temperature very well, I suppose….
Along with the dew was some of the best atmospheric steadiness I have ever experienced. I would place the seeing at 9 to 9.5 (pickering) out of 10. With a 3mm eyepiece (688x) on a 4th mag star near the zenith, the full diffraction pattern was stable and almost unmoving. Unfortunately the transparency was mediocre and, towards midnight, increasingly poor….
The third night (Thursday) was very transparent and drier, with much more manageable dew but the seeing was extremely poor. The close pairs of Epsilon Lyrae were two touching fuzzballs (the night before you could have driven a HumVee through the blackness between…)
I looked at a bunch of double stars the first night… I used my Nagler 6mm - 3mm zoom which gives magnifications from 344x to 688x. Close pairs seen were:
STF 186: sep. 0.8”, mags 6.79/6.84
wide, dark sky split. The dark space was equal in width to the central discs of both components. very delicate first rings were present at all times…
A 1504: sep. 0.6”, mags 8.84/8.92
darkline split. Central discs ‘kissing’… first rings were pretty much too faint to see…
BU 525: sep. 0.5”, mags 7.45/7.47
very deep notch. a black or grey line seemed visible at times..
STF 346 AB sep.0.5” mags 6.19/6.21 This is triple star 52 Arietis. The ABxC pair is at 5” separation… Very nice to see three stars here. The AB pair was a deep notch, again with fleeting glimpses of a line between…
Uranus and Neptune
Uranus showed a perfect, sharp-edged blue-green ball. No albedo features were visible. I was thrilled to see the limb-darkening better than I have ever seen it before. I’m pretty sure I saw two moons, Titania (mag 13.9) and Oberon (mag 14.1), which I determined after making a sketch and comparing to Sky Safari…. Never seen them before!!!
Neptune was equally sharp but half the size and some fainter. Triton (mag 13.8) was dead easy with direct vision…
The rest of the night became too foggy for any success…
Wednesday night I tried to obtain some video lucky imaging of some double stars with varying success. I’m going to process those and put the images up in the double star forum…
Deep sky with good transparency and horrible seeing: Thursday night and Friday night…
A few Planetary Nebulae
IC 1295: 1.7’ x 1.4’, 11.7mag - amorphous, round glow, faint, no central * 172x
Sharpless 2-71: 1.1’ , 13.2mag. - ex. faint. only visible with averted vision…
NGC 6751: 21”x21” - bright, easy, best with 258x. round featureless disc.
NGC 6765: 38” 13.1mag - very much like an elongated galaxy. 258x showed it well
NGC 6778: 25”x19”, mag 12.3, bright, small, oval. best with 258x
Eskimo and the Blinking Planetaries were spectacular!! Words fail!!
Some Galaxies: (these are part of my test for before/after lens replacement in my eyes. Surgery is next week(!) Mags and Surface Brightnesses from Clark’s Visual Astronomy of the Deep Sky.
NGC 7814: v mag 12.0 S.B. 22.4, 119x, easy, elongated, 172x shows stellar nucleus
NGC 128: v mag 12.8, S.B. 21.3, much fainter than previous, 172x shows it well, though.. oval. In the field were NGC 126 and 125 which were both smaller and fainter; 126 needed averted vision….
NGC 147: v mag 12.1, S.B. 24.2, large, very faint, low surface brightness. 119x best
NGC 185: v mag 11.8, S.B. 22.9, large, brighter than 147.. again 119x best
NGC 253: Fabulous! A wealth of detail. Used powers from 67x to 172x.
NGC 278: v mag 11.6, S.B. 20.6, Stellar nucleus, bright and easy at 119x and 172x
IC 1613: v mag 12.0, S.B. 25.6, invisible despite a 30-minute search….
NGC 428: v mag 11.7, S.B. 23.2, Extremely faint. only visible with averted vision…
NGC 628: v mag 9.0, S.B. 22.4, V. faint, barely visible with direct vision, 172x
NGC 672: v mag 11.6, S.B. 22.4, A very pretty open cluster, Collinder 21 is in the field but I never saw a galaxy…
NGC 891: v mag 12.2, S.B. 23.5, This is a larger galaxy but very faint and ghostly. At 172x a hint of the dark lane was visible with averted vision…
NGC 972: v mag 12.3, S.B. 22.0, Never found it…
NGC 1023: v mag 11.0, S.B. 21.5, elongated with 119x and 172x. Central bright star-like nucleus
NGC 1055: v mag 12.0, S.B. 23.6, Extremely faint. Barely visible with direct vision. A bit better with averted vision.
General mirror impression.
At f/6.5 there is only noticeable coma in the outer half of the field of the 31mm Nagler and the 24 mm ES, both 82-degree eyepieces. My ‘Workhorse’ 17.3 Delos shows a tiny bit of coma at the outer edge of the field. With any shorter eyepieces there is no coma.
With the superb seeing of Tuesday and Wednesday night I was able to carefully examine the diffraction pattern at 688x. It is perfectly circular, with no ‘hair’ or other distortions. The first diffraction ring is delicate and thin and, again, perfectly circular. With a 16.9% central obstruction the very great majority of the magic 84% figure (the light in the central disc as opposed to the rings) falls where it should. I have no idea of the Strehl ratio but it is most likely very, very close to 1.0…..
Thanks, Mike. Too bad you won’t be making ‘small’ mirrors like this any more…