Last weekend I had the pleasure of getting first light on a new-to-me dob with a 16" f/4 Lockwood mirror. This is actually my first Dobsonian, but is almost certainly not my last. I have wanted one ever since middle school, when my buddy got an 8" Coulter for Christmas from his deadbeat dad. Now, decades later, I've finally got one of my own (albeit, lacking that classic red Sonotube look...)
Almost all of my night vision gear was on loan out to Okie Tex, so all I had was my White Phosphor PVS-7C, a C-mount adapter nose for it, and a 6nm H-alpha filter. Of course this being first light, I also brought all my regular eyepieces and such.
Eddgie met me out at the observing site with his Mod3c, PVS-7, and Boren Simon.
The moon was over half full and, unfortunately, glowing bright near the Southern Milky Way region. The evening was also somewhat hazy and quite dusty, and there seemed to be much more light pollution at the site even though I had great dark skies earlier in the spring from this same location. Austin is one of the fastest growing cities in the country, so I'm afraid we're suffering from a little bit of that, even out in (what used to be) the countryside.
I decided that my first target would be Saturn, even with it being low in the sky and awash in light pollution. Although we could easily see it at low power, there was simply too much atmospheric distortion for it to present much of an image at higher power. Despite all of my fascination with NV and EAA, getting high-resolution views of planets is also one of the reasons I wanted to get a bigger scope.
Anyways, since the air was so hazy and there was so much light pollution, I decided to look towards zenith and hit the popular objects in Cygnus. This is when I first realized that the scope would not reach prime focus for the Mod3. So, we reconfigured for (handheld) afocal projection, and the 41mm Panoptic presented a good-sized field in this scope. The North America and Pelican region showed a lot of nebulosity despite the bad transparency. They were too large to fit into the FOV, but the California region in particular did show up pretty brightly.
Since I've been over this region quite a bit with my C11 (reduced down to f/5), I have a baseline expectation of the visual appearance. Now, on this night it wasn't a side-by-side comparison, but it did seem to me that in the 16" scope, more subtle "gradations" of nebulosity was visible. It's hard to describe, but with my C11 under light-polluted skies, the contrast between faint nebulosity and black sky is harder to ascertain. With the 16", even using a slightly narrower-band filter (6nm vs 7nm in the C11), when I was looking at a region with nebulosity, I know that there was "stuff" there, even if it didn't have a lot of structure.
In a different thread, Eddgie talked about how we saw the Elephant Trunk, and how I managed to place it dead-center in the eyepiece even though I didn't "see" it until he looked more closely and confirmed that it was there. I basically scanned the scope around the background haze of nebula and pointed it at the region of what appeared to be the densest part - and lo and behold that happened to be where the trunk was.
After the North America, I put the scope on the Crescent Nebula and it presented really nicely. There was so much structure present in the middle of it! I believe we used a Nagler 22mm for this, but I don't recall if we went up to the 14mm Delos on this.
Then we moved over to the Veil, and it was so nice... We could see lots of structure throughout, and Pickering's triangle showed great structure as well. I didn't push the magnification up as high as I did earlier in the year with my C11 under dark skies, but with the 16" under mediocre skies (and bright moonlight), I was not going to complain. The Veil is always a delight.
I moved over to look at Albireo through plain glass, and the colors shone through beautifully. They were perfect little pinpoints of bright color, just marvelous. When I defocused and they were large Airy disks, their colors actually seemed to present more brightly: one bright golden disk, and one bright blue. I have to admit I kind of enjoyed that out-of-focus view - it is just so unexpected to have that much color bursting at you through the eyepiece! I also made a mental note that with the larger scope, I need to look for natural color in nebula, clusters, and stars, since it may be enough light grasp to exceed the threshold of sensitivity in my eye.
I decided to try for the Swan and Eagle nebulas, despite the fact that they were completely lost in hazy skyglow and moonlight. I had to look through my Telrad with the PVS-7 in order to locate them. I was pleasantly surprised at the Swan: It looked pretty good, and we could see the mottled patches of nebula in its chest. The extended nebulosity around it was hard to see, given the conditions. Night vision can cut through a lot of stuff, but this was a tall order. The Eagle Nebula was easy to see, but the Pillars and the central dark region was lost in the mush.
I am really, really looking forward to visiting these objects again in a few weeks when we go camping under a new moon out in west Texas!
Next, we looked over at Cassiopeia. As my first target, I wanted to look at the Pacman nebula at larger scale. I remember looking at it in my C11 but it's not one of my popular objects because it generally shows up as just a featureless blob. However, in the 16" Dob, it took on real structure and personality. I seem to recall Eddgie was also struck by that. The "upper lip" of Pacman was distinctly brighter than his body, and clearly extended/protruded beyond the circumference. I don't recall seeing much other structure (or even his eye, in fact..), but that part stood out the most for me. I think that just as with the Elephant Trunk, dark nebula or dust inclusions are much tougher to see in light pollution.
I also tried to look at the Heart and Soul, but it was just too large to fit in the scope. There was plenty of nebulosity and some structure, but the image scale wasn't quite right, and contrast wasn't great for these nebula on this particular night.
Next up, we looked at the Double Cluster with bare glass, and that was a very pleasing sight. We also went for M13, which was very low in the sky and also lost in the skyglow of downtown Austin. I had to (once again) use my PVS-7 through the Telrad to find it, and visually in the eyepiece, it presented as the barest smudge of fuzz against a bright background of light pollution. But sticking an unfiltered Mod3 into the light path brought out the cluster in all of its glory. Not my best view of M13 by a long shot, but still a neat trick.
I then looked over towards Auriga and scanned through its central region around the Flame Nebula. Once again, the light pollution made it difficult to observe much interesting structure in this area. In the 16", I could easily see there was a ton of nebulosity, but the subtle ripples and tendrils were lost in the the LP. One interesting thing I did find was a small patch of nebulosity up towards the Kids. I could see it at 1x, and could sight it in the scope. It didn't yield much structure, but it was distinct and present. Sky Safari doesn't show a name for this object, although the H-alpha Milky Way background clearly show it as a bright area. It is near NGC 1857, and shows up clearly in this photo (it is the small circular nebula at top, right of center): https://www.mdwskysu...=style-j40p46pn
Lastly, we saw that M42 and M43 were right on the horizon, just rising. As a preview of what I can look forward to later this year, I decided to have a look. It was all pretty washed out, and it was hard to see even 4 stars in the Trapezium (the faintest one was blinking in and out due to atmospheric distortion). But the rectangular glowing center of M42 did shine through all the crud and was quite exciting to see... a good omen of a fun fall and winter viewing season!
So in summary:
- Yes, aperture matters - even with Night Vision!
- Also, Night Vision is not totally magic: really bad light pollution and haze will limit the efficacy of even a 16" light bucket.
- Afocal viewing was not unpleasant, and for scopes that can't reach focus for prime focus, it's a fine approach. The big caveat is that I have a decent collection of Televue glass, and the new TV Mod3/PVS-14 adapter only works on TV glass. Others will have to resort to maybe an old-school Digiscoping adapter?
- I will still be looking to get shorter truss tubes to try to reach prime focus with my Mod3, so I can really compare apples to apples vs. afocal.
- This scope is extremely portable for its aperture, and it's much less psychologically daunting for me to move it around compared to my extremely heavy and awkward C11. I *love* the optical quality of the C11 EdgeHD, but it's just not the scope for me at this time. Maybe if my folks move down here and get a place outside of town, I'll give it to them...
- Related to that, not having Goto, but having Telrad and Night Vision, makes for a very comfortable and fast observing experience. Now, granted, I wasn't hunting faint galaxies... I plan on adding DSCs to this in the near future, as well as a short 60mm scope to serve as wide-field and finderscope.
- As my first Dob, I found the assembly and collimation process to be very straightforward and not nearly as daunting as I think some make it out to be.
I'm really hoping that the weather holds up for our camping trip in a few weeks out to dark skies. It would be awesome to make one last run at the summertime Milky Way with this scope!!