Peter and I met out at the dam last night and did some observing and saw a lot of fantastic stuff, but one of the best of the night for me was spotting three dark lanes in the Rosette Nebula.
Conditions were fairly good (SQM Meter is on my Christmas Wish List) with naked eye visibility maybe down to 4.5 to 5 near zenith, which is as good as it gets for us at Mansfield dam.
We used Peter's 16" f/ 4.5 and were doing afocal so probably working at about f/2.7 to f/2.5. I have of course studied Rosette multiple times in the 6" at f/2.8, but that scope does not have the image scale for this particular observation.
I don't know for sure if we were using 41mm Pan or 55mm Plossl, but Rosette was large and what catches the eye most is the scallops that we interpret as the petals of the rose. Peter was captivated by the dark void at the center, but I was looking more at the structure in the nebula itself.
There is a bright condensation that forms a kind of bowl shape with the top facing into the core stars. This condensation is on the same side of the nebula as the star 13 Mon. With some study, I was able to actually pick out some of the small lanes that are often shown on long exposure images. This was the first time I have seen this kind of structure in the Rosette and it adds a whole new feeling to this target. There are three very dark lanes but they are tiny at this scale. Eager to show Peter, I did not spend a lot of time on these and I had to kind of guide Peter with verbal description to them, but once he saw them and knew the scale of what he was looking for, he was able to pick out the other too.
Today when I looked at pictures, I could see that I did not follow these lanes out as far as they go, and one in particular looks to be worthy of further study.. In pictures, this one shows as a "Y" shape, and this one was the first one I came to and I think most conspicuous because it is very straight, on the end pointing into the void, and the human eye excels at picking out straight lines because this is where it sees the best contrast (and this is why I suppose optics test charts tend to use straight lines). Now, I did not take the time to study it out because the next dark land caught my attention first, but had I done so, I think it might have been possible to see the rest of the Y, though I only observed this one leg last night. The next dark nebula is not a lane, but more of a little comma shaped inclusion. It is not as long and the shape makes it appear less sharp, but it was easy to see now that my eye was looking for detail in this size range. It is short and wide, but again, if you are looking for dark nebula that has about the same size as the width of the lane in the "Y" shaped dark lane, it is easy to spot. Once I guided Peter verbally to the "Y", and told him where to look for the others, he spotted them right away.
The last one shows as much more complex in pictures, but once again, the eye does not see a jagged line as easily as a strait line, and there is only one part of this complex dark lane that stood out to me, and in eagerness to get Peter to the eyepiece, I did not spend a lot of time on this one either. Peter and I are easily distracted by shiny things, and I supposed something else caught our attention, so I did not get back to these, and I regret that, but there will be other nights.
Included is a Sky Safari capture that shows these lanes well and I am annotating them to show the ones we actually saw and what parts of them I can report as having seen with very good authority, but in the 16" f/4.5 working afocally, these are very small so be aware of that and carefully work your way though this little bowl shaped part of the nebula and my guess is that with 12 to 14", working between f/3 and f/4, with care, you should be able to pick them up, though I don't know how far you would be able to follow them, but that is why I am writing. They can be seen, and my guess is that with dark skies, a considerable amount of detail in these lanes could be presented to you.
Again, I think that that with careful study, it might be possible to follow these lanes out much further, but once you know where to look and know that the scale of these is really small, I think it is possible to see them. A good guide would be that if you can resolve some of the dark lane in the Eagle, you might be able to get these, but I think you need a larger scope working at an effective focal ratio maybe in the f/3 range is best bet, so afocal my be required.
Fantastic to see these. Don't get lost in the bigger petal scallops (easy to do) and miss these really fantastic little dark lanes!