Rick Veregin:
u make some very good points, Jon, and I do apologize for missing your point on color. There is no question that LP filters do make it more challenging to get the right color, some filters more than others. Just as there is no question a dark site is the best option if that is in your DNA.
I live in Bortle 8/9 (Red/White zone, or 17.8-18.5mag/sq") as well. I've been imaging here since 2013, and I've used plenty of LP filters (still have em, too.)
I in all honesty, cannot say that the LP filters made anything better. I don't know that they really made anything easier. Every single LP filter I have ever used saps the color in such ways that I was never able to get a good result that I was truly satisfied with. The can be a way to get by when you have absolutely no other options, IF you are mostly interested in emission nebula. It may be a matter of taste, but I've never liked how my images looked when using LP filters. I ended up liking just doing broadband imaging unfiltered, but then, I was also always one to stick with my targets for as long as possible, and I would get 10 hours or more on each.
Getting lots of data...tens of hours, with or without LP filters. Well for one, there was NEVER enough data. You could get hundreds of hours from Bortle 8, and it would never be enough. But its not just about the amount of object signal you ultimately have, tons of heavily polluted data has its own problems. I threw around 40 hours once at an image of the Pleiades... And it was barely any better than 10 hours, and with so much data across so many nights, the LP "gradients" where in such a disastrous state that extracting the resulting mess of criss-crossing gradients of different intensities, shapes and colors that spanned months of different skies was more effort than it was worth. The problems I faced with pollutant signals shifted a bit, from right in the core of Pleiades, to all the softer structures interspersed among the primary stars, as well as the faint structures in the sky around them... Actually, I do remember the core still being a challenge, as properly neutraizing the LP gradients right in the core was practically impossible because of how much nebulous structure there was there. In the end, either I left some of the LP in, or ended up with a overtly dark, nearly black core once all the LP was extracted. It was a horrible mess, and I don't think I acquired quite that much data on any other object from my light polluted back yard again.
Then....I visited a dark site, and had my first taste of what it was like to simply NOT HAVE the LP, at all. There is nothing like a dark site, which need not be hundreds of miles and countless hours away. It also doesn't need to be all that complicated from a setup standpoint either. Once you move away from polluted skies, OSC will perform remarkably well, if you want an easier time of it. There are also things you can do (speaking from experience, as I spent years driving out to dark sites) to make setup easier. One, you can keep your mount stuff largely assembled, so there are only a couple of things to do to get the mount set up. Two, you can configure your telescope such that pretty much everything to make your system work, is on the scope. Acquisition PC (i.e. NUC), USB hub, power distribution, and necessary cabling, as well as the scope, focuser, filter wheel (if applicable), and anything else, including the necessary dovetail, can all be configured as a single unit that you keep assembled at all times. You then just have to drop the pre-assembled scope setup onto your mount when that's set up, plug a couple of cables in (data and power only, usually), and you are just about ready. Polar align, and you can go. Maybe you need to temporarily plug a portable monitor into your NUC to get things going, or maybe you can do it with your mobile wifi access point and a table or laptop. Regardless, once you get that figured out, its generally just a matter of kicking off your imaging sequence. With software as it is today, you can pre-configure that at home before you leave, and once you start the acquisition sequence it should take care of all the rest for you, right?
Imaging at a dark site doesn't need to be hard or complicated. A SINGLE night at a dark site, with a couple/few hours on each object, could be worth MONTHS of many nights from a heavily polluted back yard site. Especially during the months with longer nights. If you put 3 hours into each target, you could potentially image say 3-5 objects each night, depending on whether its early or late spring/fall or winter. Even on a summer night, you could still potentially image two targets in a single night. Those two targets would have a quality of data unparalleled in comparison to dozens of nights in a light polluted back yard. So, is dark site imaging really more complicated? You could potentially visit your dark site, say, once or twice a month, and end up with high quality data on far more targets than a year or more in a light polluted back yard.
And what if your dark site was just 30 minutes way, instead of 6-8 hours (or even a day+) drive away (like a Bortle blue, gray or black site might be)?
Now, there is always that weather risk. Can't do much about that, but...if the risk is to drive 30 minutes to a nearby imaging dark site, and find an hour in that its gonna be a bust due to the weather, well...that isn't so bad. I have some other dark sites I don't use anymore (found early on in my foray into dark site imaging) that are MUCH farther away (the nearest of which is 80+ minutes out, the farthest several hours) where bad weather would be a raw deal indeed. The imaging site I use most often, however, is just 35 minutes away at the posted speed limits. So if a night ends up a bust (and many have over the years), its not as big a deal. Its a bit annoying to think its gonna be clear, set up, and actually get the sequences going...THEN have weather roll in. You can then certainly waste a couple of hours. Still...a SINGLE night out there, is SO much more productive than months in my back yard...I always felt it was worth the effort.
If you only image with really heavy gear, then that can indeed hamper getting going at a dark site. I wouldn't necessarily recommend lugging around say a 14" EdgeHD or something like that. If you wanted to benefit from mobile dark site imaging, then something smaller, and 8" or 9.25" EdgeHD instead? Or maybe a newt? Something lighter weight that can be set up and torn down easier. You can do higher resolution imaging from a dark site, if you really want to. If the only way to acquire the kind of images you like is with LARGE and HEAVY gear, though, then no, mobile dark site imaging is probably not for you.
A permanent dark site observatory probably is, though. (Yes, I am well aware of how expensive that can be, and that its a hurdle, and that it won't work for everyone.)
I would challenge everyone who thinks they couldn't image at a dark site or that it wouldn't be as useful as a polluted back yard sky, to give it a try. At least if they have gear that is portable enough. Use the VIIRS mapping data from lightpollutionmap.info, find a CLOSE dark site that even just "might" work, and give it a try. Give it a few tries. I would be willing o bet that once everyone got the hang of how to get out there, set up, and get going quickly, that their dark site imaging trips would be VASTLY more productive than any of their time imaging from home. Which could then mean that, a once-a-month well-planned trip to the dark site (when you know with high confidence what the weather and wind will be) could be completely transformative to their imaging overall.
