Dan, one thing to note. You are in a yellow zone. That gives you a BIG advantage in using an OSC camera. Yellow zones are pretty good...LP is more balanced with light from space and airglow, so it isn't overpowering. Your Orion nebula image demonstrates that...it's low noise, very clean with minimal gradients. My dark site is in a green zone near the border of a yellow zone, and sometimes sky brightness goes below 20.8mag/sq" (definite yellow zone)...and the results are still orders of (stellar) magnitude better than my red/white zone back yard (literally.)
For people in a yellow zone, and certainly green or darker, I think OSC cameras work great. They can definitely support a simpler workflow. I think people who live in an orange, red, pink or white zone really need to pause before they pull the trigger on an OSC camera, because LRGB, even if the equipment is a little more to learn up front, is going to be capable of delivering usable results without all the frustrations with nasty gradients and the like that you would have with OSC. Not everyone is lucky enough to have the kind of darker skies that a yellow zone offers, and for so many living in a red zone (most suburbanites), OSC data can be a frustrating mess more often than not.
Jon, won't the L filter still let in light pollution? So is it better to do RGB and synthetic L when imaging from a red zone? Or use an LPS filter for the luminance channel?
I've been going back and forth deciding between an OSC and mono My dark site is bortle 4 and local site is a red zone. The 071 is very tempting!
Yes L will let in LP. No, I don't believe synthetic L is going to improve anything. The thing about a synthetic L is that it LITERALLY ADDS ZERO INFORMATION to your final image. You may be able to do certain things with processing on a synthetic lum that are easier than doing them on the separate or combined RGB, however a synthetic L is derived from the RGB. It won't add any more SNR to your image. I have heard from a lot of people that synthetic L works great, however theoretically, mathematically and in my experience with DSLRs in practice, I have never found that they ever actually improve SNR. I often preferred separating out a synthlum with my 5D III just to simplify processing, and some things (like deconvolution) always worked properly on the synthetic lum, but rarely on the RGB.
If you truly want to improve your SNR, then you must use either an L filter, or an LP filter in place of the L filter (not for color, but for LP protected luminance). Only ADDTIONAL frames from a separate filter will actually give you the true SNR benefit of LRGB imaging. Conversely, you can simply skip L alltogether, and put a lot more time into the RGB filters. If you were aiming for say 6 hours of integration total, with 4 L and 2 of combined RGB, there is no reason you couldn't drop the L and just put 2 hours each into RGB. You would benefit from the couple of small gaps at the ends and between the RGB filters that way, which would block out some LP. But, for the most part, all that really does is block out the primary sodium vapor emission lines. It actually doesn't block out any other LP lines. IMO, you would still be far better off using an L filter, and just acquiring a lot of L data.
Here is an example (I may have posted this before, but here it is again). These two images of Andromeda are from my back yard, a red/white zone in a suburban area. The first image is 7.2 hours of 5D III OSC data during October and November from a couple years back:
The second image here is 3.4 hours with an ASI1600 and LRGB, with 1h56m of L, 20m of B, 30m of G and 40m of R from a couple months ago:
This is the same heavy LP. Less than half the total integration with the mono, and it looks significantly better. I added 1h24m Ha data to the new image as well, and enhanced the color a bit more:
The Ha data was a bit sparse, and really needs to be 3-4 hours of integration, so it pulled down the SNR of the final image a bit. However, it still looks considerably better than the OSC image.
Without the L data for my new image, I'd have had to put more time into each of the other filters. Since they are each only acquiring a third or less the light, I would have needed a lot more integration to get the same final SNR.
I've thought about picking up an IDAS LPS-D1 1.25" filter to use in place of my L. I haven't done that yet as it doesn't seem to matter what size IDAS filter you buy, they all cost the same ($190), which I find to be ridiculous, and I'm not really sure how much of an improvement it will really offer in the end. I have larger IDAS filters, and I keep meaning to give them a try before I buy another one. I always felt the color ended up a bit too blue-green with the IDAS LPS-P2, so I stopped using it on my OSC data. However, used as an L filter, it might be perfectly fine, and could provide higher contrast data for a luminance channel. I'd probably need to double my integration time with it, as the IDAS filters in my experience block out about a stops worth of light. So, my 3.4h integration would become a 5.4h integration.
Just to be clear to everyone. I am recommending mono if you live in a light polluted area. I think the ASI071 will be an awesome camera with a relatively large sensor, IF YOU LIVE UNDER DARK SKIES. OSC is great with dark skies, where LP can't decimate your SNR and spew colorful crap all over your data. I stopped using OSC cameras in my back yard in February 2015, as after seeing what just 2-3 hours could do at a dark site, spending 11, 12, 15, 18 hours in my back yard to get WORSE results just wasn't worth it anymore.
If you live in a yellow zone or darker, and want the largest frame in a cooled astro camera that you can currently get, I say look no further than the ASI071.
If you live in an orange or brighter zone, particularly red/pink/white, skip the OSC. Even with added mechanical complexity, mono+LRGB is vastly superior. Despite the fact that an L filter lets in more LP.