Well, it depends what you mean by using/avoiding filters, and I suppose I should add some clarification now, after reading your reply.
My own personal take is to avoid using any filters for broadband objects, despite my LP-riddled skies. The key to overcoming LP is simply more integration, without using an "LP filter" that can block off parts of the broadband spectrum, and make color balancing difficult (or impossible). That said, there are some who use them, or some who use what might be called a "mild" LP filter that just reduces transmission in certain wavelengths, rather than fully blocks it. But I don't have or use any LP filter at all, for broadband targets.
I do use filters for emission targets often. For my DSLR right now, that is an L-eNhance. I also just started using a single wavelength narrowband SII filter, even with DSLR (being the heathen that I am
).A UV-IR cut filter, however, is another issue. Those are not LP filters, really. Instead, they block the UV and IR extremes of the spectrum. This is in fact something you want to have, if your camera doesn't have this built in. Otherwise you can end up with not only color balance problems, but bloating (particularly stars) and potentially focus issues, due to the wavelengths involved. For AP,, absent special circumstances, we are pretty much interested in the 400 to 700nm wavelengths, regardless of whether one is doing broadband or narrowband.
My full spectrum modded D5300 requires a UV-IR cut filter, otherwise I will be capturing some sub-400nm UV, and some past-700nm IR. For this, I picked up a relatively cheap SVBony 2" UV-IR cut. There are many options and manufacturers of these, probably all of varying quality and anti-reflective coatings. But UV-IR cuts are generally inexpensive regardless. They are also often the exact same thing as an L (Luminance) filter. But you can check the specs and graphs for that.
Your 294MC Pro does not have a built in UV-IR cut, I believe, only AR coatings on the protective glass. As such, absent a UV-IR cut filter, you will be capturing some amount of UV and IR outside of 400-700nm. You do not want that. I am unsure of the UV and IR transmissivity and responsiveness compared to my full spectrum DSLR, but it is the same general concept.
As to other filters, such as nebula/emission filters, many of them have UV-IR cut included by their nature. But not all, so you do have to check. The L-eNhance, which I use, passes Ha in the red, and OIII+Hb in the green and blue, blocking everything else, including UV-IR.
Now the next issue. In addition to Carles tips, note that the 294MC is, as noted, finicky. Generally speaking, for proper calibration, long exposure flats (maybe 2-3 seconds or more) and matching dark flats, rather than using bias, are recommended. That said, I have seen several datasets where calibration seemed to work okay even when the dark flats were taken outside the recommended exposures. There's really no way to tell other than analyzing the linear histogram of the raw FITS to see what was captured and if the calibration will work right.
This is probably one of the more in-depth descriptions of 294MC calibration on CN, done in the expert forum. So it can get pretty dense. But you can just skim it and jump to the summaries and conclusions, if so interested. https://www.cloudynights.com/topic/6363 ... -opinions/
I do not know if ZWO has made any firmware or driver changes that address the peculiar exposure vs ADU levels oddities of the 294s.
Anyway, might be something worth trying though and seeing how your rig responds, or at least checking all your histograms to make sure nothing seems like it might be in the wrong place, and could lead to miscalibration.
Hope all of that is helpful!
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