50.2 ± 5.5 MLy (for all 3 prominent galaxies)

It was a real struggle to get this image as clouds played havoc with it. Hence, it took several sessions to get enough data. I was also trying for M83 as a second target on the nights I collected this, and between clouds killing sessions and a mountain in the way I still don’t have anything for that. In processing this image, I tried both my usual workflow, in which I treat the L and the RGB separately, and also combining LRGB and using synthetic luminance from the RGB, processing the whole thing at once. I think my usual workflow gave better results, at least this time, as I tend to process L for sharpness and RGB more for smoothness. There were pretty significant background gradients that my flats did not fix and eventually I ended up using GradientXTerminator for them. The result is a much better image than my previous attempts on these targets (including the fact that I got all of them in one frame this time, which wasn’t possible with my small-chip DSI IIc camera). I notice that the core of NGC 4254 came out looking slightly green, which doesn’t seem quite correct but it’s what my data yielded so I’m reluctant to mess with it. The star colors look reasonable and changing the color balance changes that. I’m never sure about how accurate my colors are (I usually go with what StarTools’ color module gives), but one thing I’m fairly confident of is that the 3 most prominent galaxies in this image have distinctly different colors. I’m guessing that might reflect different average ages of their stellar populations, or perhaps differences in dust content and the accompanying scattering. I didn’t realize NGC 4254 is in the Messier Catalog (M99) until I was looking up distances in Wikipedia!

Date: 18-11 Apr 2020
Subject: NGC 4254, 4298, and 4302
Scope: AT8IN+High Point Scientific Coma Corrector
Filters: ZWO 31 mm diameter unmounted L, R, G, B
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + ASI120MM-mini +PHD 2.6.7 (Win 10 ASCOM)
Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21
Acquisition: Sequence Generator Pro 3.1.0.457
Exposure: 60x180 L, 20x180 R, 22x180 G, 24x180 B
Stacking: Deep Sky Stacker 4.2.3 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5
Processing: StarTools 1.6.392 beta: Software binned L 2x2, cropped, wiped, developed, HDR (reveal core), deconvoluted, untrack denoised (grain equalization). Combined R, G, & B in StarTools, accounting for the differences in integration. Software binned 2x2, cropped, wiped, developed, HDR (reveal all), color, untrack denoised (grain removal). Applied L to color in Photoshop. A little bit of levels, one round of deep space noise reduction. AstroFrame.