Conditions were much less than optimal for this image; intermittent high clouds mixed with thicker ones. However, it’s the best I’ve had in weeks so I decided to give it a try. On top of the weather problems, my home-brew stepper-based focuser is on the fritz (broken and/or shorted wires in the connector, for starters) so the automated focusing was working only intermittently if at all. I think I also found the source of my optical distortion with the AT8IN. The focuser is not set with the correct tension, and therefore sags pretty badly. I did not have high hopes for this image, but I am learning a little better how to handle my new camera. For this image, after seeing results others have obtained using the zero gain setting (maximum dynamic range), I decided to give that a try. I also saw some Cloudy Nights posts (by GeneralT001) listing optimum background levels to aim for at different gain settings. According to those numbers I’ve been WAY overexposing. I never thought it was possible to overexpose a deep sky astrophoto, but decided to try to hit the suggested optimum exposures, which are much shorter than I’m used to. This image is the result, and to my surprise I think it turned out better than my previous best of M51, which is one of my all-time favorite targets (at least in terms of how frequently I attempt it). Even with what seem to me to be very short exposures given the low gain setting, the tidal tails show up and the detail is better than before, especially in the pure luminance data (I lost a little when color was added). The color balance feels better in this image, although there may still be too much green. I wonder how this would look under good conditions.

Date: 5 Apr 2017

Subject: M51, Whirlpool Galaxy

Scope: AT8IN + High Point Scientific coma corrector

Filters: ZWO 31 mm diameter unmounted L, R, G, B

Mount: EQ-6 (EQMOD)+PEC

Guiding: Orion Thin Off-axis Guider + DSI +PHD 2.6.3.2 (Win 10 ASCOM)

Camera: ASI1600MM-Cool, -20 °C, Gain 0 Offset 10

Acquisition: Sequence Generator Pro 2.6.0.21

Exposure: 59x120 L, 20x180 R, 20x180 G, 22x180 B

Stacking: Neb 4.1.5, flats & darks, trans+rot align, Nebulosity 1.5σ stack and align.

Processing: StarTools 1.4.327. Aggressively stretched and deconvoluted the luminance. Combined RGB in Neb 4 and stretched and attempted to color balance and correct in StarTools. Layered luminance over RGB in Photoshop CC 2014, boosted the saturation a little, and used Carboni’s Astronomy Tools deep space noise reduction, topped off with AstroFrame.