This is first light for using my new ASI120MM-mini guide camera. In the process of setting it up, I attempted to correct the vignetting issues I’ve experienced for some time. I actually took some luminance subs of this target with the old setup but the problems were so severe (and the flats were so poorly matched) that I threw out all of them. I flipped the filter wheel to put the filters a little closer to the camera, reoriented the OAG prism so it is on the short side of the main imaging sensor, and pulled the prism out to minimize its shadow on the sensor. I then carefully readjusted the distance from the prism to the guide sensor to get better focus. As a result I have less corner vignetting and a lot less shadow from the OAG prism. It was a bit of a struggle getting the new camera functioning correctly with SGP and PHD2; the connection to one or both ASI cameras kept dropping randomly. Experimenting a bit, I finally settled on cabling the 120MM-mini into the 1600MM-cool’s USB port, then brought the USB3 cable from the 1600MM-cool back to the USB3 hub, saving one cable. After a bit of reading, I came across a suggestion to use the ASI120MM-mini in 8-bit rather than 16-bit mode, which helped the stability a lot. I still had a session hang even after doing this, so I also suspended guiding during image downloads and limited the USB speed to “45.” I got a complete session last night, so I hope I’ve finally got everything sorted out. This guiding setup feels far more sensitive than what I had before using the DSI IIc guide camera; I’ve had decent guide stars for every target I’ve tried with it. The image was far easier to process because of greatly reduced vignetting and better flats, and overall I am pleased with the result. It is far better than my last previous attempt on this target, but it ought to be given that the last time I attempted it was 6 years ago!

Date: 1-4 May 2019
Subject: The Chain of Markarian, centered on The Eyes
Scope: AT8IN+High Point Scientific Coma Corrector
Filters: ZWO 31 mm diameter unmounted 7 nm L, R, G, B
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + ASI120MM-mini +PHD 2.6.5dev6 (Win 10 ASCOM)
Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21
Acquisition: Sequence Generator Pro 3.0.3.170
Exposure: 70x180 L, 20x180 R, 32x180 G, 28x180 B
Stacking: Deep Sky Stacker 4.1.1 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5.
Processing: StarTools 1.4.341: Cropped, wiped, developed, HDR optimized, deconvoluted, and untrack denoised the L data. Combined RGB in StarTools, then cropped, wiped, developed, and used the color module on the RGB data, with the default setup looking good to me. Untrack denoised. Combined L with RGB, performed deep space noise reduction, and made a slight levels adjustment. AstroFrame.