Nice clear night and the crescent Moon set early. I wanted to give the SVBONY SV193 0.8 Focal Reducer I have for the SV503 a try in the AT66ED. Wanted to see if I could get focus and if it helped flatten the field any. With the 0.8 Focal Reducer the AT66ED focal length becomes 320mm making it an f/4.8 scope. I focused on the IC 1805 and the Heart Nebula so I would have some other data from a recent session to compare it to.

I did have to tinker with the spacing between the focal reducer and the scope. There was way too much and I did not have enough inward focus. I removed a couple of spacer and was able to get focus fairly quickly. The field does appear to be much flatter there is some elongation of stars in the lower right and left of images, but no where near what it was. I may have some tilt in the sensor or my spacing between the focal reducer and the sensor may need some adjusting.

Spacing to the camera sensor should be right at 55mm. There is the 6.5mm in the camera body, then the 21mm of the filter drawer, then an 11mm spacer, and finally a 16.5mm spacer = 55mm.

Primary (Imaging)	Secondary (Guiding)
Scope: Astro-Tech AT66ED with .8 Focal Reducer (320mm – F/4.8) Reducer/Flattener: None Filter: SVBONY SV240 Multi-Narrowband Camera: ZWO ASI294 MC Pro, Cooled to -10 C Focuser: Gemini Autostar Focuser Mount: Sky Watcher EQ6-R Pro	Scope: SVBONY SV165 30mm F/4 Guide Scope Camera: Orion Star Shooter Autoguider (OSSAG)
Telescope Control, Image Acquisition, and Image Processing Software
Equipment Control and Imaging Software: NINA/PHD2/ASCOM on a Mini-PC Processing Software: GraXpert, Siril astronomical image processing tool, Siril’s Interactive Companion (Sirilic)

I had to rebalance things since I removed from spacers. When I did I unplugged the camera and forgot to turn the cooler back on. I was a little later getting started waiting for the camera to cool back down.

The Heart Nebula or Sharpless 2-190 is a large emission nebula in the constellation of Cassiopeia.

Here are the results from 40 x 180 seconds at gain 121, offset 30, and bin 2×2. Stacked with Sirilic, then cropped, background extraction, and denoising with GraXpert, and final processing in Siril.

I did not bring up the saturation as much as I did on the images from the previous session. Some neat details in the shadows of some of the clouds. Stars are a bit bloated, but at least they are fairly round across the field of view.

Will probably have one more session on the Heart Nebula to compare the SV240 multi-narrowband filter results with the ZWO Duo-band filter results. Stay tuned.