I've been reading quite a bit, mostly here but wherever I can find some good info. I have an Explore Scientific 102mm refractor, Explore Scientific field flattener, QHY 183C imager, and Sirius mount. I bought them all used on CN. I've had some luck imaging, but my results could use improvement. Previously, I did not pay attention to the distance between the ES field flattener and the camera. I still got images, but they had lots of artifacts and I'm sure some of them were due to that mistake. I've now tried to correct for that.
My main concern is if I have everything setup correctly, especially with the field flattener. From what I can find out, the back focus of the ES field flattener is 55 mm. QHY seems to be telling me that the backfocus of the 183C is 17.5 mm. I have 38 mm of extension tubes between the flattener and the camera. There seem to still be some funny artifacts in my images. I linked a picture of my setup with the ES field flattener and extension tubes labeled.
I also linked my image of the Dumbbell Nebula. This image is a stack of 105 15s subs. I am not guiding, hence the short exposures. I used SharpCap for polar alignment until I got an "Excellent" result. I think it was within 10-20", the best I could get with the knobs on the Sirius. I stacked in Deep Sky Stacker and processed in AstroTools.
Does it look like my setup is approximately correct? The backfocus is off by 0.5 mm by my calculation, but it could be more if the measurements I have aren't precise.
Also, any obvious issues with the Dumbbell Nebula image? It looks like the colors aren't lined up - blue is shifted up/left, red is down/right. I would appreciate any feedback on equipment or the image itself.
Image link: https://imgur.com/a/omvp5yg
P.S. How does everyone get their images down to 500KB to meet the size limit for attachments?
Edit: I started writing this last night and posted this morning. I see now there was another topic posted about the same FF last night. I think we're seeing different image issues, though.
Edited by barrabclaw, 19 September 2019 - 08:43 AM.