RCC - What's going on here with my image of M81

Your flat correction is not good.  There are uncorrected dust mote all over the place.   Go back and blink through your calibrated data and it will jump right out.  Next you have to fix the calibration but I can’t say much about how to do that without more information.

Good luck…

John

Wow, that's an amazing artifact!

I have almost the exact same optical train (no additional FR in mine, just the built in flattener).

Looks like maybe dust on two surfaces. The smaller donuts are probably dust on the camera's glass window. The bigger ones may be on the filter or FR a few millimeters in front. None are on the sensor itself…those are generally smaller, dark, and ugly. They don't defocus to the shape of the primary.

Dark donuts are new specks not recorded in the flat. Light donuts are imaged in your flat, but the specks that caused the shadows are gone. And the donut with the drop shadow in the upper left is a speck that has shifted slightly.

But I have no idea what the oval white cloud is…unless M81 is about to absorb another galaxy!

Did you have any dew heaters running? If they were off, including the window heater on the 2600, maybe condensation exaggerated things a bit. The whole image appears to have smear over it in addition to the donuts.

Otherwise, nice shot of M81! I bet a careful cleaning and new cal frames will make the target look terrific!

Dave Rust:
Wow, that's an amazing artifact!

I have almost the exact same optical train (no additional FR in mine, just the built in flattener).

Did you have any dew heaters running? If they were off, including the window heater on the 2600, maybe condensation exaggerated things a bit. The whole image appears to have smear over it in addition to the donuts.

Otherwise, nice shot of M81! I bet a careful cleaning and new cal frames will make the target look terrific!

Dave,

I'm running the Celestron dew heater ring on my C9.25. I connect it to one of my ASIAIR 12v power outs, but I have no way to control it, so maybe it's running hot. Could that be a source of some of the artifacts? I also have the ASI2600 anti-dew power on.

One other issue could be the IR Cut filter. Do I need one for galaxies in my light-polluted skies with the ASI2600? I read somewhere that the protective glass on the camera is a cut filter.

Glenn

I think the camera window is also an IR cut filter. I use a pollution filter (HEUIB-II) and a Ha-OIII-Sa filter (Triad Ultra) with good results…and IR has not been an issue with those, either.

So, unless there is light leakage, say, from a filter drawer, and/or condensation (which I've not seen yet on a filter), I don't think filters would cause what you are seeing.

I also ran the ring off ASI. I did not see any abberation from using full-time power. But my battery bank sure noticed! I did later get a lower cost pulse-width power controller, which helped.  But, to make sure, I now run an extension cord when I want a full 8 hours out of the rig.

Glenn,

I have had some donuts show up like that before, working through my flats process. It was nowhere near this many, but I was able to "fix" the image by running Starnet/StarXTerminator, then using PixInsight Clone Stamp to remove the artifacts before recombining. 

-Chris

Glenn Silverman:
I have tried to clean the imaging train and it looks clear enough, but getting all the smudges out can be a problem, especially on the C9.25 collector plate.

Glenn,
The corrector plate is at the system stop so the condition of the corrector will not produce dust motes.  Neither will dust on the primary or the secondary mirrors.  Dirt or other contamination on the field lenses may cause a problem but most motes will come from dirt (or surface defects) on any filters, reducer components (if you have one) and/or the sensor window.  Those need to be kept extremely clean and that's where you should be the most OCD in your cleaning efforts.  

Jay Hovnanian:
4.  Adjust the light panel intensity such that a test shot of 3 or 5 seconds results in a median histogram value (its technical name escapes me)
     of right around 20,000.  Once you are there, set your Autorun Flats to the 3 or 5 seconds and take thirty (30) Flat frames.

Jay,
There is no need to take so many flats.  Properly exposed, Flats have a very high SNR so their influence on the statistics of the final image is quite small.  Taking more flats than necessary won't hurt anything but you really don't need more than around 8-16 to make a good flat master.  The reason that's relevant is that for some EL flat panels, it can be hard to properly expose NB flats in the red (e.g. Ha and SII) without using pretty long exposures (sometimes many minutes), which can be pretty time consuming as you run through all of your filters.

John

Hi Glen,
You mentioned, that you have to crop the Image because of the edges. Are the edges to bright or to dark?
this could point to problems with the darks. Older darks or darks with different Gain/Offset can cause problems.
the other question are the flats from the same night?

To troubleshoot i would process a subset of the light frames to speed up processing
1. no bias, no darks, no dark flats just the lights and the same for the flats the compare if the dust is on the same spot and size
2. lights + flats (no bias, no darks, no dark flats) is the result free of dust spots?
3. the same only with bias
4. the same only with darks

CS
Detlef

Most dust donuts are undercorrected but others are overcorrected. This indicates light leaking inside the dark or bias subs.