Cygnus Loop with faults

[DaveS]

An hour's worth of HII data in 2 min subs with the Star Adventurer and 180 f/3.4 Apo-Telyte-R and ASI183. Filter was the cheapo Baader 7nm rather than the Astrodon 3nm that I would have prefered as that would have meant dismantling another rig. Images on holiday in a Bortle 3/4 area of Dorset, near where where I'll be moving to.

Sigma Add stacking in AA5 with Darks and Bias, then several rounds of Histogram Stretch. No gradient removal.

Posting the whole uncropped image to show the faults, tracking errors (RA only I think, so guidable) and still a huge amp-glow despite the Dark frames. A meridian-flip can get rid of this in Sigma stacking.

Closer attention to the framing (I was in a hurry, and had already made two adjustments) would have got more of the Western Veil.

[Rodd]

I have never seen amp glow that bad.  Almost looks like a big star just off the FOV/  How was your focus?  You have your RA axis up-down in this image correct?--slight elongation--but I don't think an image ruiner

Rodd

[DaveS]

I agree that the amp glow is horrendous, and that's *with* dark frames.

I wonder if this is usual with the ASI 183 MMC? Connection was through USB3.

I wonder if @FLO would know?

[Allinthehead]

Hi Dave. It might be worth having a read of this. https://www.cloudynights.com/topic/603693-asiqhy-183-mono-release-thread/ and this https://www.cloudynights.com/topic/604214-new-zwo-asi-183-mono-uncorrectable-amp-glow/

[DaveS]

Thanks for the links Richard, much reading to do, but sounds like I may have to longer darks than my lights.

CMOS cameras look to be more tricky to use than CCD.

[Allinthehead]

41 minutes ago, DaveS said:

CMOS cameras look to be more tricky to use than CCD.

I have two and no trouble like this. Although once i had an Oiii stack that couldn't be calibrated but it never happened again so i put it down to something stupid that i did.

[DaveS]

After reading the CN threads I'm trying some 4 min Dark frames to see if those will clear the problem. I've put the camera in the 'fridge so the cooler can reach set-point.

Also wondering if Bias frames are the trouble?

[DaveS]

OK, I tried 4 min Darks, but that left a dark patch where the amp-glow had been.

I then tried stacking using just the dark-frames, as I had read that Bias could make matters worse with CMOS, and this is the result.

It's better I think, though there is still a dark area where the amp-glow had been, possibly as the temp wasn't quite as low when I did the darks. More investigation required I think.

[ollypenrice]

If the worst came to the worst you could stack twice, once to get an under corrected image and once to get an over-corrected one. You could then average them till you ended up with a neutral blend. In Astro Art this would be dead easy because you'd just open both images, go to Arithmetic-Average and adjust a slider till you got the perfect blend visible in real time as a screen stretch.

Solving the problem at source would be better but this method might help.

Olly

[DaveS]

Thanks Olly, yes that's my next point of attack though of course, as you say, solving the problem at source will be best.

[DaveS]

Well, I had a first go at averaging a stack with dark and bias, and another stack with dark only

Unfortunately there is now a dark annulus that I can't get rid of in averaging. More work / research needed. Maybe I've stretched the data beyond its limits.

[Hallingskies]

If it was me I’d just crop it.  You otherwise have a nice image...?

[Rodd]

I was advised by ASI 1600 users (cmos) to forgo the use of bias frames.  I was having a tough time calibrating at first.  In PI what worked was not using bias frames (darks, flats and flat darks), and making sure to leave the box for scaling darks unchecked in the BPP script.  (that was the real thing--bias were dropped and I have not used them since--but I think it was not scaling the darks.)  The darks should be the same temp and time as the exposures.  But that just might be an idiosyncrasy with PI.  Not sure.  I would check the dark frames to make sure the cooling hadn't been deactivated--that happened to me once.  Confounded me until I discovered the dark frames with 20 degrees warmer than the lights.  Still don't know how the cooling got switched off.

Rodd

[DaveS]

I need to think about this.

The darks I took were through USB2, whereas the coresponding lights were through USB3, so I'll get some new ones.

I really don't want to waste precious imaging time getting darks, and I really don't see the point provided they're taken at the same temp and through the same data path.

[DaveS]

Well I tried Darks through the USB3 connection and got the same dark halo around the amp-glow. Bother. I really think this chip is unusable without cropping, and it's small as it is.

Here is the latest and final (?) version with the USB3 dark frames, plus a few rounds of histogram stretch. This is as far as I could take the data without getting combing in the histogram.

The only time I've been able to get rid of the amp-glow is when I had a meridian flip in my run of subs and Sigma stacking treated it as an artifact.

[Allinthehead]

On 25/07/2018 at 12:24, DaveS said:

Bother. I really think this chip is unusable without cropping, and it's small as it is

Would you consider returning it? If i couldn't remove the amp glow then that's exactly what i'd do. Save up the pennies for a 1600.

[DaveS]

I already have a 1600, need to update my sig.

Bought the 183 because the 2.4 micron pixels are a good match for my 80mm f/4.4. Also a good match for thr 180 Leitz apo.

[MarsG76]

Nice and deep result.. sooo many stars....