M83 in PI and some new AO gear

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ChrisR Oz
Posts: 158
Joined: Tue Sep 28, 2021 11:03 am
Location: Melbourne

M83 in PI and some new AO gear

#1

Post by ChrisR Oz »

M83 galaxy (NGC 5236), majestic at the moment in the Southern sky, reprocessed in PixInsight using Drizzle debayer integration, Background Neutralization, Photometric Colour Calibration, stretched (but no HDR suppression), TGV noise reduction, Colour Saturation tweaked and wavelet detail enhancement (MMT). 300 x 60s subs, gain=120. Acquired using SharpCap 4.0 Pro using a Celestron EdgeHD 800 w/ 0.7x reducer, ZWO 294MC pro camera, Astronomic CLS-CCD filter, ZWO 120MM on OAG using PHD2 and AVX mount.

M83
M83
drizzle_integration_DBE_BN_PCC_stretch_TGVN_CS_MMT-50%-crop.jpg (646.21 KiB) Viewed 990 times

It is a bit mount/tracking limited. Probably need to improve my focus technique too!

Since this data was acquired, I have upgraded the system with a Starlight Xpress Active Optic (AO) plus compact filter wheel and OAG (overall optical length just 80 mm) and have seen my best tracking ever at 0.47" RMS total. Not bad on an AVX! Haven't fully explored short exposures (ZWO 120MM bin 2x2) but get good tracking results at 0.5s so far.

PHD2 using AO
PHD2 using AO
AO-PHD2-good-tracking.jpg (389.53 KiB) Viewed 990 times

It was surprisingly easy to get PHD to integrate all this and calibrate. Although, for some reason, I always need to force the calibration twice (and for each it does both AO and mount cals).

Cheers, Chris.
Celestron EdgeHD 8, reducer 0.7x, Star Sense, CGX-L mount, Focuser, CPWI; Starlight Xpress AO, OAG and Filter Wheel; ZWO 294MC/294MM Pro and 174MM mini; SharpCap Pro, PHD2, Powermate 2x, Baader Neodymium, Astronomik CLS-CCD, ZWO UV/IR, Duoband filters.
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turfpit
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Re: M83 in PI and some new AO gear

#2

Post by turfpit »

Chris

That is a really good image. A good write-up on the PI processing detail ( have just ended the 6 week trial) - thanks. Your AVX mount seems to be performing well, especially since it is carrying the 8" scope.

One question - did you use dithering during capture? I ask because this post viewtopic.php?t=5408 had 'raining noise' with 120s exposures and gain 120 using the same camera - a problem that is under investigation.

Dave
ChrisR Oz
Posts: 158
Joined: Tue Sep 28, 2021 11:03 am
Location: Melbourne

Re: M83 in PI and some new AO gear

#3

Post by ChrisR Oz »

Thanks Dave.

I’m only a few days into PI, and so this is my first go from start to finish. Much more to learn.

Yes, That is the consensus, that a 8” scope is a bit big for the AVX. I typically got more like 1.5” RMS total, after some tuning, before the AO. I thought I’d give the AO a go before considering spending much more on a good mount. I’m also hopeful that it my help with “ground seeing” effects next summer.

Yes, I always dither, triggered by SharpCap every 3-5 frames. Have tried RA-only, as advised online for the AVX. But both work, with or without DEC. Yes, I saw the post. Looks like a slow diagonal drift without dithering. Dithering also helps kill banding.

Thanks for your comments.
Cheers, Chris.
Celestron EdgeHD 8, reducer 0.7x, Star Sense, CGX-L mount, Focuser, CPWI; Starlight Xpress AO, OAG and Filter Wheel; ZWO 294MC/294MM Pro and 174MM mini; SharpCap Pro, PHD2, Powermate 2x, Baader Neodymium, Astronomik CLS-CCD, ZWO UV/IR, Duoband filters.
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turfpit
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Re: M83 in PI and some new AO gear

#4

Post by turfpit »

Chris

Thanks for the answer re dithering, I will pass that on.

With my AVX and C8 (weight 13lbs), I do mainly lunar/planetary. With 1 minute captures I don't even bother to polar align and the slight drift sort out dust motes so no flats required. For deep sky I use a Vixen 81s refractor (weight 7lbs) and can manage 300s guided (ST4) exposures without issue on the AVX.

An interesting comment about calibrating twice - I will give that a go.

PI is certainly an interesting application. I was getting to grips with masking when the trial ended. The software certainly needs a serious investment in time and effort to fully get to grips with it. The processing steps you went through make sense to me.

Dave
ChrisR Oz
Posts: 158
Joined: Tue Sep 28, 2021 11:03 am
Location: Melbourne

Re: M83 in PI and some new AO gear

#5

Post by ChrisR Oz »

Now that I'm getting used to it, it has some very nice features and is well documented (mostly, still many gaps there).

Some things are a bit odd. Even when you have stacked 300 frames (and effectively have 22 bits of precision), the output histogram of Histogram Transformation (HT) is like a comb, suggesting limited precision. Of course, that's because it's just the 16-bit histogram vector transformed, not the image histogram after transformation. Very misleading.

But aside from some quirks, it's very sound. I like the rigour of the work-flow components and processing.

Guess I'll dig deep shortly and buy it.
Cheers, Chris.
Celestron EdgeHD 8, reducer 0.7x, Star Sense, CGX-L mount, Focuser, CPWI; Starlight Xpress AO, OAG and Filter Wheel; ZWO 294MC/294MM Pro and 174MM mini; SharpCap Pro, PHD2, Powermate 2x, Baader Neodymium, Astronomik CLS-CCD, ZWO UV/IR, Duoband filters.
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