Centaurus A before and after AO

Anything that doesn't fit into any of the other forums
Post Reply
ChrisR Oz
Posts: 119
Joined: Tue Sep 28, 2021 11:03 am
Location: Melbourne

Centaurus A before and after AO

#1

Post by ChrisR Oz »

It figures that after I installed the Starlight Xpress Active Optic (AO) that Melbourne winter weather would roll in. Sure enough, last clear night was May 24. But with luck got a brief clear window last night. All worked very well with guiding at 0.5" to 0.6" total RMS using 0.5s exposure on the 120MM guide camera all orchestrated by PHD2. Of course the clouds appeared, and I only ended up with 19 minutes on Centaurus A. All packed up by 7:20 pm - what an anticlimax.

But it gave this comparison between Centaurus A using PHD2 and a more typical 2s exposure (left) and using the AO at 0.5s exposure (right). The FWHM cut-off was 4.7 pixels before and 2.6 pixels (1.68") with the AO. So although the final image with AO just used 16 frames (16 x 60s), it shows some great detail. Thought this comparison might be of interest ...

Before (Left) and after (right) SX AO
Before (Left) and after (right) SX AO
CentaurusA-with-AO.jpg (740.94 KiB) Viewed 194 times

Left used about 60 minutes x 60s (ZWO 294MC Pro at gain=120), while right used AO and 16 x 60s processed in PixInsight. The AO manages to tame the wild AVX mount.
Cheers, Chris.
Celestron EdgeHD 8, reducer 0.7x, Star Sense, AVX mount and Focuser, CPWI, Starlight Xpress AO, OAG and Filter Wheel, ZWO ASI 294MC Pro and 120MM mini, SharpCap Pro, PHD2, Powermate 2x, Baader Moon & Skyglow, Astronomik CLS-CCD, ZWO Duoband filters.
User avatar
admin
Site Admin
Posts: 9137
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Centaurus A before and after AO

#2

Post by admin »

Hi Chris,

well that's a pretty impressive improvement in image quality. You must be very pleased (apart from with the weather...) :)

cheers,

Robin
ChrisR Oz
Posts: 119
Joined: Tue Sep 28, 2021 11:03 am
Location: Melbourne

Re: Centaurus A before and after AO

#3

Post by ChrisR Oz »

Hi Robin,

Yes, it has worKed out well. It even puts up a good fight against a light breeze. I’m also looking forward to see how it might fare against thermal effects close to the ground with hot surfaces in summer. For that I’ll need to work down in exposure. I have done tests down to 0.1s. But success will depend on available guide stars. My next purchase will be a larger guide camera with somewhat larger pixels for more sensitivity.

Cheers, Chris.
Celestron EdgeHD 8, reducer 0.7x, Star Sense, AVX mount and Focuser, CPWI, Starlight Xpress AO, OAG and Filter Wheel, ZWO ASI 294MC Pro and 120MM mini, SharpCap Pro, PHD2, Powermate 2x, Baader Moon & Skyglow, Astronomik CLS-CCD, ZWO Duoband filters.
timh
Posts: 377
Joined: Mon Aug 26, 2019 5:50 pm

Re: Centaurus A before and after AO

#4

Post by timh »

Hi Chris,

That looks really interesting ! So the AO guide camera system works via an OAG and corrects more quickly and/or accurately than conventionally via PHD2? You described it as taming the mount. Could you enlarge as bit on exactly what the mount problems were that it was taming? My mount currently appears to have a problem with short sharp oscillations in RA --about 2 arcsec at a frequency of once per second. It causes star shape distortion at high resolution. Just wondering if the Starlight AO system could be a potential solution here also?
Anyway - an excellent-looking second image

Tim
ChrisR Oz
Posts: 119
Joined: Tue Sep 28, 2021 11:03 am
Location: Melbourne

Re: Centaurus A before and after AO

#5

Post by ChrisR Oz »

Hi Tim,

Thanks. The SX AO integrates into PHD2 well, so for the most part, PHD nudges the AO (tip-tilt glass plate) to correct and centre a guide star. When the AO gets somewhat off centre, then PHD nudges the mount. It continues driving the AO, which helps correct for how the mount responds to a nudge. And even if the star movement is due to a light breeze catching the dew shield, it will correct that too.

The AVX is renowned for somewhat “wobbly” guiding and plenty of DEC backlash. I did tune it, which helped RA a factor of 2. But DEC remains with the best part of 1000 ms of backlash.

I was expecting to be tracking “seeing”, which would be pointless. But even down to 0.5s, it seems to be correcting genuine misalignment. I first started using 0.5s exposure before the AO, after some recommendations specific to the AVX on Cloudy Nights. That and “Periodic PEC” algorithm for RA helped quite a bit. But the AO has reduced RA RMS further by nearly a factor of 3. I’m seeing RA RMS around 0.3” a lot of the time.

Yes, I think the AO could help with your RA too. I chose the SX AO because it is easily integrated into PHD2, and the SX AO, OAG + filter wheel combo is very compact, only about 80 mm total “optical” length, so fits in my restricted available back-focus (105 mm w/ reducer). The SX OAG prism mirror is a bit larger than my ZWO at about 10 x 8 mm, if I recall correctly, which means I can upgrade to a ZWO 174mm mini sometime soon. This will also help sensitivity as it has slightly larger pixels and bin2 would be about right.

Cheers, Chris.
Celestron EdgeHD 8, reducer 0.7x, Star Sense, AVX mount and Focuser, CPWI, Starlight Xpress AO, OAG and Filter Wheel, ZWO ASI 294MC Pro and 120MM mini, SharpCap Pro, PHD2, Powermate 2x, Baader Moon & Skyglow, Astronomik CLS-CCD, ZWO Duoband filters.
rockenrock
Posts: 23
Joined: Tue May 03, 2022 12:53 am

Re: Centaurus A before and after AO

#6

Post by rockenrock »

Hi Chris,
The detail in the galaxy, and the stars are both really improved. Very nice capture, and have fun with your AO.
I had the SBIG AO unit on a previous telescope. AO units really do tame the mount, light winds, cable dragging, etc.
timh
Posts: 377
Joined: Mon Aug 26, 2019 5:50 pm

Re: Centaurus A before and after AO

#7

Post by timh »

Thanks for the explanation Chris,

Fascinating bit of kit of which I wasn't even aware. The problem with applying it to my current set up looks as though it would be back focus - only 55mm from my coma corrector. Definitely food for thought but that will take a little longer to digest ....

Tim
ChrisR Oz
Posts: 119
Joined: Tue Sep 28, 2021 11:03 am
Location: Melbourne

Re: Centaurus A before and after AO

#8

Post by ChrisR Oz »

Wow. 55 mm is not much to play with. That will be a real challenge for optical train.
Good luck thinking about it. It’s those puzzles that make this hobby so much fun.
Cheers, Chris.
Celestron EdgeHD 8, reducer 0.7x, Star Sense, AVX mount and Focuser, CPWI, Starlight Xpress AO, OAG and Filter Wheel, ZWO ASI 294MC Pro and 120MM mini, SharpCap Pro, PHD2, Powermate 2x, Baader Moon & Skyglow, Astronomik CLS-CCD, ZWO Duoband filters.
Post Reply