Imaging Saturn

[timh]

Images taken between 9 and 10 pm on 31/10/ 26 with seeing gradually deteriorating.

Orion Optics (UK) VX12 300 mm F4 Newtonian - modified by OO to eliminate flexure, adjustable focuser alignment and resurfaced mirror - Baader clicklock, 2X ED Barlow and Pegasus focuser controller on a CEM70G mount.

ASI 715 MC 1.45 u pixel camera at ~ correct distance from Barlow for 2 X (i.e. ~ 0.137 arcsec/ pixel at F8). Filter was ZWO IR/UV cut filter for visible light image and Astronomik Proplanet 642 filter for far red and near IR images

The visible image comprised seven video .ser captures with Sharpcap at 9.07, 9.09, 9.16, 9.18, 9.19, 9.21 and 9.24 pm comprising a range of capture times from 60s to 120 s and 5400 to ~11000 frames of 11ms at a gain of ~330. Depending on the quality BiggSky selected between 30 and 50% of each capture for stacking. The 7 stacks were deconvolved in BiggSky -- the ROI - based psf first being obtained from the luminance of the aligned channels - and then this used to rerun the colour deconvolution. The seven images were then de-rotated to 9.16 pm and combined together in WinJupos. The combined image was then further slightly wavelet sharpened in PixInsight and finally brightened in Affinity photo. The process for the mono red/IR image was similar except that only 5 images were combined.

The two images both show a 'ring' artifact at the inside perimeter and without the edge of the planet disk. This is likely because all of the captures were somewhat underexposed (because I was overly cautious about including overexposed frames). I note that (as is so often the case) there is a Sharpcap option to match the need that masks overexposed pixels and that could certainly be worth a try next time along with taking the histogram up nearer to 100%. Secondly - based on a few pilot experiments - it was probably a mistake trying to get more frames at the expense of quality. The exposure time of 11 ms was likely too short and 15 or 16 ms probably nearer the sweet spot for Saturn? The IR image likely suffered because conditions had deteriorated further.

[turfpit]

Tim

BiggSky selected between 30 and 50% of each capture for stacking

In my experience of the software this indicates poor conditions. In good conditions, I regularly see 70 - 90% of frames stacked.

The image below shows the output from SER Player, the important capture details and the final processed result (stack 27% + decon). The camera used was an Altair 183C (2.4µm). A gain of 4000 (out of 5000) was used. I tend to use gain of ~80% for Saturn (~70% for Jupiter) and aim for 70-80% histogram saturation allowing for the difference in the RGB graphs. That gives me decent results (sometimes). Conditions are the enemy above the turbulent Pennines.

Saturn_Capture.JPG (58.51 KiB) Viewed 75 times

You might find https://biggsky.com/derotation-manual.html useful. The documentation has undergone a massive update. This https://biggsky.com/manual.html?doc=lunar-planetary was contributed by me plus some of my data was used in the Lunar Mosaics section.

Dave

[timh]

Thanks once again Dave. Very useful information and links! I have just downloaded the up to date version of Biggsky and I had no idea that the software now includes derotation and so interesting to see how that compares with Winjupos.

The histogram saturation curves you show are useful .. I cautiously kept green at below about 75% ... the comment on underexposure likely causing disk edge artifacts was from a friend at Reading Astro Soc. who is an experienced planetary imager -- and it seems to make sense and to be consistent with your saturation levels being higher. Incidentally did you use the Sharpcap option to mask overexposed pixels?

At 33 ms your exposures are way longer than mine - (3X) and - correspondingly - I think that my gain was taken too high at nearer 90%. With about 2X the light gathering of an 8 inch probably something like 17 ms and a gain of 75% should be where to head next (if the weather permits) ?

As you suggest the seeing clearly wasn't great and I was pleased to get images as good as above. Captured a lot that was far worse over 3 nights.

Anyway I'll get stuck into reading those two Biggsky links

Tim

[turfpit]

Tim

did you use the SharpCap option to mask overexposed pixels?

No. I stick to basics and trust that a decent histogram will be enough.

A lot of the knowledge comes from trial and error both in the capture and the processing.

Enjoy the (heavy) reading.

Dave