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 Post subject: Imaging Saturn in May 2013
PostPosted: Fri May 03, 2013 7:01 am 
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Location: Bolton
This planet won't be well-placed for Northern hemisphere observers over the next few years: it will be low in the sky over our Summer months, so it's more of a challenge to image.

I put my 8" SCT out in the garden to start cooling just before 9pm, and set up my tripod twenty minutes later. I made a good guess when positioning it, since I could see Polaris in the polar-scope. I'd set up my laptop just inside the kitchen window, connected via a long serial lead to the mount and a 5m USB extension to the webcam. I also had a long extension to my focus-motor.
With the tiny webcam sensor behind an effective focal length of more than 7m, the 'scope needs to be pointed accurately, but I had Saturn on my screen just after 9:30. At this point the seeing was appalling - wobbling all over the place, but I captured a video stream just in case it should cloud over later. At this point I could see a couple of dust-specks on the sensor, so I brought the camera indoors and cleaned it.

I returned every half-hour to see if things had settled down, but as my tracking was a bit off I had to re-point the 'scope each time - a very quick job, thanks to my flip-mirror. By 11pm the image was much clearer, but the planet was about to "set" behind next-door's roof, so this was the last (and clearest) video I captured.

I use the NexStar Control Pad program to adjust the pointing of my mount from indoors. It's a simple utility with which it's very easy to alter the rate and direction of the control buttons. I needed to make corrections every few minutes to keep the planet centred on the sensor.
Instead of wxAstroCapture I tried the SharpCap program - this was just as easy to use, and I found that its ability to RGB align the incoming video "on the fly" made the image look much clearer on the screen - and so easier to focus. When a planet is low in the sky it's light is badly refracted by the thick layer of Earth's atmosphere, and so the colours are smeared out across the sensor - the RGB align function allows us to re-combine the three colours so that the image is much sharper. (Note that it just does this on the displayed image - the captured video is not processed, so we still need to run the RGB align in RegiStax when doing the post-processing).
Operating at round f/37, the image was pretty dim (especially with some hazy cloud around), so I had the camera set at 5 fps and the video gain wound up to around 70% in order to get a reasonable signal. My captures are 450 frames, which produces .AVI files of around 200MB each.

Then this morning I processed my last three video streams using RegiStax 5.1 (version 6 won't run on that laptop). The latest one was the best: I stacked the clearest 360 of the 450 frames to produce the result which I've loaded into my Gallery: http://www.boltonastro.co.uk/gallery/displayimage.php?pid=1226&fullsize=1


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 Post subject: Re: Imaging Saturn in May 2013
PostPosted: Fri May 03, 2013 8:35 am 
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Joined: Sat Feb 25, 2012 10:57 am
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Great masterclass Ross, thanks.

I was out last night too practising polar alignment with Alignmaster and scope control with Stellarium with some success but as you say the seeing was not very good. You managed a good image of Saturn though despite this.

Regards


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 Post subject: Re: Imaging Saturn in May 2013
PostPosted: Tue May 07, 2013 2:02 pm 
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Location: Bolton
I had another go at Saturn last night, but the air was a lot less stable than last Thursday.
With the planet coming to oppostion in the summer months it's low down in the SE, so I'm seeing it above the roofs of nearby houses (which tend to re-radiate heat in the evening after a warm sunny day), so that's not a good direction for me. It was much better a few years back, when it was at opposition in the winter and so high in the East (and viewed over the trees in the park from here).

So as it's unlikely that I'll get any better conditions than last Thursday, I did some more work on my penultimate video-stream from last week - this time doing the stacking and RGB aligning in RegiStax 5.1, and then exporting this result (as a 16-bit TIFF) into IRIS to do the rest of the processing there.
I think that I've teased out a little more detail now - the cloud-belts and Cassini division are certainly clearer:
Attachment:
File comment: Saturn on 2-May-2013. Best 160 of 450 frames, processed in RegiStax & IRIS.
Saturn 02_05_2013 23_02_v2.jpg
Saturn 02_05_2013 23_02_v2.jpg [ 10.29 KiB | Viewed 3003 times ]


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