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 Post subject: Saturn - focussing issues
PostPosted: Fri Apr 22, 2011 11:32 am 
I had a proper attempt with the webcam kit last night after a couple of practice sessions and had a go at using the scope as the lens instead of the lenses in the kit.

I decided to try Saturn and ended up with the following using Registax on default settings :

Image

I couldn't really get the focus I wanted. Using the polar alignment and mount motors was great because the object stayed in view all the time but, every time I altered the focus, the scope shook and I had to wait and then try again. I'd heard about people not having enough travel in the focusser but I was able to move either side of the "focussed" image with room to spare.

I've got the same scope as Ian but I've never checked the collimation and I'm using the basic Barlow that came with the scope so it's probably not the best quality. It also seemed a bit hazy with few stars visible.

I could also do with some long USB cables so I can sit inside in comfort and tweak the webcam settings instead of kneeling on the grass in the dark. The 10m ones Dean linked to on Ebay seem not be available anymore.


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 Post subject: Re: Saturn - focussing issues
PostPosted: Fri Apr 22, 2011 6:00 pm 
Hiya Antony, looks like your almost there ...... Did you have the camera on normal or long exposure mode ? did you try whithout the barlow? I have had the same problem with a 2x barlow that to be honest,.........was rubbish.! So could well be the barlow if you can achieve either side of focus with your scope. There was quite a bit of wispy cloud around last night though which affected my images somewhat, making them appear blurry, so that may not be helping.
I have a spare 10m usb you can have as I ordered 2 and only need one so will bring to next meeting for you.
Just a thought though.........did any of your lenses have a slight dew on them when you took the images ??
It's just a bit of fine tweaking thats needed I think, so eliminate the obvious first.
Still not a bad image of saturn with cam so you should be chuffed for a first attempt.


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 Post subject: Re: Saturn - focussing issues
PostPosted: Fri Apr 22, 2011 9:58 pm 
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That's a good first attempt Antony - well done.

When imaging objects which are low in the sky at high magnification, focussing will always be a problem, since atmospheric turbulence will cause the target to appear to "wobble" in and out of focus even if you've got it spot on!

Bear in mind that the "seeing" will vary from night to night (hazy but very still nights are often the best). You should also try to avoid imaging over warm objects (radiating thermal currents) like house roofs: trees are better. And allow your 'scope to cool down outside for an hour before starting, to minimise circulating air currents inside its tube.

Now (unless you've got a remote electric focus?) there's no need to worry about extending your camera leads, since you'll need to be beside your 'scope to be able to reach the focus knob!

My technique is to tweak the focus in and out a few times (allowing time for the image to settle after each adjustment before assessing the result) to try to find the best "average" setting. And I try to re-optimise the focus in this way before each imaging run, hoping that I'll get at least one good result in an evening (although I won't know how successful I've been until I've processed all the AVI files the following morning!).

More details at our talk on 3-May...


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 Post subject: Re: Saturn - focussing issues
PostPosted: Sat Apr 23, 2011 10:49 am 
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AWalmsley wrote:
Using the polar alignment and mount motors

You've already got over the first hurdle. By having good tracking it gives you time to play. Well done!

AWalmsley wrote:
I'm using the basic Barlow that came with the scope

I'm using the basic x2 barlow that came with my original scope. Seems to do okay.

RWilkinson wrote:
unless you've got a remote electric focus?

I started to getting results when my electric focus arrived. Depending on your telescope I ordered mine directly from JMI Motofocus after no-one was willing to order for me. It took a month to arrive. :roll: Untill then it was up the ladder, down the ladder......

With that aside your image is looking good!!! I wouldn't worry about the barlow lens

_________________
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I choose to image with an 11" SCT Celestron in this decade and do the other things, not because they are easy, but because they are hard......


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 Post subject: Re: Saturn - focussing issues
PostPosted: Sat Apr 23, 2011 8:40 pm 
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Antony,
Well done for first attempt!!!!!
When imaging a planet low in the sky with a colour camera you will always struggle to get focus as the 3 colours (RGB) are displaced vertically - atmospheric dispersion is the problem. This blurs the image even when in focus. When processing you can (and should) displace the 3 colour planes back into alignment. I don't do much planetary imaging these days but I always imaged when the Moon was around and focused on that!


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 Post subject: Re: Saturn - focussing issues
PostPosted: Sat Apr 23, 2011 9:11 pm 
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DRatledge wrote:
When imaging a planet low in the sky with a colour camera you will always struggle to get focus as the 3 colours (RGB) are displaced vertically - atmospheric dispersion is the problem. This blurs the image even when in focus. When processing you can (and should) displace the 3 colour planes back into alignment.

There's an example of this in my earlier post:
http://www.boltonastro.org.uk/Forums/viewtopic.php?f=4&t=130
and we'll attempt a live demonstration on 3-May.


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 Post subject: Re: Saturn - focussing issues
PostPosted: Mon Apr 25, 2011 9:00 pm 
Having enlarged the image to 400%, I can indeed see that there is a red tint at the bottom and a green-blue tint at the top. I'll try again after the next meeting then I can see what detail I have captured.


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 Post subject: Re: Saturn - focussing issues
PostPosted: Wed Apr 27, 2011 7:28 pm 
Couldn't resist watching a few tutorials on YouTube and found out how to shift the colours. I think I overdid some of the adjustments. Need to work on improving the quality (and size) of the source image to get a better end result.


Attachments:
Saturn3.png
Saturn3.png [ 6.8 KiB | Viewed 7104 times ]
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 Post subject: Re: Saturn - post-processing
PostPosted: Thu Apr 28, 2011 6:30 am 
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Try the Histrogram stretch, RGB Balance and Rotate functions next:
Attachment:
File comment: I did some more post-processing on Antony's image in RegiStax
Saturn3.jpg
Saturn3.jpg [ 2.48 KiB | Viewed 7097 times ]


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