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Posts posted by Shibby

  1. Hi. I'm partly commenting to agree with others about your flats, these dust rings are almost certainly from the camera's sensor window judging by their size and they should calibrate out no problem. You can always take a blower to the window to try and reduce them. The first flat does seem to have a separate issue, though. Is it the refresh of your LED panel?

    Secondly, I just wanted to say that your observatory is a real beauty!

    • Like 2

  2. As you suggest, it's probably down to field distortion due to your optics. I can't think of any easy way around that, other than cropping or avoiding the flip when using a particular filter.

    I'm not sure about your concern with registar - you may get away with it, because even in order to rotate an image the stacking software will surely be messing with the pixels of each sub and that seems to work okay? Why don't you give it a trial and see what happens?

    • Like 1

  3. I recently finished capturing data for a bi-colour image of the wall in NGC7000. It's taken about a month, which I suppose isn't that bad all things considered!

    As I'm sure you're aware, this is one of the brighter regions in the 1700 lightyear-distant North American Nebula. Although huge (estimated 100 lightyears across), NGC7000 is believed to be mostly 'lit up' by a single giant star HD 199579, also known as Miro's Diamond. You could call the nebula V37 if you wish, as Herschel designated it #37 in his 'V' catalogue when he discovered it - the 'V' standing for Very large :)

    The image is a bi-colour, 2-panel mosaic with total integration time of around 13.5 hours. Processing is just curves in Photoshop with a star layer to prevent star bloat, especially in Oiii, with which the Baader filter gives a few halos on the brighter stars. I don't know if I've combined the layers in a sensible manner, I just pasted the Oiii in to the green and blue layers then tweaked it down a bit in the green. I was aiming for roughly 'natural-ish' looking colours, although it looks massively different on my two monitors. Any feedback on that is appreciated.

    Thanks for looking!

    Hα: 2x24x600s
    Oiii: 2x17x600s

    Optics: MN190
    Camera: 460ex
    Mount: AP Mach1GTO
    Guding: Orion mini 50mm guidescope & QYH5L-ii

    [direct link]


    You may not like the colour combination, but if you're interested here are the separate channels so you can see the difference between hydrogen and oxygen





    • Like 11

  4. Well, I'd been waiting 12 days for a clear night (also to gather further data on NGC7000) so was determined to get some data whatever the conditions! My guiding was averaging ~0.7" RMS, so I hope the data will be good enough. I think the altitude of the nebula helped somewhat. I've just checked FWHMs and they're only 0.5 higher than the previous session.

    1 hour ago, kirkster501 said:

    A good opportunity wasted

    It is frustrating when you miss an opportunity, knowing how infrequent they can be in our country. But you have to remind yourself there will eventually be others!

    5 hours ago, ollypenrice said:

    Because my sleep's all over the place I'm up early and have just seen Orion high and mighty in a clearing sky.

    Work is already a struggle this morning! The comforting prominence of Orion isn't a bad reward for powering through :)

    • Like 1

  5. I agree with pretty much everything that's been said. Use your DSLR on a tracking platform such as the Star Adventurer or - if you don't need high portability - find a second-hand, motorised, equatorial mount.

    I'm not certain how you came to the conclusion of a small refractor on a tripod, because this really won't help you at all with astrophotography over what you currently have! If you want to try lunar/planetary then look into a high frame-rate camera for your dob. If you want to try long exposure using your DSLR, the key is the tracking platform, with which you can initially use your existing lenses to get started.

    Anyway, as you've quite rightly decided, definitely digest a few books and do some further reading first. Then, take the first tentative steps onto the slippery slope ;)

  6. Just checking, when you say vignetting, do you mean circular? That would be odd, suggesting that it's caused by something between the prism and guide camera.

    If the vignetting is from the edge of the main imaging circle then, as others have said, you need to move the prism as close as you can to the main camera's sensor without overlapping. Moving the prism in/out has no effect on focus - remove the whole reducer/OAG/camera assembly and look back towards the main sensor while moving it into position.

  7. I'm a bit surprised that the Altair guide scope only suggests guiding 500mm focal length.

    FWIW, my guide-scope is a mere 162mm in focal length and I have no trouble guiding my 1000mm FL scope at 1.14 asec/pix.

    The guide camera does have pretty small pixels at 3.75µm. This gives a 4.77 asec/pix and a healthy enough ratio of 1:4.2 (You'll often here 1:5 quoted as a maximum).

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