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  1. #1
    moxican's Avatar
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    Default Sampling in a big city



    I would need some help determining the angular resolution in a big city. I am in Toronto, Canada (absolute white zone). I did some research and it says that depending on the location it should be between 3"-5". What's the angular resolution that experienced imagers use in this area, or anyone whose imaging from a big city? The equipment I mostly use for DSO photography is a Celestron C80ED. It's an F7.5 which is decent. If I put my T3 on it it gives me sampling of 1.78"/pixel. I think that should be ok. Or not Basically I just wanna squeeze the max performance out of my equipment. Any suggestion is welcome.
    Gusztav

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  2. #2
    Phil Leigh's Avatar
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    Default Re: Sampling in a big city

    I'm not sure I follow. Angular resolution is determined by the focal length of the scope and the pixel size of the camera. I don't think that light pollution conditions can alter that.
    Normally you choose a combination of focal length and pixel size based on the size of the thing you are trying to image, so planets require much greater focal length and a sensor with a smaller number of larger pixels... Whereas large DSO's require less focal length and a bigger sensor because the target needs a large field of view to fit it all in.
    Telescope: SWEquinox ED80 Pro (Schott/Ohara Fluorite)+Baader Steeltrack, C8 XLT Mount: Skywatcher HEQ5 Pro, Rowan belt drive on Pillar mount+EQDIR+ADM saddle/dovetails Camera: JTW1100D mono , CentralDS 600, ASI120MM. ASI120MC, IDAS & Baader NB 2-inch filters, TS Filter Drawer System Accessories: TV Nagler T4 12 mm, Baader 8-24 MkIII, Ortho 5mm, Aspheric 31mm, Meade 12mm reticle, TV Powermate 2x & 2.5x, JMI+BAST Motorfocus+FCUSB, TV 0.8x FR/FF, Celestron 0.63FR, Orion RACI & Mag Mini, Canon IS 15x50 Bins
    Software: EQMOD/Stellarium/Autostakkert!/Registax/BackyardEOS/PixInsight,PHD2,AlignMaster, AstroTortilla, Straton

  3. #3
    moxican's Avatar
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    Default Re: Sampling in a big city

    Oh sorry I wasn't clear. I meant to image DSO's. Of course there are situations when I the field of view is at most importance with larger DSOs. But in order to achieve max resolution at the end sampling plays a role. At least that's what I've read here for example: Sampling and Pixel Size « Catching the Light
    Gusztav

    Scopes: C9.25 Starbright XLT; Celestron C80ED; Celestron 70 Travelscope;
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  4. #4
    Phil Leigh's Avatar
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    Default Re: Sampling in a big city

    Quote Originally Posted by moxican View Post
    Oh sorry I wasn't clear. I meant to image DSO's. Of course there are situations when I the field of view is at most importance with larger DSOs. But in order to achieve max resolution at the end sampling plays a role. At least that's what I've read here for example: Sampling and Pixel Size « Catching the Light
    Jerry's page you linked to is talking ONLY about planetary - which is where the effects the effects of atmospheric seeing (but NOT light pollution!) play a major role. Also, for planetary the issue of under/over sampling becomes important - exactly as he states on that page.

    Which is why for PLANETARY work with a DSLR you should shoot in ultra-high quality 5X liveview 1:1 sensorixel mode (as you would if using BackyardEOS or APT for example) - you only use a small part of the sensor (one fifth of its area) but you are going to be sampling the planet properly with a suitable scope (1500-4000mm of focal length normally).

    Note that for the Canon 550D, 60D and 60Da the 640x480 crop mode is also 1:1 (and capable of 60fps!) so you should use that for planetary capture. For all other Canons with LiveView, the LiveView 5X capture method is the only way to get 1:1 (i.e. best quality) results.


    None of this applies to DSO imaging.
    Cheers
    Phil
    Telescope: SWEquinox ED80 Pro (Schott/Ohara Fluorite)+Baader Steeltrack, C8 XLT Mount: Skywatcher HEQ5 Pro, Rowan belt drive on Pillar mount+EQDIR+ADM saddle/dovetails Camera: JTW1100D mono , CentralDS 600, ASI120MM. ASI120MC, IDAS & Baader NB 2-inch filters, TS Filter Drawer System Accessories: TV Nagler T4 12 mm, Baader 8-24 MkIII, Ortho 5mm, Aspheric 31mm, Meade 12mm reticle, TV Powermate 2x & 2.5x, JMI+BAST Motorfocus+FCUSB, TV 0.8x FR/FF, Celestron 0.63FR, Orion RACI & Mag Mini, Canon IS 15x50 Bins
    Software: EQMOD/Stellarium/Autostakkert!/Registax/BackyardEOS/PixInsight,PHD2,AlignMaster, AstroTortilla, Straton

 

 

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