Optical 30 Nov 2012

From: Greg Roberts (grr@telkomsa.net)
Date: Sat Dec 01 2012 - 14:57:41 UTC

  • Next message: Marco Langbroek: "Re: Optical 30 Nov 2012"

    Observations 19 NOV 2012 Part 4 last
    ------------------------------------
    
    Cosatrak 1 (Computerised satellite Tracking System).
    Images processed and measured manually.
    
    Site 0433 : Longitude 18.51294 deg East, Latitude -33.94058 deg,
    Elevation 10 metres-situated in Pinelands (Cape Town),South Africa
    
    FOR CLASSFD.TLE:
    ----------------------
    23223 94 054A   0433 F 20121130194231050 17 15 0356076+055803 19
    23223 94 054A   0433 F 20121130194401550 17 15 0357402+060122 19
    23223 94 054A   0433 F 20121130194536250 17 15 0359116+060537 19
    24680 96 072A   0433 F 20121130203744900 17 15 2209243-492359 19
    24680 96 072A   0433 F 20121130203759900 17 15 2224121-433111 19
    33490 09 001A   0433 F 20121130190927500 17 15 0258595+065731 19
    33490 09 001A   0433 F 20121130191223200 17 15 0301561+070007 19
    33490 09 001A   0433 F 20121130185643550 17 15 0246129+064608 19
    36105 09 066B   0433 F 20121130200827300 17 15 0846157-512656 19
    36105 09 066B   0433 F 20121130200847300 17 15 0818129-491538 19
    37233 10 063B   0433 F 20121130190927500 17 15 0252342+085910 19
    37233 10 063B   0433 F 20121130191223200 17 15 0255474+085455 19
    37233 10 063B   0433 F 20121130185643550 17 15 0238375+091658 19
    38528 12 034A   0433 F 20121130194246050 17 15 0358049+083435 19
    38528 12 034A   0433 F 20121130194416550 17 15 0359348+083417 19
    38528 12 034A   0433 F 20121130194546250 17 15 0401035+083326 19
    
    
    STRAYS SEEN:
    -----------------
    25626 99 005A   0433 F 20121130194401550 17 15 0400283+052129 19
    25922 99 052A   0433 F 20121130185643550 17 15 0251161+052238 19
    25922 99 052A   0433 F 20121130191223200 17 15 0306588+052253 19
    26590 00 068A   0433 F 20121130185643550 17 15 0250444+052243 19
    26590 00 068A   0433 F 20121130191223200 17 15 0306278+052303 19
    26666 01 002A   0433 F 20121130185643550 17 15 0237212+052506 19
    27825 03 026A   0433 F 20121130185643550 17 15 0246165+064536 19
    28089 03 053A   0433 F 20121130194401550 17 15 0356558+060043 19
    28885 05 041B   0433 F 20121130185643550 17 15 0259364+052038 19
    33056 08 030B   0433 F 20121130185643550 17 15 0237166+052234 19
    36095 09 063A   0433 F 20121130190907200 17 15 0315235+061605 19
    38014 11 077A   0433 F 20121130185643550 17 15 0239207+052140 19
    38245 12 016A   0433 F 20121130185643550 17 15 0302230+052013 19
    
    NOTES:
    ----------
    (1) In a weak moment, and feeling like an early Christmas since
        the nuts are predicting the earth is coming to an end before
        Christmas, I purchased a NIKON D3100 DSLR camera that was on
        a "special". Naturally I was interested to see how it would
        perform satellite wise.
    
    (2) Whilst not as good as my ccd camera-which costs a great deal
        MORE - some useful work could be done with this and similar
        DSLR cameras. Much experimenting would be required as one can
        manually set such items as aperture, f/ratio, ISO value (this
        is the "sensitivity"), size of image in pixels - the more
        pixels the better the image scale and hence resolution and
        other items not so important like white balance, noise
        reduction etc
    
    (3) The main problem is timing accuracy. This particular camera
        gives the time the image was taken to the nearest 0.1 second
        using its internal clock which the user must set. At start of
        the observing session I set the camera clock to the nearest
        second against my GPS digital display to 0.xx seconds.
        I then photographed the display and this gave the "time offset
        error".
        At the end of the observing session I again photographed the
        GPS display and got the new time offset error. This showed
        that the camera clock drifted +0.3 seconds in 195 minutes.
        I made the assumption that the clock error is linear but for
        high altitude satellites were a timing accuracy of 1 second
        is usually adequate this is not a problem but I applied this
        correction to all the times determined.
    
    (4) I also tried two LEO sats and applied the time correction.
    
        The assumption was made that a 30 second exposure was
        exactly 30.0 seconds - something which should be checked!
    
    (5) I DO NOT intend using this camera for regular observing
        but it might come in use sometimes as it has a much wider
        field of view than my normal set-ups.
    
    (6) As am example of size of field of view - I used the
        telephoto lens set at the following focal lengths
    
                200mm         field of view  6.6 x  4.4 degrees
                135mm         field of view 10.1 x  6.7 degrees
                 80mm         field of view 16.0 x 10.5 degrees
    
        In all cases with an exposure of 20 to 30 seconds at f/3.5
        I was able to record star trails down to about magnitude
        +11.5,  Naked eye I could not see stars fainter than about
        mag +3.5 at best.
    
    (7) I did not find any useful difference in magnitude gain
        whether "shooting" at f/2.8 or f/3.5 and found that I got
        best results using f/3.5 or f/4.5 - this will of course
        depend on the users sky - mine is VERY bright . I have
        still to experiment with various ISO values - I used ISO
        800 and 400 - the camera can go a lot more (6400 up to
        12800) but I think these would be useless in a bright sky
        as the image will just be completely "whited" out.
    
    (8) Overall I am happy with the results the camera gave, so if
        you have a half decent DSLR then give it a go.
    
    (9) Since one is imaging moving objects ( satellites) one
        cannot use any of the "stacking" programs to improve the
        background noise level - which at ISO 400 and 800 is not
        bad at all. Hot or dead pixels were not obvious but there
       were occassional bright pixels due to cosmic ray strikes
       etc so always best to take two images of a geostationary
       field to verify that the bright pixel is a real satellite.
    
    Cheers
    Greg
    
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