Optical 16 May 2012

From: Greg Roberts (grr@telkomsa.net)
Date: Thu May 17 2012 - 12:36:20 UTC

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    Observations 16 MAY 2012
    ---------------------------------------
    
    Cosatrak 1 (Computerised satellite Tracking System).
    
    FLI ML8300M CCD camera with mechanical shutter + Trimble GPS 
    
    Used with NIKON ED AF NIKKOR 80-200mm f/2.8 telephoto lens
    set at ~150mm focal length. Field of view 6.9 x 5.3 degrees,
    Time is accurate to within 50 milliseconds. 
    
    Site 0433 : Longitude 18.51294 deg East, Latitude -33.94058 deg,
    Elevation 10 metres-situated in Pinelands (Cape Town),South Africa
    
    FOR CLASSIFIED.TLE:
    --------------------------------
    33490 09 001A   0433 F 20120516170050448 55 15 1150153+063050 58               
    33490 09 001A   0433 F 20120516170938596 55 15 1159031+062301 58               
    33490 09 001A   0433 F 20120516171942275 55 15 1209074+061354 58               
    33490 09 001A   0433 F 20120516175332706 55 15 1242550+054253 58               
    20963 90 097B   0433 F 20120516172219235 55 15 1428115+033029 58               
    20963 90 097B   0433 F 20120516172753801 55 15 1433222+030748 58               
    20963 90 097B   0433 F 20120516173616716 55 15 1442008+022951 58               
    20963 90 097B   0433 F 20120516174059622 55 15 1446414+020949 58               
    25967 99 063A   0433 F 20120516172219235 55 15 1416194+063107 58               
    25967 99 063A   0433 F 20120516172753801 55 15 1421335+062441 58               
    25967 99 063A   0433 F 20120516173259825 55 15 1427005+061829 58               
    15543 85 010B   0433 F 20120516174312949 55 15 1509336-041846 58               
    15543 85 010B   0433 F 20120516174627868 55 15 1512459-043154 58               
    15543 85 010B   0433 F 20120516174844714 55 15 1515008-044136 58               
    27168 02 001A   0433 F 20120516163538177 55 15 1020413+104108 58               
    27168 02 001A   0433 F 20120516164042579 55 15 1025467+103907 58               
    27168 02 001A   0433 F 20120516164929423 55 15 1034364+103500 58               
    19976 89 035A   0433 F 20120516163538177 55 15 1021283+103439 58               
    19976 89 035A   0433 F 20120516164042579 55 15 1026297+102718 58               
    19976 89 035A   0433 F 20120516164929423 55 15 1035119+101414 58               
    33491 09 001B   0433 F 20120516165145125 55 15 1129121+063227 58               
    33491 09 001B   0433 F 20120516165345186 55 15 1130590+063049 58               
    33491 09 001B   0433 F 20120516165736992 55 15 1134307+062805 58               
    33491 09 001B   0433 F 20120516170050448 55 15 1137250+062517 58               
    35815 09 047A   0433 F 20120516165145125 55 15 1119354+053251 58               
    35815 09 047A   0433 F 20120516165345186 55 15 1121370+053308 58               
    35815 09 047A   0433 F 20120516165736992 55 15 1125287+053315 58               
    35815 09 047A   0433 F 20120516170050448 55 15 1128406+053244 58               
    35815 09 047A   0433 F 20120516170938596 55 15 1137312+053246 58               
    35815 09 047A   0433 F 20120516171942275 55 15 1147341+053218 58               
    
    STRAYS SEEN:
    ------------------
    12618 81 069A   0433 F 20120516165345186 55 15 1137206+044320 58               
    27825 03 026A   0433 F 20120516170050448 55 15 1149463+063525 58               
    22931 93 078B   0433 F 20120516171942275 55 15 1155166+082938 58               
    25010 97 062A   0433 F 20120516172219235 55 15 1432462+051242 58               
    38107 12 013A   0433 F 20120516172219235 55 15 1433139+050846 58               
    32779 08 019A   0433 F 20120516172219235 55 15 1435202+050402 58               
    37344 11 001A   0433 F 20120516172219235 55 15 1430571+050955 58               
    33108 08 033A   0433 F 20120516172219235 55 15 1440298+052858 58               
    29163 06 020B   0433 F 20120516172219235 55 15 1441319+050352 58               
    32295 07 056C   0433 F 20120516172219235 55 15 1425165+051128 58               
    25924 99 053A   0433 F 20120516172219235 55 15 1426310+050755 58               
    21111 91 010A   0433 F 20120516172219235 55 15 1426473+051450 58               
    23968 96 042B   0433 F 20120516174059622 55 15 1452195+054056 58               
    27298 02 002A   0433 F 20120516172219235 55 15 1422240+050645 58               
    32050 07 037A   0433 F 20120516172219235 55 15 1422329+051038 58               
    37934 11 069B   0433 F 20120516172219235 55 15 1419370+053851 58               
    27525 02 043A   0433 F 20120516191341354 55 15 1614000+055024 58               
    23766 96 002C   0433 F 20120516191341354 55 15 1624384+054924 58               
    16199 85 102A   0433 F 20120516174312949 55 15 1510125-033153 58               
    14783 84 022A   0433 F 20120516174312949 55 15 1506175-055647 58               
    26487 00 052A   0433 F 20120516165345186 55 15 1132400+060917 58               
    
    NOTES:
    -----------
    (1) Did not intend to observe but long range weather prediction
        indicated bad weather for the next few days so thought I had
        better check up on the two unknowns observed on the 14 May
        and I wanted to try a few experiments.
    
    (2) Unknown 1 is in fact APSTAR 7- the elset I had was two days
        old and indicated that the satellite was still drifting. As
        Mike pointed out the later elset indicated the satellite was
        now stationary and thus the unknown so that ones solved.
    
    (3) Unknown 2 is almost certainly the missing PAN. It is still
        drifting very slowly to the west and it looks like 
        HELLAS SAT 2 could be the next target.
    
    (4) Did some more experiments. By measuring star trails at corners
        and in centre I find the following
    
                        Top left corner     49.9 mm
                        Top right corner    47.1 mm
                        Centre              47.9 mm
                        Bottom left corner  47.1 mm
                        Bottom right corner 49.7 mm
    
         In addition I have a field rotation of about 4 to 5 degrees in
         going from left to right edges. Offhand I dont have a physical 
         explanation so is this due to defects in the camera lens ?
    
         Since I am constantly changing the lenses that are used with 
         the camera I dont know if its really worth while trying to
         improve these figures since the system is not static.
    
    (5)  I did try reducing the aperture. To date I have been using the
         lens at f/2.8. I tried f/4.0 with a significant improvement in 
         image quality, especially in the corners so I went to f/5.6 and
         even better quality. This is effectively reducing the aperture
         of the camera from 150/2.8 = 54 mm, to 150/4 = 37.5 mm, to 
         150/5.6 = 26.8 mm so loosing magnitudes. One can compensate for 
         this by using longer exposures as one stops down from f/2.8 to 
         f/5.6, for example  30 sec at f/2.8 is roughly equal to 60 sec 
         at f/4  or 120 sec at f/5.6. As the geostationary satellites are 
         barely moving and are effectively a point source they integrate 
         well and appear to have the same brightness throughout but star 
         trails get longer and fainter as exposure increases. 
         At f/2.8 the faintest star trail is about mag +12 but at f/5.6 
         the faintest trails are about mag +9 so one has to decide what 
         is optimum and for the present f/4 seems a good bet.
         A disadvantage of using too long an exposure is that the star
         trails become too long which means less star trail ends to use 
         as a reference measure. In addition the image is criss-crossed 
         with leo satellites that passed through the field of view in 
         the (say) 300 seconds exposure.
    
    (6)  The current field of view is about 6.9 x 5.3 degrees with a focal
         length of about 150 mm and if 1 bin mode is used for the CCD camera
         the image scale is 7.6 arc seconds per pixel. Next time I fiddle
         with the camera I will decrease the focal length to give about a 
         10 deg field - this makes the system even better for searching
         for satellites or observing satellites a long way off time.
    
    (7)  I will continue measuring the geo survey images secured 14 May-
         will keep me busy while it rains outside :-))
    
    (8)  For leo sat work I propose to use a 10 degree field with camera
         in 4 bin mode for high sensitivity. If the positional resolution
         proves inadequate I could go to using 3 bin or even 2 bin mode
         but the lower the bin numer the bigger the image
              4 bin is about 1 Mbyte whilst 1 bin is about 13 Mbytes.
    
    (9)  The term "bin" may not be familiar to non- CCD uses. With 1 bin one
         uses the CCD camera at maximum resolution.( 1 bin = 1 pixel).
         2 bin means the light from 2 pixels are summed together , which 
         means half the maximum resolution but double the sensitivity of 
         1 bin. Similarly 4 bin means adding the light from 4 pixels into 
         one, reducing resolution by 4 but increasing sensitivity to 4 
         times that of 1 bin mode. For leo satellites I use 4 bin mode but
         for geosats use 1 mode.
    
    (9)  Sorry for the "details" but this might help other observers who
         are contemplating using CCD cameras for satellite work.
    
         Anyway my wife is always telling me I "talk" too much!
    
    Cheers
    Greg
    
    
     
    
    
    
    
    
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    This archive was generated by hypermail 2b29 : Thu May 17 2012 - 12:39:19 UTC