Re: Milstar 5 video obs

From: Greg Roberts (grr@iafrica.com)
Date: Sat Mar 01 2003 - 12:20:58 EST

  • Next message: Rainer Kracht: "Re: Milstar 5 video obs"

    Hi Brooke
    
    Thank you for your message about video observations. Im sure 
    Rainer will be able to give his own comments so I wont go into 
    too much detail.
    
    ----- Original Message ----- 
    From: "Brooke Clarke" <brooke@pacific.net>
    Sent: Saturday, March 01, 2003 5:34 PM
    Subject: Milstar 5 video obs
    
    
    > But the thing that bothered me about using the integration mode 
    >on a fast moving sat was that if the sat changed pixels then the
    > integration would make the image dimmer.  Or does it just 
    >reduce the contrast?
    
    in the case of Rainer's observations of Milstar 5 - which is 
    essentially in geostationary orbit, the image motion can be neglected 
    in integration times of the order of what Rainer used. In my case I 
    do not have an integration mode and have to use an exposure of 
    1/50th second. On fast moving satellites, such as the shuttle for 
    example, there is a very small amount of trailing which I ignore.
     
    > Have you tried different integration times?
    
    I can only integrate using software and have not tried it on artificial 
    satellites. However Rainer's efforts will no doubt inspire me to try 
    Milstar 5 in this mode.
    
     
    > A 75 mm f1.3 lens is 75/1.3 = 57.7 mm objective diameter and 
    >according to the table on my web page should see MAG 9.5 with 
    >no integration.
    
    this is what I would expect.
     
    > It's interesting that the 82mm/f1.6 = 51.3 mm OD is not as good a 
    >lens.
    
    This was originally an 82 mm f/2 lens which I modified by adding 
    a homemade focal reducer to change it to about f/1.6.
    
    I agree that its not as good a lens as the f/1.3 lens, however my 
    experiences with trying about a dozen different lenses is that aperture 
    is not the prime determining factor but rather the f/ratio. I think this 
    could be because we are dealing with point sources rather than 
    extended objects.
    
    Another factor which affects magnitude limit is the spectral response
    of the ccd chip. The ones we are using are most sensitive in the near
    red portion of the spectrum so red stars appear bright whilst blue or 
    white stars are fainter than expected.
     
    > How do you point the camera?
    
    I would imagine Rainer  either computes the azimuth/elevation of the 
    satellite and uses a mounting equipped with circles to locate the 
    satellite, or alternatively use the stellar background to locate a 
    geostationary satellite.
    
    In my case I use a computer controlled altazimuth mounting carrying
    the ccd camera's - hence the name CoSaTrak ( Computerised Satellite
    Tracking)  and uses freeware software developed by my colleague
    Willie Koorts.
     
    > What is a 1004a?
    
    This is a small printed circuit board carrying a 1/3inch ccd chip 
    which uses the identical technology to the MINTRON Rainer uses.
    The sensitivity is 0.003 lux - unfortunately very little documentation 
    is supplied with the chip and I dont have it to hand at the moment.
    (ie its buried somewhere in my pile of papers!)
    
    However the web-page is http://www.rfconcepts.co.uk/ 
    ( its off-line as I write this so I am unable to get further information 
    at the moment ). The unit is very cheap- costing about 43 U.K. pounds.
    It comes with a small lens which is useless for astronomical 
    applications and one has to mount it in a box and add a power supply
    (+9 to +12v DC). For ordinary use there does not seem to be any 
    advantage in air cooling it with a fan - my latest one is cooled and I 
    cant say I see any difference between the cooled and the uncooled 
    1004x cameras. Incidentally the "a" in the camera model name 
    signifies it is fitted with a small audio board which is of no interest to
    us.  The 1004x is almost on the verge of being dropped and replace
    by the 2005 unit ( if memory is correct). The ccd chip is identical (?)
    to the 1004's and one can purchase a unit in a nice metal box etc 
    for about 3x the price of the lone circuit board if one lacks any 
    mechanical ability.
    
    Like all commercial CCD chips these chips have hot pixels as well as 
    dead pixels - how many you "get" is decided by how lucky you are.
    However I do not find mine objectionable for my satellite work. 
    I believe that the ccd chip also slowly acquires more as it gets more 
    exposure to such things as cosmic ray events etc.
    
    If I can help in any further way please let me know.
    Regards
    Greg
     
    
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