Re: Using a DSLR

From: Marco Langbroek (marco.langbroek@online.nl)
Date: Fri Dec 14 2012 - 21:47:38 UTC

  • Next message: Brad Young: "BY F to 121512"

    Op 14-12-2012 21:33, Greg Roberts schreef:
    >
    > Have no problems with the discussion about "live focus" using modern DSLR
    > cameras. Ive just purchased a NIKON D3100 which has this feature - I focus on a
    > bright  star - its easy to see and brightness depends on the f/stop of the lens
    > used since you are actually viewing through the lens - then use the zoom feature
    > in "live view" - its actually just a magnified image of the initial image and
    > not a true zoom but there is no problem seeing where the image is sharpest.
    
    To be clear: that is true only for the Nikon D3100. With the canon EOS, you 
    truely zoom in on the sensor pixels.
    
    About the lens choice: for LEO I use a 2.5/50mm stopped down one stop to 2.8; 
    for fast LEO (Keyholes near perigee, objects near decay) I use a 2.0/35mm at 
    F2.0 because of the larger FOV, and for faint LEO I use an 1.4/85mm at F1.4 
    (this lens, a SamYang 1.4/85mm which is made with fittings for several camera 
    brands, I can truely recommend, it is marvelous!).
    
    For HEO I use a Zeiss 2.8/180mm. I used this for some time for GEO as well but 
    now use the 1.4/85mm for that as it has a larger FOV but almost the same light 
    gathering power (aperture). I still us the Zeiss for HEO because it better shows 
    the tiny satellite trails.
    
    I work at ISO 800-1000 for LEO and GEO, sometimes 1600 for HEO in the zenith. 
    How high an ISO setting is feasible depends on your sky AND the noise 
    characteristics of your camera (my new EOS 60D is much better with respect to 
    noise at high ISO than my 450D was).
    
    I generally use 10 second exposures (as I initially calibrated my camera for 10 
    second exposures, and it is s fitting exposure for a 50mm lens on LEO objects). 
    In strong twilight I sometimes take shorter exposures.
    
    In my experience aperture actually does make a difference: stopping a 2.5 lens 
    down to 3.5 does mean you'll lose in limiting magnitude.
    
    - Marco
    
    -----
    Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
    e-mail: sattrackcam@langbroek.org
    
    Cospar 4353 (Leiden):   52.15412 N, 4.49081 E (WGS84), +0 m ASL
    Cospar 4354 (De Wilck): 52.11685 N, 4.56016 E (WGS84), -2 m ASL
    Station (b)log: http://sattrackcam.blogspot.com
    Twitter: @Marco_Langbroek
    -----
    
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