Using a DSLR (was Re: North Korea satellite observed)

From: Marco Langbroek (
Date: Fri Dec 14 2012 - 11:11:08 UTC

  • Next message: Greg Roberts: "Optical 12 Dec 2012 Part 2"

    Op 13-12-2012 1:09, Mal Ninnes schreef:
    > Hi Marco,
    > It's a Canon 600D with EF-S 18-55 IS II lens, which I only got just recently.
    > Still getting the hang of night-time shots, as I'm not an expert
    > photographer. I read the messages from yourself and Greg the other day and
    > took photos of my GPS app (on android) at the start and end of my session,
    > also taking into account the 16 leap seconds, and I've previously checked
    > this against the US navy time servers on the net. The Canon time was off
    > during last nights session by 4 seconds, which I corrected for as well.
    > Obviously with this setup, I can't get sub-second accuracy. But for a start,
    > I'm ok with it.
    Hi Mal,
    It is perfectly possible to get subsecond accuracy with a DSLR (it is what I 
    do), but it involves carefull calibration.
    Note that the time display of a GPS device is seldom quite accurate (while GPS 
    time in itself is very accurate, this is not the case for the time in the 
    display on most GPS devices. Unless they are specifically build for timing 
    accuracy, such as GPS video time inserters). The display of my Garmin GPS can be 
    off by more than a second. This is because sending positional data to the 
    display gets priority over time information in internal processing in these devices.
    The best time source to use with a DSLR actually is a radio-controlled clock, at 
    least if you avoid the Cresta brand clocks (they are inaccurate, I have found). 
    Oregon Scientific is a good brand. Avoid too fancy clocks with many bells and 
    whistles, as you never know how detrimental those extra bells and whistles are 
    on the actual display accuracy. Force the radioclock to synchronise shortly 
    before your observing session (e.g. by taking the batteries out and then put 
    them in agan).
    Don't bother with your camera EXIF time: use the radio-controlled clock to try 
    to trigger your camera at an exact time and write those times down. Target a 
    number of unclassified satellites in a controlled, not too low orbit (e.g. 
    Iridiums) and map the offsets in delta T of your obtained positions to predicted 
    positions (Scott Campbell's software is very useful for that). That will give 
    you your calibration values.
    For satellite photography, ideally you would want a fast prime (= fixed focal 
    length) lens rather than a slow and optically mediocre zoom like your EF-S 18-55 
    (if your lens is the kit-lens, you'd want to replace that one anyway). On the 
    second hand market you can get a fast EF 50mm for very reasonable prices: try to 
    get one and use it with an F settings no larger than 2.8. The larger your lens 
    opening, the fainter objects you will be able to capture. For a given focal 
    length, an F2.8 or F1.8 hence is advantageous over an F4.5 or F5.3: your object 
    will appear brighter on the image.
    I noted that your picture was slightly out of focus. The best way to focus is to 
    put your lens on "manual", then put the "live view" of your camera display on. 
    Point to a bright star, zoom in on it on the display (not with the lens itself! 
    Just on the display with the "+" button) and focus manually untill the star is 
    pinpoint. Take a test image to see whether focus is indeed sharp.
    Hope these hints are helpful!
    - Marco
    Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
    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:
    Twitter: @Marco_Langbroek
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