Re: Need inputs for shooting ISS solar transit

From: Thierry Legault (
Date: Thu Jan 23 2014 - 05:46:52 UTC

  • Next message: Russell Eberst: "2014JAN22.OBS"

    first of all, don't begin solar imaging by a 
    transit. You need to get skilled about solar imaging, including:
    - image enlargement by Barlow lens (at prime 
    focus the solar disk diameter is 4.5mm, much smaller than your sensor)
    - choice of exposure time. It depends on the 
    density of the filter and for the darker filters, 
    exposure time may be quite long (too long for the 
    speed of the ISS) or oblige you to increase ISO 
    setting (making images more noisy). Preferably 
    use Baader Astrosolar photo density sheet
    - focusing (live-view mode at maximum enlargement on sunspots or the limb)
    - either polar alignment of a German mount in 
    daylight or manual tracking of the Sun, depending on your equipment
    1. in two weeks, the centerline may move a lot. 
    Recalculating 2 days before gives a reasonable 
    precision for observation site search, and 
    recalculating a few hours before the event is necessary.
    3. run Calsky for several months and you'll have 
    an idea of the frequency for your area. Transits 
    are much more frequent around 50° latitude (top 
    of orbit) than in tropical or equatorial zones.
    With a fast card, your 60D is able to run at 5.3 
    fps for 16 frames in raw and 44 frames in jpeg:
    Raw mode offers larger range for processing, but 
    3 seconds is very (too!) short and you need a 
    very accurate time reference (common GPS don't 
    show a precision better than 1 second). For a 
    first transit, I would suggest video, especially 
    if you have to track the Sun manually. Resolution 
    will be lower (if atmospheric turbulence is not 
    too high, otherwise the result may not be very 
    different!) but you decrease the risks.
    PS: I have been in Bangalore during 2 weeks last 
    year for business. Nice stay (except traffic!)
    At 21:33 22/01/2014, Sankaranarayanan K V wrote:
    >CalSky predicts that there is going to be an ISS solar transit over
    >Bangalore, India (where I live) on 9th February. I am planning to attempt
    >photographing this. I have some questions related to this:
    >    1. Since the event is two weeks from now, in what ways can the center
    >    line and the predicted time change over time due to change in orbit
    >    parameters? Or in other words I am trying to estimate when I should start
    >    scouting for a good location on the center 
    > line? Would 2 weeks ahead be too
    >    early or should I wait till it's about 2 or 3 days prior to the event?
    >    2. I have seen Thierry Legault's amazing pictures. But very limited
    >    information on how to prepare and photograph such a short event. It would
    >    be great if any of you can provide suggestions and tips.
    >    3. How frequent are transit events for a given piece of area on Earth?
    >I have access to limited resources - I don't have a long focal length OTA
    >but just an 80mm f/6 refractor.  I have a DSLR body and am considering
    >using a long telephoto lens (with a converter). I have solar photographic
    >filter. Given this, should I shoot stills at high FPS around the transit
    >time or should I record a video and grab frames out of it to obtain good
    >stills? My 60D can shoot 5.3 fps but I need to test for how long it can do
    >without overrunning the buffer. It can also shoot a 60FPS video at 720P.
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