Re: Need inputs for shooting ISS solar transit

From: Sankaranarayanan K V (
Date: Thu Jan 23 2014 - 04:17:06 UTC

  • Next message: Thierry Legault: "Re: Need inputs for shooting ISS solar transit"

    Thank you very much, John, Marco, and Thierry and those who responded off
    list!  Appreciate all your help. I will do the required home work and be
    ready for my first attempt.
    Thierry, are you suggesting I use a German equatorial mount compared to a
    fixed tripod? I have a Sky Watcher NEQ6.
    On Thu, Jan 23, 2014 at 3:36 AM, Thierry Legault <>wrote:
    > Sankar,
    > 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!)
    > Regards
    > At 21:33 22/01/2014, Sankaranarayanan K V wrote:
    >> Hello:
    >> 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.
    >> Thanks!
    >> Regards
    >> Sankar
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