Re: Re: Awesome ISS photos!!!

From: Anthony Ayiomamitis (
Date: Tue Jun 12 2001 - 15:33:23 PDT

  • Next message: Anthony Ayiomamitis: "Iridium flare across the lunar surface"

    > > > As for dark satellites silhouetted against a bright(er) moon, it
    > needs
    > very
    > > > high contrast, and I can not imagine it being photographed,
    > because the
    > > > satellite obscures such a small area for a short (?) interval on
    > each
    > frame.
    > >
    > > My philosophy here (and this is where my failed attempts are
    > concentrated)
    > is
    > > that with a 1- to 2-second pass across the lunar surface, there
    > should be
    > ample
    > > time for acquisition and photography. The transit on Thursday is
    > good in
    > the
    > > sense that the transitting satellite (mag +4.8) which travel across
    > both
    > the
    > > dark and illuminated parts which is an opportunity for training my
    > eye on
    > what
    > > to expect across the two types of backgrounds.
    > >
    Hi Bjoern,
    > But the eye is different from film and CCD. If you have 600 pixels
    > across
        No argument from me on this one. In fact, I would say that film is
    the best recording device between the three. However, the problem with
    film is that you cannot keep shooting continuously (similar to video). I
    realize that we have automatic winders for cameras (I have these myself)
    that can get you around 7 frames per second but that means that you will
    go through a 24-exp roll in just over three seconds. A 36-exp roll is
    gone in five seconds.
        In contrast, with a CCD, you can record to your heart's content
    (limited by your hard disk space). However, CCD is restricted to longer
    exposures where we accumulate photons rather than trying to "freeze
    time" as we do with film emulsion.
        Either way we have a dilemma here and I fail to see a way out of it.
    > the Moon, each one is roughly 6*6 km.
    > At 750 km range, that is 12*12 m. So, even if the satellite has an
    > effective
    > albedo five times the Moon's, it would need 28 sq.m. to match its
    > intensity.
        An area of 28 sq m is something that I can live with (for now)  as
    we have at least 40 satellites  whose minimum area is 30 sq m or greater
    (this is based on memory from some number crunching I did a couple of
    months ago).
    > And a dark satellite of 6*6 m would only remove ~25% of the Moon's
    > light
    > during 1/600 s. - how long is your camera's exposure time/frame ?
        I base my proposed exposures on the phase of the moon as I am
    looking for a silhouette image cast by the satellite against the lunar
    surface. I do not want to determine the exposure on the basis of the
    satellite as any overexposure of the lunar surface will not only destroy
    the esthetics of the image but it may/should destroy the silhouette of
    the satellite as well.
        The maximum magnitude of the moon is -12.7 (full moon). I may be
    wrong but I seem to recall something like -8 mag for a very young
    crescent moon. Therefore, I must give the moon priority when
    establishing exposure settings since it represents the overwhelming
    light source.
         My suspicion is that one must use very high magnification so as to
    concentrate on a small physical area of the lunar surface and to choose
    this area with as much precision as possible which will coincide,
    hopefully, with the transitting satellite. This gets back to your
    analysis above regarding pixel coverage. However, this leads to a
    potential conflict ... higher magnification will mean a slower exposure
    but the much smaller field of view will require a faster exposure than a
    wider field of view so as to capture the transitting satellite without
    blurring ... two opposing forces at work.
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