Re: resoluton of observable objects, camera color balance, observing satellites is fun (or maybe just addictive)

From: Robert Reeves (
Date: Sun May 29 2011 - 02:41:09 UTC

  • Next message: Thierry Legault: "Re: resoluton of observable objects, camera color balance, observing satellites is fun (or maybe just addictive)"

    Well said George.
    I'm in agreement with what you have said.
    I don't post often here, but have been observing satellites since Sputnik 3. 
    I have also written two books about digital astrophotography, one dealing 
    specifically with webcam-style work like Ralph uses, and thus look at his 
    work with admiration and often forward his amazing ISS images to the 
    astronaut office in Houston.
    As a long-time astro imager, I see nothing to tell me that the image of a 
    free-loating astronaut outside ISS was not possible under the right 
    circumstances.  The oft quoted Dawes Limit for telescope aperture pertains 
    only to point sources and visual work.  It really doesn't apply to linear 
    objects and images processed from multiple frames via RegiStax.  We can 
    routinely push digital imaging resolution beyond the Dawes Limit as long as 
    things go your way, like achieving best focus with properly collimated 
    optics and Mother Nature blesses you with great seeing.  Some of the modern 
    earth-based lunar imaging rivals the Lunar Orbiter images of the 1960's.
    I had predicted for some time to my astronaut friend Don Pettit (launches 
    from Kazakhstan this November) that it was just a matter of time before 
    someone bags an image showing a free floating EVA.  I have no doubt Ralph 
    did it and I hope he continues to do so.  I would love to see such an 
    earth-based EVA image of someone I actually knew!
    Robert Reeves            San Antonio, Texas
    Planet 26591
    ----- Original Message ----- 
    From: "George Roberts" <>
    To: <>
    Sent: Saturday, May 28, 2011 12:23 PM
    Subject: resoluton of observable objects, camera color balance,observing 
    satellites is fun (or maybe just addictive)
    > The goal here by everyone including Thierry and Ralph isn't to whine,
    > complain, belittle, show off, brag, lie, or deceive (well maybe a little
    > bragging).
    > The goal here is to observe satellites, share observations, and try to 
    > draw
    > conclusions from those observations.  When Ted asks y'all to share more
    > please don't get mad, you don't have to share but we would love it if you
    > did.
    > For example I've been tempted to discuss Thierry's conclusion of 
    > resolution
    > limits and the ability to see something 2 meters tall using Ralph's
    > equipment (an astronaut).
    > Although I partly agree with Thierry's points I think he has a
    > misunderstanding.  That white spot on Ralph's image indeed might  (might!)
    > be an astronaut.  Thierry hasn't yet convinced me otherwise despite his
    > educational composite of an astronaut to scale against the ISS.
    > I think a simple example will illustrate my point.
    > Currently Ralph's equipment is insufficient to image the Lunar Modules 
    > left
    > behind by Apollo missions on the moon (hopefully this will change, lol!).
    > There is a commonly used equation from Rayleigh that draws conclusions 
    > about
    > resolution that only needs to take into account aperture.  I beleive this
    > formula was originally co-opted for the specific case of observing binary
    > stars of equal brightness.  The formula  doesn't necessarily apply to this
    > situation.
    > If I put a laser next to that lunar module, make it bright enough (maybe a
    > million watts? a billion?) and shine it back at Ralph's telescope, Ralph
    > will see a tiny dot on the moon.  That dot should be the size of a star or
    > airy disk image of a point source.  So clearly it is possible to image
    > something "beyond the possible resolution" of a given set of equipment. 
    > The
    > key here is contrast.  The object imaged needs to be so bright that even 
    > if
    > it is only one inch across on the surface of the moon, it is brighter than
    > all the reflected light from the portion of the moon at Ralph's 
    > equipment's
    > "imaging limit".  So if for example the limiting resolution on the moon is
    > an area 1 mile across, then the laser needs to noticeably brighten 1 
    > square
    > mile of lit up moon as seen from the earth.  In the shadowed part of the
    > moon, the energy needed is much less.
    > Similarly, an astronaut working on the ISS, if lit up significantly 
    > brighter
    > than the area around him (sunlit astronaut, midnight dark stuff around 
    > him)
    > might be visible even if he is beyond the resolution limit of Ralph's
    > equipment.  Now the shape of that astronaut is probably noise, but one 
    > might
    > be correct in guessing that a certain region of the image is a particular
    > astronaut (or it might be a nearby part of the ISS also in bright sunlight
    > or it might be both objects merged into one).  Careful analysis of the 3D
    > shape of the ISS, the position of the arm and astronaut, and how sunlight
    > would fall on different parts of these objects might provide strong 
    > evidence
    > one way or the other.  Ralph did some of this analysis.  I don't think
    > Thierry did.  I'd love to see someone create a 3D model of the ISS and 
    > then
    > put a light source exactly the same angle as when Ralph photographed it 
    > and
    > then look at it from the angle Ralph did.  But this is a ton of work.  I
    > don't know if anyone will ever do this although I've heard there is 
    > software
    > that does this already.  One would need to know within a few seconds when
    > the image was taken and where Ralph was.  Ralph only included the time to
    > the nearest minute but that might be good enough as you can probably infer
    > the time and light angle by comparing 3D model lighting with Ralph's image
    > if you have software that allows you to quickly change the light source
    > position and see results in real time.
    > But we have to be careful about the "canals on mars" phenomena which 
    > fooled
    > some very smart people!  Like Percival Lowell:
    > Regarding the color of the nanosail, Thierry makes some okay and some not
    > okay points.  I'm particularly interested in this claim about color 
    > balance
    > for certain cameras in low light conditions and I would think Ralph would 
    > be
    > delighted to do a few controlled tests.  If someone accused my photos of
    > having bad color balance I wouldn't get pissed off at the person, I would
    > thank them (yes, really - I've learned to thank people for advice although
    > when I was younger...) and asked that person to help me set up some
    > experiments.  If one used the same camera indoors at night - light up some
    > very very small angular objects with a very dark background in a room. 
    > See
    > if the camera gets it's color balance out of wack or if it indeed has just
    > as good color balance with dark backgrounds as with light backgrounds.
    > There might be some auto color balance setting (software) in the camera 
    > that
    > gets confused by large "black" areas or quite likely Thierry could be 
    > wrong.
    > An experiment could settle this.  Ideally I'd like to see Thierry design 
    > the
    > experiments and Ralph do them over and over until Thierry is satisfied 
    > that
    > Ralph's images don't have color error introduced by the camera color 
    > balance
    > or Ralph finds a setting on his camera that disables color correction.
    > Ralph and Thierry should be best friends excited on working on this 
    > project
    > together!  Even if only by phone and email.
    > I think Thierry and Ralph are contributing great stuff here and I wish
    > people would bask in this great, interesting jumble of thoughts and
    > experiments and results and not feel personally attacked.  We are talking
    > about *ideas* here.  We aren't rooting for teams like in sports.  With 
    > ideas
    > the best and correct idea *always* wins.  And all the people win also.  We
    > all lose if Thierry claims the pictuers are bad and Ralph replies with 
    > "they
    > speak for themselves".  In that case I don't learn much.  Ralph and 
    > Thierry
    > aren't fighting each other.  Or they shouldn't think of it that way.  They
    > just have a disagreement about conclusions.  Thierry would like to see 
    > more
    > data.  Ralph doesn't want to supply it.  Regardless I think Thierry brings
    > up interesting points, some right and some wrong.  And Ralph also brings 
    > up
    > some interesting points - especially the concept that it might be possible
    > to photograph something as small as a human on the ISS.  What an amazing
    > feat if this really is possible!  It's great to try to push our technology
    > to new limits.
    > - George Roberts
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