> > > 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.
Anthony.
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