Hmm. We should be able to work this out.
The first pic posted DOES claim to be a composite of two different images, altered to compensate for exposure. Tthe others, which show the moon and
planets at similar brightness don't say anything about being composites.
As a rule, light emitted from an object falls off in intensity in proportion to the square of the distance from that light. this actually refers to a
point light source emmitting in all directions, like a star or lightbulb for example. It's called the Inverse Square Law.
Better explanation here!!
The other thing you need to know about is camera dynamic range.
In photography terms, one "stop" refers to a doubling or halving of the of light light being allowed into the camera.
So as to get a correct exposure the photographer adjusts the aperture or the shutter time. If there was half the light available, he/she could double
the exposure time to compensate. They would have then have increased the exposure by 1 F-stop.
F-stops therefore refer to light intensity and are effectively a logarithmic scale, with each increase of 1 stop corresponding to a doubling of
intensity or "brightness".
The dynamic range of a camera, i.e the difference between the darkest detail it can pick out above black, and the lightest detail in can pick up below
white, is measured in F-stops. Both digital and film cameras have maximum dynamic ranges of around 8-9 F-stops. (our eyes can detect around 16 stops,
9 F - Stops = a ratio of 1:640 between the brightness(light intensity) of the darkest visible detail in comparison to the lightest detail, that could
be captured in a single "shot".
Now in these photos the moon and planets are not at the darkest and lightest ends of the dynamic range, so the ratio of brightness between them must
have been somewhat less than 640:1 . In fact they only look a couple of stops apart to me, but since we don't know what kind of contrast and gamma
adjutsments have been made, I going to go for a VERY generous, 8 stops in difference, and therefore a maximum intensity ratio of 320:1
Therefore, to tell if the moon and planets COULD have been captured in a single shot we need to figure out if the actual intensity of the light that
would have been reflected by the moon and the planet, could have a ratio LESS than 320:1
I'm afraid that's where my maths ability gives way, it should at least be possible to figure out a theoretical minimum ratio between the two bodies
brightnesses. you would just need to know:
a/ the distances involved. (sun>moon>earth and sun>saturn>earth)
b/ the rough reflectance of the moon and saturn.
Any mathematicians able to help here?
[edit on 1-8-2004 by muppet]