by Joe Stieber » Sun Aug 02, 2015 4:56 pm
PeteBataleck wrote:Why are there no stars visible ?
Today's APOD is obviously well exposed for a sunlit scene. Here on earth, which is essentially the same distance from the light source (the sun), the old rule-of-thumb from back in the days of film was that a sunlit scene with distinct shadows would be properly exposed by using a shutter speed that was the inverse of ASA film speed (now ISO) at f/16. For example, if they were using ASA 64 film, it would have been exposed approximately 1/60 second at f/16 (or some combination that gives the same exposure value, like 1/250 at f/8).
If you were to use a modern digital camera on a clear dark night here on earth, and take a picture of the sky with that exposure set manually, you'd get nothing. For comparison, to get a nice
snapshot of a well-populated star field from a dark site, I might use a typical exposure of 6 seconds at f/4, ISO 6400. That's a difference of more than 19 photo stops, or more than 500,000 times as much exposure as a standard daylight scene.
Quite simply, you can't capture dim stars with a brief exposure that works well for a bright daylight scene, whether you're on the earth or the moon, even if the moon doesn't have interference from a blue sky.
[quote="PeteBataleck"]Why are there no stars visible ?[/quote]
Today's APOD is obviously well exposed for a sunlit scene. Here on earth, which is essentially the same distance from the light source (the sun), the old rule-of-thumb from back in the days of film was that a sunlit scene with distinct shadows would be properly exposed by using a shutter speed that was the inverse of ASA film speed (now ISO) at f/16. For example, if they were using ASA 64 film, it would have been exposed approximately 1/60 second at f/16 (or some combination that gives the same exposure value, like 1/250 at f/8).
If you were to use a modern digital camera on a clear dark night here on earth, and take a picture of the sky with that exposure set manually, you'd get nothing. For comparison, to get a nice [i]snapshot[/i] of a well-populated star field from a dark site, I might use a typical exposure of 6 seconds at f/4, ISO 6400. That's a difference of more than 19 photo stops, or more than 500,000 times as much exposure as a standard daylight scene.
Quite simply, you can't capture dim stars with a brief exposure that works well for a bright daylight scene, whether you're on the earth or the moon, even if the moon doesn't have interference from a blue sky.