by Joe Stieber » Sun Apr 24, 2016 7:00 pm
DavidLeodis wrote:The time given in the Exif data also confused me as the explanation (and in the caption to the image brought up through the 'the dreamlike scene' link) it states "A waning crescent moon, the emerging morning twilight" so thus not p.m. I find it adds interest to know at least the local date/time when an image was taken so I wonder what was the definite date/time?
Based on the moon's position, I'm still pretty sure it was taken on the morning of March 4, 2016, but the more I think about it, the more I suspect it was closer to 6 am local time. That would put it near the start of civil twilight. The brighter twilight then would provide the illumination needed to show the foreground canyon. I suppose the trick is to find the balance between enough twilight for the foreground, but not so much as to wipe out the background sky, which is already compromised a bit by the moon. Most likely, a number of exposures were taken starting before the onset of twilight. Then it's a matter of going through dozens of pictures to find the best one.
I have a Canon 6D too, and it has a built-in GPS which can update the camera's clock, if the GPS is activated and it's set to do the update. This, of course, would provide an accurate time stamp. However, I have found (as have others) that when the internal GPS is activated, even if the camera is switched off, the battery runs down in a few days (a quirk of the 6D, which is otherwise a fine camera). Therefore, one normally turns the GPS off when not using it, and back on when using it -- but of course, we all forget sometimes. However, even allowing that camera clocks (without GPS assist) are not all that precise, being 12 hours off would be an unusually large error for simple clock drift. Since Tafreshi apparently travels a lot, perhaps it was inadvertently still set to some distant time zone. I know a guy who travels a lot, so he sets his camera clock to UT to avoid the problem of constantly re-setting it for different local times, or having the wrong local time. It would indeed be interesting to learn what happened with the camera's time, as well as what the actual local time was for this picture.
BTW, some of my astronomy associates probably get tired of hearing me say it, but I'm always exhorting them to make sure their camera clocks are set correctly, especially at daylight time changes. In particular, even if they recently set it, I suggest they take a picture of a good clock page, such as the
Official NIST Time or the
USNO Master Clock, so they can go back and establish any offset between the EXIF time and what the reference clock shows in the image.
[quote="DavidLeodis"]The time given in the Exif data also confused me as the explanation (and in the caption to the image brought up through the 'the dreamlike scene' link) it states "A waning crescent moon, the emerging morning twilight" so thus not p.m. I find it adds interest to know at least the local date/time when an image was taken so I wonder what was the definite date/time?[/quote]
Based on the moon's position, I'm still pretty sure it was taken on the morning of March 4, 2016, but the more I think about it, the more I suspect it was closer to 6 am local time. That would put it near the start of civil twilight. The brighter twilight then would provide the illumination needed to show the foreground canyon. I suppose the trick is to find the balance between enough twilight for the foreground, but not so much as to wipe out the background sky, which is already compromised a bit by the moon. Most likely, a number of exposures were taken starting before the onset of twilight. Then it's a matter of going through dozens of pictures to find the best one.
I have a Canon 6D too, and it has a built-in GPS which can update the camera's clock, if the GPS is activated and it's set to do the update. This, of course, would provide an accurate time stamp. However, I have found (as have others) that when the internal GPS is activated, even if the camera is switched off, the battery runs down in a few days (a quirk of the 6D, which is otherwise a fine camera). Therefore, one normally turns the GPS off when not using it, and back on when using it -- but of course, we all forget sometimes. However, even allowing that camera clocks (without GPS assist) are not all that precise, being 12 hours off would be an unusually large error for simple clock drift. Since Tafreshi apparently travels a lot, perhaps it was inadvertently still set to some distant time zone. I know a guy who travels a lot, so he sets his camera clock to UT to avoid the problem of constantly re-setting it for different local times, or having the wrong local time. It would indeed be interesting to learn what happened with the camera's time, as well as what the actual local time was for this picture.
BTW, some of my astronomy associates probably get tired of hearing me say it, but I'm always exhorting them to make sure their camera clocks are set correctly, especially at daylight time changes. In particular, even if they recently set it, I suggest they take a picture of a good clock page, such as the [url=http://www.time.gov/]Official NIST Time[/url] or the [url=http://www.usno.navy.mil/USNO/time/display-clocks/simpletime]USNO Master Clock[/url], so they can go back and establish any offset between the EXIF time and what the reference clock shows in the image.