Thu Jul 06, 2017 8:05 am
I can see that the longer "fl" requires a shorter exposure and thus appears as a divisor in the formula.Take out the star trails
The rotation of the Earth will make Orion appear to move slowly from east to west. The shorter the focal length of your camera lens, the longer the exposure you can get away with before you start getting star trails in your image. The formula for working out how long you’ve got is
Time (seconds) = 1000 / (fl x cosD)
where fl = lens’s focal length (mm) and D = declination (degrees). Assume D is 0° for Orion.
Thu Jul 06, 2017 3:34 pm
Thu Jul 06, 2017 5:54 pm
Thu Jul 06, 2017 8:52 pm
Tue Jul 11, 2017 11:32 pm
andrewt wrote:Are you agreeing that the Sky at Night article from 2008 is wrong?
Following on from that, we could have an angle of view centred on the pole of around 20degrees, where out at the corners of the field of view (for that lens) one would use the equation with Cos D using 10degrees giving your modifier = 0.98, when the corners of the FoV are near the pole.
Sun Jul 16, 2017 10:25 am
Thu Aug 03, 2017 10:46 pm