View single post by Robert
 Posted: Wed Nov 15th, 2017 14:50
Robert



Joined: Mon Apr 2nd, 2012
Location: South Lakeland, UK
Posts: 4066
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 Last Sunday, (12th November 2017) the sky was so clear I could not resist trying my hand at making some exposures of the Milky Way. Actually almost the entire sky! I had made two sets of star trails, so to try to make good use of the time while I was waiting for the Moon to rise, I pointed the lens vertically up. I couldn't tell at the time but I had the ground visible at each corner of the image in pretty much equal amounts. The 16mm fisheye is 180º across the corners. I also forgot to make a note of where North was.

o.O

I took about 30 exposures at f2.8 for 25 seconds at ISO 1600, at one minute intervals.

Using 'Starry Landscape Stacker', I experimented and using ten images, I stacked them. They were aligned perfectly by the software and that had the result of eliminating noise AND the pesky airplane trails. The software baulks at using images exposed over too great a time span because the earth rotation means shifting the alignment too far within the bounds of the preferred reference frame.

I should have also created a similar number of 'dark frames', exposures made at the same time, after the sky exposures with identical settings but with the lens cap on. The stacking software uses the dark frames to deal with dead and hot pixels, to exclude them from the calculations. I cheated! I put the D3 on my desk with the lens cap on and set it off making 30 exposures at the same settings as the original live exposures.

I had to alter my usual processing method, zero contrast and slight exposure adjustment is all that is recommended prior to stacking. After stacking, quite extreme adjustments are needed to extract the most from the image.

I should have used the mask to shield the corners from the sky processing but I think the bits in the corners would have been a messy distraction.



This is one of the original files with the contrast turned down prior to processing. I have rotated the final image 180º because I believe the original exposure orientation was with North at the bottom. So in the final image I think North is at the top, roughly.



____________________
Robert.