Terrestrial and Celestial Transport
04/08/18The International Space Station passes over the Prince of Wales Bridge. This image is a montage of 20 exposures of 10 seconds each at F/4 and ISO 800, all identical in composition, capturing the trail of the ISS as it moves from west to south across the sky. Because the ISS is moving, its brightness depends on aperture and ISO but not shutter speed. Hence by reducing the length of each exposure, I was able to make the bridge darker while maintaining the brightness of the ISS to balance the image. The exposure I used was the maximum I could while not blowing the highlights in the bridge. In processing I pushed the exposure of the whole image by +1 stop and then held back the exposure of the bridge using a virtual -1 stop ND grad. I combined the 20 frames as layers in Photoshop. Because the sky got darker between the first and last frame (3 minutes 20 seconds apart) I blended the 20 frames using the Lighten mode and then overlaid the ISS trail onto the background of the first (lightest) image, so as to show Jupiter (towards the left, between the bridge and the ISS) and the stars as points rather than trails. It is a pity there some murk over Newport that obscures the western end of the ISS trail; I was hoping to see the ISS rise between the bridge pillars.