Second edit of my recent star trails image pulling out the lightest of the frames as the sky changed to twilight. Processing this in Photoshop I am using layers and the lighten blending – so the blue hour version drops quite a few stars as the sky brightens and the software stacks the images to create the composite. I like both versions – the darker for the sheer number of stars that have been captured and the lighter version for the play of the lightening sky against the structure of the bridge.
