I drove through Oregon last week and took some night sky photos. These first two are from Indian Mary park in southern Oregon, along the banks of the Rogue River:
I shot this photo of the Milky Way on a tripod near our camp site. I used my Canon 70d at 15mm, wide open for 30 seconds at ISO 6400. Due to the rotation of the Earth, when shooting night skies your longest possible shutter speed is constrained by a function of your focal length.
The rule of thumb for calculating your maximum possible exposure time is 500 divided by your focal length if you have a full frame sensor, or 300 divided by your focal length for cropped sensors (as discussed at length in this excellent article. In my case, 300 / 15mm = 20 seconds, but I cheated a little and used a 30 second shutter speed to get a brighter photo. The trade-off is the subtly oblong star trails.
Here’s another night sky shot of the starry sky and the trees surrounding our camp site:
We were in Portland on July 31, the night of the blue moon. I shot this photo on a tripod from the family’s front yard in east Portland, 300mm for 1/500 sec at f/8 and ISO 400:
