|Milky Way over The Watchman - Zion National Park, Utah. Light on mountain is light pollution from nearby Springdale city street lights ~ © Royce Bair|
|Simulated naked eye view|
|Histogram of a "naked eye" exposure|
The reason is because my camera is manually controlled to take the images at a longer exposure (typically 8 to 30 seconds, depending on the lens I'm using), so it gathers more light for its sensor than my eyes can. Also, the human eye has an iris aperture that is rated at about f/4.0, whereas my typical night photography lens is rated at f/2.8 or wider (letting in twice as much light to the sensor).
|Histogram of raw camera exposure|
|Raw camera exposure|
Post Production: The raw camera image has all the brightness and detail needed for a great photo, but it is flat or lacking in contrast. My final NightScape images are created in post production with very simple steps in Photoshop. All the stars are there in the camera's raw image, but a contrast gain in the sky is necessary to make them more apparent. My goal is give the same clarity you expect to see in an astronomical observatory (taken with a huge telescope) image, but with a wide-field view, coupled with an interesting landscape feature in the foreground — something the big telescopes cannot do!
|After adding curve adj.|
|"S" shaped adjustment curve|
|Slight color changes via Curves|
Final, minor color changes can be made in Photoshop's Curves to the the red, green, and blue channels (represented by the three diagonal colored lines). Be careful to not over do this — as a little color goes a long way. The final coloration depends on what you remember seeing in the sky that night.
Adjusting the landscape. The final step is to use the same saved sky selection (channel) and inverse it so that it is now selecting the mountains, instead of the sky. Once this is done, another Adjustment Layer (you can use "Levels", or "Curves", but Curves is more powerful) is created from that selection in order to change the color of the sodium vapor lights (coming about a mile away from Springdale city) —so that The Watchman mountain is a more pleasing "red rock" sandstone color.
|Histogram after all adjustments|
Compare: In the image below you can quickly compare the differences between the "naked eye" simulation, the "raw camera" exposure, the "S"-curve adjustment, and the final image —with the extended tonal range of its histogram.
|Click to enlarge.|
|Click to enlarge|