StarryCamera is the best camera app for a starry sky.
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# How to use
1. Mount your iphone on a tripod.
2. Choose shooting mode.
3. Choose ISO, Shutter Speed.
4. (Choose White Balance according to your preference)
5. Tap the shutter button.
# About 5 modes
Starry sky mode : Highlight bright stars, and increase contrast.
Star trails mode : Lighten blend mode for star trails.
Milky way mode : Increase contrast.
Night view mode : No image processing.
Lighten mode : Lighten blend mode. (for firefly, light trail, etc)
Improved image processing.
Removed resolution option from preference view.
Adjusted White Balance at fix mode.
Improved star trails mode (gradation).
Changed shutter speed at star trails mode.