To create lower noise Milky Way images, I have tried image stacking with different number of images using DeepSkyStacker (it can be done with Adobe PhotoShop but I feel that DeepSkyStacker is easier to use and it is FREE). The result is promising when the number of stacked images goes beyond 9 which gives ~3 times signal-to-noise ratio (SNR). The camera used for all pictures here is OnePlus 3’s camera.
Here is the cropped portion of the Milky Way.
Below is comparison between different number of stacked images with DeepSkyStacker.
From the differences in noise level, I feel that 9 to 16 stacks of image is good enough to create a final Milky Way image with smartphone camera that matches the noise level of single exposure Milky Way image from entry level DSLRs.
Shooting
The shooting process could be troublesome as shutter triggering is a repetition process. Intervalometer app is an automated app to automate shutter triggering to ease the shooting process.
Intervalometer (Further detail on this app in this post)
Post-Processing
In DeepSkyStacker, “Open picture files” to import the images as Light frames and “Check all” to select all the images. To stack the images, select “Register checked pictures” and “OK” to start stacking. Default setting is usually good but not every time. If default setting doesn’t produce a good final stacked image (blurry stars), there are some tweaks in Register Settings to create a better stacked image.
1. Star detection threshold: Decreasing the threshold value will increase number of detected stars which means DSS will detect fainter stars. The number of detected stars should not be too high, 40 to 200 stars are good enough for aligning.
2. Set lower percentage of pictures for stacking to eliminate more bad pictures. This also reduces the number of images used for stacking and noise reduction will be less effective when the percentage is set too low.
I stacked twice in DeepSkyStacker, one with auto alignment, one with no alignment to stack foreground to achieve similar noise level with the sky. Both layers are then blended together in PhotoShop using masking tool and post-edited in Lightroom to create final images as below.
*drag the slider to view the difference
Single Exposure vs Stacked of 25 exposures with each 30 seconds, ISO 1000
Single Exposure vs Stacked of 9 exposures with each 30 seconds, ISO 1000
Single Exposure vs Stacked of 20 exposures with each 30 seconds, ISO1000
Single Exposure vs Stacked of 9 exposures with each 30 seconds, ISO3200
Single Exposure vs Stacked of 27 exposures with each 30 seconds, ISO3200
The last image above was taken in a place that is far from light polluted cities. The light pollution is minimal and therefore much more details can be recovered from the stacked image.
*Click to view the full resolution
