Astro in Iso
For many of us with our movements restricted due to COVID-19, it’s a perfect time to develop our knowledge, refine our skills or even try something new. I have the urge to continue shooting images, and continue to practice in areas such as macro photography, working on my processing workflow and also refining my astrophotography techniques (when the weather permits). So last night was my time for astro, as a bonus I decided to share my workflow and approach to this genre, so here we go.
Clear skies are definitely beneficial for practicing astro, and light pollution does affect the results, but as long as stars are visible it’s fine for practicing purposes. From where I live there is some light pollution visible, but I find shooting upwards helps (maybe I’m in a dark patch or I’m just shooting through less of the light reflecting atmosphere).
Last night I decided to start by testing different lenses to see how they perform in capturing the night sky. For this test I used the Fujifilm X-T3 for the body and changed between lenses from the very wide Laowa 9mm f/2.8 (Fuji X-mount) to the not-so-wide Zuiko 135mm f/2.8 (Olympus OM-mount) with a focal reducer attached.
As for settings I calculated them to suit the lens, working with the different focal lengths and apertures.
Aperture - I decided to shoot with the aperture wide open for every lens, this generally isn’t where lenses perform the best, but it’s a good starting point for astro.
Shutterspeed - I wanted to keep the stars sharp without any trailing, I’ve found following the rule of 600 (also known as the rule of 500, or any other number that you find that works for you!) works best for determining my shutterspeed. For the calculation simply divide 600 by the product of the focal length and crop factor, which resulted in the shutterspeeds in the table to the right.
ISO - This wasn’t really calculated or kept consistent, just estimated to keep the exposure within an acceptable range.
White balance - For astro I always set it a custom 4000K, this is just to keep the images looking consistent on the back of the camera. I can further adjust this later in post-processing when shooting in the RAW format.
I turn on the 2 second timer which reduces camera shake and switch the camera to continuous shooting, by shooting in continuous the camera will capture a set of 5 consecutive frames rather than just one, which will become beneficial in the processing stage.
Once the camera is set up on the tripod and the exposure is set, I switch the camera to manual focus, point the camera to a bright star, magnify the preview to the max, and focus the lens to ensure stars are displayed as sharp points. I then re-frame the shot and press go.
Now to the image processing, first up, as with all photos is copying and backing up those precious image files! Certainly a step not to skip!
Next, importing the files into the preferred editing software, I use Capture One Pro 20, which I’m still learning especially during this time. At this stage I apply lens corrections, tweak the exposure, adjust the white balance and copy those adjustments to all 5 images from each lens. All images are then exported as TIFFs.
The 5 TIFF files from each set are then imported as a stack into Photoshop, where layers are auto-aligned and converted into a smart object. I then change the stacking of the smart object to ‘mean’, this process takes the average of every pixel within the stack and in doing so averages out the noise, leaving much cleaner files. The stack is then exported as another TIFF (or PSD) file.
Finally the new clean TIFF is re-imported into Capture One to complete the edit. For the above images, it was simply adding contrast and a little saturation, structure and clarity, with tweaking exposure, brightness, highlights, shadows and white balance to taste. I find it easy to over-process images of the night sky, so I try to stay away from local adjustments and use the saturation and clarity adjustments sparingly. That’s it! That completes the processing and they’re ready to export!
Looking back at these images, I’m surprised at how well the lenses performed. The Laowa 9mm does seem to display some radial colour shifts and had the largest light fall-off towards the edges, the Fujifilm 16mm follows in both aspects but has an overall much better performance. The 9, 16, 27 and 35 all show some softness towards the edges, so stopping the aperture down may be beneficial, but that is for another night. Overall, I find all lenses performed at an acceptable quality and would pick to focal length to match the landscape.
So if you’ve made it this far, thank you! You probably have a camera with manual settings, so charge up a battery, grab a tripod and practice some night sky stuff. If you already shoot astro, how does your process differ? Any suggestions to add?