When should I shoot dark frames for long tracked astrophotography exposures?
Asked 7/22/2020
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I shoot tracked astrophotography exposures around 15 minutes each at ISO 320, usually 5–8 frames per night, and then stack them to reduce noise. I’d like to start using dark frames in my workflow.
What’s the most practical way to capture dark frames for this kind of session? For example, should I alternate light frames and dark frames, or shoot all my light frames first and then take dark frames afterward?
If dark frames are useful here, should they match the full 15-minute exposure length? And if my total imaging time is limited because the Milky Way is only visible for a few hours, what’s a realistic approach?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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Shoot (15 minutes) x (However many frames you want) → manually shoot one dark frame (15 minutes). You can take a manual dark frame by putting a lens cap on the lens before taking the shot. You're done.
Now, use a stacking software that allows you to use a single manually shot dark frame to be applied to each frame
If your total shooting session lasts more than an hour or so, you could take a dark frame each hour or so and use each specific dark frame for the images you've taken between when you took the last dark frame and the most recent dark frame. Some stacking software will easily let you do this, others make you work more for it. You might need to create "sub stacks" for the images taken before each dark frame, then stack the separate results of each stack together.
Also, cover the viewfinder if it is a DSLR with an optical viewfinder. Sometimes minute amounts of light can leak around the edges of the mirror when it is up.
If you have a mirrorless camera with an EVF, you do not need to bother covering the EVF.
For more, please see:
What's the best way to deal with hot/stuck pixels in long exposure night photographs?
Why does my Canon 700D take so long processing when I take a long exposure?
Stack of 4 seconds exposure photos of Milky Way, how is it done?
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
5y ago
0
Generated from our catalog & community — verify before relying on it.
For best results, dark frames should match your light frames in key settings: same exposure time, ISO, and as close as possible to the same sensor temperature. So for 15-minute lights, use 15-minute darks—not 1-minute darks.
A practical approach is usually:
- shoot all or most of your light frames first
- then take one or more dark frames with the lens cap on
- apply those darks during stacking
If your session is fairly short, one matching dark frame can still be useful. If it runs longer than about an hour and the camera temperature may change, taking a new dark frame every hour or so is a reasonable compromise and you can apply each dark to the nearby light frames.
Alternating every light with a dark is usually inefficient when your available sky time is limited, because it cuts into time you could spend collecting actual image data.
So the realistic option for limited Milky Way time is: prioritize your light frames, then capture one or a few full-length dark frames afterward, or occasionally during the session if temperatures are changing a lot.
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