Calibration Frames
Calibration frames remove and clean up certain artefacts from your stacked images.
Lights: These are the “normal” exposures of your target.
Darks: Remove thermal noise.
Flats: Remove vignetting and dust bunnies on the lens/filter/sensor.
Bias: These frames remove read out noise.
These exposures need to be added to your stacking programme along with your light frames. Below is a guide on each frame type:
Dark Calibration Frames
•Cover the front of the telescope/lens with the cap
•Dark frames are the same exposure length as your main images
•Same ISO setting as the light frames
•Same temperature as light frames
•Usually take as many darks as lights
•Don’t need to be taken every session - you can create dark libraries and reuse
Flat Calibration Frames
•With the cap off place a bright, even light source over your scope like a light-box. Alternatively, cover the front with a white cloth like a T-shirt and download a white screen app for your phone or tablet and hold it over the T-shirt. Keep all filters/reducers/diagonals in place for flat frames. 15 - 20 exposures. Software like BackYardEOS or APT will automate the taking of flats, which is handy.
•Put your camera in to AV mode
•Same ISO setting as the light frames
•Same focus as light frames (IMPORTANT) This is very important as this eliminates dust and vignetting. Changing the focus or camera orientation before taking flats will not remove dust bunnies from your final image.
ALWAYS take after every target/session. If you change target always take flats before you refocus for the new target.
•Take between 15 and 20 exposures
•Take a few "test" exposures until you have the histogram curve to be towards the middle of the graph
Bias Calibration Frames
•Cover the front of the telescope/lens with the cap
•Fastest exposure your camera can take
•Same ISO setting as the light frames
•Temperature is not important so can be taken any time
•Take 50 - 100 Exposures (These are quick so it wont take long)
•Don’t need to be taken every session - you can create bias libraries and reuse
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