Glossary

Calibration Frames

updated: 2025-10-25

Calibration Frames are required to reduce effects resulting from your optical equipment (like vignetting), electronic noise like read out noise or pixel errors. Depending on the equipment or SW used there are different ways how calibration frames can be obtained. So called Master Calibration Frames are stacked images of a number of single calibration frames. 


Characteristics of master calibration frames


Calibration frames are required during the Calibration Process as shown below:


source: ...\Astro\StarlustDocs\Astro Image Processing Overview[CalibrationShort].

Calibration Process

source: ...\Astro\StarlustDocs\Astro Image Processing Overview[ImageCalibration]

Calibration Frame Dependencies

This graph shows the dependence of the various calibration frames on the different exposure parameters. While the light frames (blue) depend on all parameters (green), only certain properties are relevant for the pure calibration frames (red), which should also be reflected in the folder structure and file names.

source: ...\Astro\StarlustDocs\Astro Image Processing Overview[CalibrationDependencies]

Master Frame Organization

Organize your master frame folders e.g. like:


Master File Naming:


IMPORTANT: The name of a Flat Frame master file should always include the abbreviation of the filter used. This Must be set manually if no filter wheel is used. 

Examples: FILTER-NoFilter, FILTER-OLeN, FILTER-UHC2 or FILTER-NoFilter
Because color light frames from an ASIAIR OSC camera never contain any filter information, even if a filter has been used. The Master Flat Frames must therefore be renamed and the string _filter-NoFilter must be added somewhere in the filename. They also need to be converted from a .fit to a .xisf file in order to be accepted by the WBPP or FBPP batch pre-processing scripts in PixInsight.

Master File Naming Examples

Master Dark Calibration Frames

      • MasterDark_Stack20_180.0s_Bin1_2600MC_gain100_20250305-10.0C.fit
      • MasterDark_Stack20_30.0s_Bin1_FUXT3-16-55_ISO3200_20251015.xisf

Master Bias Calibration Frames

      • MasterBias_Stack50_1.0ms_Bin1_2600MM_gain100_20250219_-10C.xisf
      • MasterBias_Stack20_0.123ms_Bin1_FUXT3-16-55_ISO3200_20251015.xisf

Master Flat Calibration Frames

      • MasterFlat_TS600ASI2600CAA_2600MC_Filter-NoFilter_Bin1_gain100_-10.2C_20251027.xisf
      • MasterFlat_TS600ASI2600CAA_2600MC_filter-OLeN_Bin1_gain100_21.0C_20250304.xisf
      • MasterFlat_TS600ASI2600CAAx075_2600MC_filter-OLeN_Bin1_gain100_22.2C_20250824.xisf
      • MasterFlat_FUXT3FU135_FoL-135_FILTER-UVIR67_EXPOSURE-30.00s_BIN-1_ISO-800_6246x4170_CFA


Capturing Calibration frames

Dark Frames

Bias Frames

Flat Frames

Environment

Cover your camera: your camera or scope must be covered to block all light off the sensor

Cover your camera: your camera or scope must be covered to block all light off the sensor

Use a evenly-lit light source, e.g. twilight sky, laptop screen, LED light panel, light box, TV screen, a white T-shirt to cover your telescope  or similar.

Re-Usability

yes

yes

Should be taken during every imaging session because they depend on the alignment of the entire imaging train

Gain or ISO

same as light frames

same as light frames

same as light frames

No. of exposures

minimum of 20 frames

50 to 100 frames

same no. as light frames

Exposure time

same as light frames

as short as possible (e.g. 0.001s for CMOS cameras)

optimal exposure time, no over or under exposure (different form light frames)


Hint: Master calibration frames can be automatically captured and stacked with the  Live Stacking function of  ASIAIR.

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