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Della,
Here’s some general information below about Calibration frames
Calibration Frames
What are Calibration Frames ?
Calibration frames are specific photos or images captured in addition to the light frames which are stacked with your light frames to improve the quality of your final image
Types of Calibration Frames
Calibration frames include Darks, Flats , Dark Flats and Bias frames
Darks
Darks are frames which record the electronic noise or thermal noise your camera produces during an exposure. Darks will also eliminate stuck pixels in an image which can be both hot and cold pixels.
Darks are captured with the lens cap or lid fitted to the end of the telescope and are the same exposure length, same ISO or same Gain and same camera temperature as your light frames.
Usually 20 to 50 Darks are sufficient for Calibration purposes
Flats
Flat frames are used to create a uniform evenly illuminated or flat field across your image.
Flats help in minimising vignetting, dust donuts and other artifacts or anomalies in your image.
Flats are usually captured using a white t shirt stretch over the end of the telescopes OTA and pointed to an evenly illuminated light source like the early morning sky ( sky flats ) or a dimmer able Led light panel ( light flats ) Flat frames are usually short in exposure time ( 0.5 sec to 15 sec ) and must have the same focus and ISO or Gain settings on your camera as your light frames. Flats may differ from camera to camera but generally should be exposed 1/3 to 1/2 way across on your Histogram. Generally 20 to 40 Flat frames should be sufficient for Calibration purposes.
Bias Frames
Bias frames are used to reduce noise in your image in particular dark fixed pattern noise.
Bias frames are captured with the lens cap or lid on the end of the telescope with the shortest possible exposure available from your camera ( <1 sec ) Bias frames must have the same camera temperature, ISO and Gain settings as your light frames.
Generally 50 to 100 Bias frames should be sufficient for Calibration purposes.
Dark Flats
Dark Flat frames are captured to calibrate your Flat frames and reduce noise.They are captured with the lens cap or lid on the end of the telescope. Dark flats must have the same camera temperature, focus , ISO or Gain as your light frames but most importantly the same exposure time as your Flat frames. Generally the quantity of Dark flats should match your Flat frames to keep things simple.
Stacking Calibration Frames
Many cameras including various DSLR , cooled CMOS OSC and Mono cameras require different Calibration stacking requirements. Calibration frames from cameras sometimes produce better images after stacking from different combinations but in every case Flats frames must be used to create an evenly illuminated field.
Examples:
Lights ,Flats, Darks
Lights , Flats , Dark Flats
Lights , Flats , Bias
Lights, Flats , Darks , Bias
It’s best to research your camera type on forums or from the manufacturer to find out what Calibration frames work best.
The quantity of Calibration frames stated above should be used as a guide only. Final required quantities of Calibration frames are based on individual equipment requirements and outcomes
Stacking Calibration Frames
There are many Astro software programs on the market available for stacking your lights with calibration frames.
Deep Sky Stacker is very good stacking software and popular worldwide. It’s also open sourced so it’s a free download. There are many other good stacking programs to choose from like Astro Pixel Processor , PixInsight , Siril but most require purchasing.
Clear Skies
Martin
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