Create Calibration Master

Calibration Masters are high quality Dark, Flat, and Bias frames that are used to remove camera and scope artifacts from the images. Several individual frames are used to create a master.

Click(New Job) to open the Select Task form:

Press the Create Calibration Master button.

If you have not yet created a profile then you will be prompted to do so. Otherwise the following form will appear:

A flat frame is an exposure of a uniformly lit area (sky or screen) that is used to compensate for illumination variations such as vignette, dust on optical surfaces, and peculiarities of the sensor. Stacking individual flat frames produces a master flat that has superior signal-to-noise for improved effectiveness.

A dark frame is an exposure of nothing (shutter closed) that matches the raw images in length and temperature (as much as possible). Dark frames are use to remove the effects of “dark current”, which is an uneven build-up of non-photonic electrons. A dark frame contains noise that can be diminished by creating a “master” via stacking many dark frames.

A bias frame is a short dark frame that represents the ground state of the detector. Bias frames are used for adaptive dark subtraction and are convenient to use for dark-subtracting flats (flat exps are generally so bright and short to contain any significant dark current).

Create Flat Master

A “flat frame” is an exposure of a uniformly lit area (sky or screen) that is used to compensate for illumination variations such as vignette, dust on optical surfaces, and peculiarities of the sensor. Stacking individual flat frames produces a master flat that has superior signal-to-noise for improved effectiveness.

The above fields are only used to construct a file name, which can be overridden later.

Press OK:

Select flat frames.

The next question is important:

For a flat to correctly calibrate an image, it is necessary for the software to know the “zero point” of the flat. There are two ways to accomplish this: dark-subtract the flat or enter the average bias level (measure the average DN of a short dark frame).

Most raw DSLR formats contain metadata that is used by Stacker Unlimited to pre-set the zero-point to zero, so unless you know otherwise, accept the default form.

Most raw CCD FITS files have a significant non-zero bias and it is advisable to use [dark or bias] subtraction or specify the average bias. If the flats are already dark-subtracted by other software then enter the software’s pedestal (often 100) for the average bias level.

Press OK:

Stacker Unlimited will suggest a file name and folder. To change either, click on the file name and specify a different mane and/or folder.

Press Run Now.

It may take a few seconds for the process to start. Note that the top toolbar has new controls and a viewer for the stack is automatically opened. Current process information and progress is reported on the bottom status-strip See Job Processor for details on the controls and information displayed. Upon completion the Reset button will become active and the status will report all of all frames processed:

The Master Flat file has been automatically saved (unless you unchecked the autosave box).

Create Dark Master

The above fields are currently only used for documentation and are not required. It is very useful to document these quantities. After filling in the texts, press OK:

Select all associated dark frames (they should all have the same exposure time and temperature).

Stacker Unlimited will suggest a file name and folder. To change either, click on the file name and specify a different mane and/or folder.

Create Bias Master

A bias frame is basically a short dark frame and thus the procedure is the same as described for Creating Dark Master above.