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Margaret Watson LRPS AFIAP


CCD Calculator
Select a CCD camera and telescope (or enter an actual focal length and ratio of your telescope) from the dropdown lists below. If you enter an actual focal length and ratio then any selected telescope will be ignored and the extender/reducer factor will be applied to this entered value. You may also change the binning to see the effect this has on pixel resolution.
Click Calculate and the pixel resolution and field of view will be displayed below.
The Sub-Exposure value, if displayed, is for guidance only and depends upon your local sky conditions and several other factors. Use this value as a starting point and experiment to determine the best value for your local conditions. For a more in depth explanation and method refere to Steve Cannistra's article on "Signal to Noise Ratio and the Subexposure Duration".
CCD Camera
or Enter User Defined Focal Length
and User Defined Focal Ratio
Pixel Binning


Colour Balancing Of RGB Images Using G2 Stars For Calibration
This selects suitable stars from your location with the appropiate time zone offset. Enter the desired time you expect to make the exposures or click Reset Local Time for the current local time.
To reduce the number of stars listed select the minimum (Vmin) and maximum (Vmax) V brightness of the stars, and also select stars by meridian transit, which can be in the eastern sky (Before meridian transit) or western sky (After meridian transit)
Click Select Stars to list all stars against the selection criterior. Your settings will be saved in a cookie on your local machine for when you return.
Local Date   
Local Time
Time Zone Offset
UT Date and Time
Vmin    Vmax    All stars  Before meridian transit  After meridian transit    

To calculate the exposure ratios at zenith input the average height of the star and the 3 ADU values derived from about 30 combined exposures which fully calibrated.
Clicking Save This Dataset will save the ratios in a cookie on your local machine for you to use in the Image Colour Balance tab. You will be prompted for an identifying name, make this so you can identify the dataset for a camera, filter set, and telescope i.e. Atik383_Baader_FSQ85.
Height of G2 star  °
ChannelMeasured ADU ValueExposure ratio at Zenith

To colour balance an image select the appropiate dataset (or enter the ratios at zenith determined in G2 Star Measurements tab manually) and enter the average height of the exposed object, the number of Red exposures and all channel exposure durations.
The factors calculated from the parameters eneterd should be applied when you combine the RGB image as Filter Multiplication Factor for each channel.
Red ratio at zenith    
Green ratio at zenith
Blue ratio at zenith
Average height of object during exposure  °
Number of red exposures
Red single exposure time  s
Green single exposure time  s
Blue single exposure time  s
ChannelOptimum ExposuresFilter Factor

This lists your saved datasets. You can delete any that are out of date or you no longer require. To delete a dataset check the corresponding control and click Delete checked Datasets
ControlDataset IDDate CreatedRed RatioGreen RatioBlue Ratio

This calculator was inspired by the Excel Spreadsheet solution developed by Bernhard Hubl which itself was based on the Color Imaging chapter of The Handbook of Astronomical Image Processing, written by Richard Berry and James Burnel.

If you would like me to add any other CCD's or telescopes, or additional facilities to these calculators,  then just fill in a request below.
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