Contents - Index


Wizards







G2V Calibration Wizard

CCDAutoPilot can automatically measure your RGB Ratio, sometimes called a G2V ratio for the spectral signature of a sun-like star.  This is a widely accepted method of determining your color combine ratios when assembling your final color image from RGB filtered data.  

To begin, first select the R; G; and B; filters.  The G: filter will be used as the reference.  Typically in English, R: will be Red, G: will be Green and B: will be Blue.  If using a BVR filter set, then R: would be R, G: would be V and B: would be B.  Then proceed as follow, depending upon your telescope control program.

To save time, CCDAutoPilot will use the binning specified for Plate Solving to initially locate the target G2V star.

TheSky6, ASCOM/TheSky6, TheSkyX, ASCOM/TheSkyX:  Point your telescope to a point in the sky near the zenith.  If Auto is checked, CCDAutoPilot will locate a number of G2V stars and slew to the first G2V star.  If you are initialized, it will center the star in your FOV.  If you don't check Auto, you will have to manually slew to a known G2V star.  CCDAutoPilot will then automatically adjust the exposure to meet its measurement criterion, take a number of flux measurements through each filter, correct the measurement for atmospheric extinction and show the resultant combine ratio.  You will be asked to inspect the first image for each star to insure there is not a close double in the image.  If there is, simply move on to another star; if not, allow the measurement to proceed.  You can measure additional stars if you wish.

ASCOM: Automatic selection of G2V stars is not possible.  Therefore manually slew the telescope to a known G2V star then hit the Measure button. 
CCDAutoPilot will automatically adjust the exposure to meet its measurement criterion, take a number of flux measurements through each filter, correct the measurement for atmospheric extinction and show the resultant combine ratio.  You will be asked to inspect the first image for each star to insure there is not a close double in the image.  If there is one, please select and slew to another star.

In general, it is advisable to measure a few G2V stars.  The expected measurement accuracy is +/- 0.1 for each star but each star's spectrum may be different.  It is also worthwhile measuring on different nights.  High, thin clouds can reduce blue transmission, leading to erroneous results. Take the median value of 5 different star measurements for best results. If you have a preferred star or stars for this measurement, do not check auto but manually slew to and center your preferred star.

At any time during the measurement, you can terminate the run via the Abort button.

A log of measurements will be displayed in the log window to the left.  When completed, you are given the opportunity to save the log to notepad.  It is also available on the Windows clipboard to paste into another application.



Focus Offset Measurement Wizard

Focus offsets were discussed earlier.  This wizard provides an easy way to determine your offsets.  Begin by pointing the telescope to a suitable focus star.  Choose one that is bright enough for your range of filters  The settings on the Focusing page will be used to run the focus routine. Verify successful manual focus on this star with your most transparent and least transparent filter in place before beginning the wizard. Adjust the settings on the Focusing page if necessary. Be sure to set the Focus Method to "Brightest Star in FOV".Note that any filters named "dark" or "shutter" will be skipped during the measurement. Obviously, such filter(s) should not be defined as the reference filter.

For most usable results, you will need to know your Critical Focus Zone (CFZ). Use the info window calculator on the Focusing page to determine the CFZ in appropriate units. Then move your focuser a known distance, noting the starting counts and ending counts. From these data, you can calculate your CFZ Threshold in counts. For example, assume you are using an F/9 system. Selecting the blue color (smallest CFZ), we see the CFZ is 58.3 microns. Assume you move your focuser 10 mm and the focuser counts change by 1000 counts over that movement. Then your CFZ in counts is 1000 X .0583 / 10 or 5.8 counts. Any change under 6 counts is immaterial. By setting the CFZ Threshold to 6 in this example, you tell the wizard to put offsets on the focusing page that exceed this threshold and enter 0 for any offsets that  do not exceed the threshold. This eliminates unnecessary focuser movements during filter changes when the offsets are not significant. If the CFZ Threshold is entered as 0, focus offsets will be reported and optionally entered on the Focusing page as measured.

Select the Reference Filter and choose the number of Measurement Cycles you want performed. A minimum of 5 measurement cycles is recommended and more are preferred.  CCDAutoPilot will set the filter and focus using that filter, repeat for each filter in the filter set and then repeat the cycle for the specified number of Measurement Cycles.  If a focus fails for whatever reason, it will keep trying until is achieved, before moving on to the next filter. After each cycle the focus offset will be calculated.  When the measurements are completed, CCDAutoPilot will calculate the median offset for each filter from your chosen reference filter and optionally enter the median offsets in the Focus Offset column of Filter Factors on the Focusing page.  The mean of the filter offsets is also calculated without consideration of the CFZ setting as a cross-check. With a sufficiently large number of measurements, the median and the mean should converge.

At any time during the measurement, you can terminate the measurement via the Abort button.

A log of measurements will be displayed in the log window to the left.  When completed, you are given the opportunity to save the log to notepad.  It is also available on the Windows clipboard to paste into another application.

The wizard will measure the difference between the minimum and maximum focus position of the reference filter. For an absoluter focuser and under good seeing conditions, this difference should be minimal, certainly below the CFZ Threshold. If it exceeds that threshold, you will know that the focuser is not repeatable and may be slipping. Some focusers home on power up, in which case, you should compare focus positions for a known star and filter manually to verify repeatability through a power cycle. If it still is not repeatable, you should not rely on any logged filter positions as representative from night to night. If the slippage is so excessive as to impact offset repeatability, you may not be able to rely of filter offset focusing strategies.



Linearity Measurement Wizard

All CCD cameras are linear over a range and then saturate or depart from linearity. Flat field frames should be exposed to as high an ADU level as possible, while staying within the linear range, to maximize the flat field frame's signal-to-noise ratio. This wizard will help determine that ADU level, which can then be used as the Target ADU for flat fields.

To measure the linear range, point our camera/OTA to a suitable constant illumination light source with no other sources of light hitting the camera. If your artifical light source is sufficiently bright, use a color or narrowband filter to have the light source overwhelm any other light sources. For accurate measurements, the light source must be constant. To verify the stability of the light source, adjust the light source brightness so that a 20 sec. auto dark exposure gives approximately 20,000 ADU. Take 10 images or so and measure the average ADU. Compute the difference between the highest value and the lowest value. The smaller the difference, the more constant the light source is. If the light source has some variation, then set the Non-Linearity Tolerance as needed to account for the light source variability. For example, assume you see a variation in the 10 images of 100 ADU. Then 100/20,000 = 0.5%. So to include this variability, you should set the Non-Linearity Tolerance to 1%. With such a light source, this is the best tolerance with which you can determine the departure from linearity, called the turnover point.

Adjust the light source brightness so that the center of the image measures 5,000 400 ADU with a 5 sec. auto-dark exposure at the desired binning. Once the source brightness is adjusted, hit the Measure button. CCDAutoPilot will take a number of auto-darked exposures in 5 sec. increments and record the exposure and ADU/sec. in the log window to the left. At the end of the measurement, a recommendation as to the maximum linear ADU will be made. It is a good idea to examine the raw data along the way as well. When the ADU/sec. decreases significantly at higher ADU, the CCD is going non-linear. If you acquire data at more than one binning, it is recommended that this measurement be repeated for other binnings used.

At any time during the measurement, you can terminate the measurement via the Abort button.

A log of measurements will be displayed in the log window to the left.  When completed, you are given the opportunity to save the log to notepad.  It is also available on the Windows clipboard to paste into another application.