The Automatic Flat action will take automatic flats at Dusk, Dawn, or using your own flat screen. CCD Commander will automatically determine the optimum exposure time to achieve your desired average ADU. In addition, CCD Commander can continuously adjust the exposure time to maintain as constant an average ADU as possible - especially useful for Dusk and Dawn flats.
Minimum Exposure Time and Maximum Exposure Time are used to bound the exposure.
Minimum Average ADU Value and Maximum Average ADU Value is range of average ADU values that indicate when the exposure time is sufficient. Once the average ADU value is within this range, CCD Commander will begin exposing your flats. CCD Commander will target half way between the minimum and maximum average value.
Number of Exposures is the quantity of flats you want for each filter.
The Exposure Setup Frame Size sets the size of the frame (centered in the middle of the detector) that CCD Commander should use when it is trying to determine the exposure time at the beginning of the flat routine. Setting this to half or quarter frame can be very useful if you have a camera with a slow download. This will speed up the exposure setup time - giving you more time (especially useful at dusk or dawn) for your actual flats.
The Flat Frame Size specifies the frame size for the actual flat field frames that will be saved.
If you don't want to save your flats, uncheck the Autosave Exposures checkbox. Be aware that you will not get any saved flats if this is not checked.
Filename Prefix is the text that is used at the start of the filename. CCD Commander will add text for each filter that is used in the action before the Filename Prefix. CCD Commander will add text for each rotation that is used after the Filename Prefix. You can change this behavior by placing the Filter and Position Angle auto-naming tokens in the filename prefix.
The "..." button at the end of the Filename Prefix text box will open up the File Name Builder window. Click the link for more information.
The Take Matching Darks function will, at the end of the Automatic Flat function, take matching dark frames for the exposures used for your flat frames. You can specify how many darks per flat to exposure via the Number of Darks per Flat parameter.
The number of matching darks could be quite large, especially when CCD Commander continuously adjusts the flat exposure time during dusk or dawn flats. Setting the Dark Exposure Time Tolerance to a number greater than 0 will reduce the total number of darks taken. This is best illustrated with an example. Assume CCD Commander exposed a set of flats using these exposure times:
3.7s, 3.9s, 4.1s, 4.3s, 5.9s, 6.5s, 7.0s, 7.6s, 8.6s, 9.7s, 10.3s, 11.9s, 13.0s, 15.7s, 19.0s
If Dark Exposure Time Tolerance is set to 1 second, then CCD Commander will expose darks that are at least 1 second apart, starting with the first exposure time. So the darks exposed would be:
3.7s, 5.9s, 7.0s, 8.6s, 9.7s, 11.9s, 13.0s, 15.7s, 19.0s
Now if the Dark Exposure Time Tolerance were set a bit higher to 10 seconds, the following would be exposed:
The Dark Exposure Time Tolerance will need to be tuned to your sensor to give you the best set of darks that can be applied to your detector.
If Park Mount is selected, CCD Commander will park the mount before executing the Automatic Flat action. This is useful if you have a flat screen that your telescope can point at when it is in the park position.
If Dusk Sky Flat is selected, CCD Commander will use its automatic dusk flat routine. No matter what it is doing when the sun sets, CCD Commander will automatically skip ahead in the action list to the Automatic Flat action and begin executing at sun set. Next, CCD Commander will slew the telescope just east of the zenith - the optimum point in the sky for dusk flats. CCD Commander then starts taking images at the Minimum Exposure Time. If the sky is too bright for the current filter, CCD Commander will continue taking exposures until the sky is dark enough to reach the Average ADU Value. CCD Commander will keep the telescope pointed at the same Altitude and Azimuth location which will cause any stars that may appear in the image to move through the frame - allowing a median combine to remove the stars from the flats. If the sky gets too dark to maintain the Maximum Exposure Time CCD Commander will stop taking flats.
You can specify where the sun should be when the Dusk Sky Flat begins. When using narrowband filters, it is sometimes useful to start flats even before the sun has fully set. The default Sun Altitude for Dusk Sky Flat is -0.83 degrees - this is the point at which the sun's disc is completely below the horizon. Set this number closer to 0 (or even positive) to start the Automatic Flat earlier in the evening. A larger negative number will start the Automatic Flat routine later in the evening.
Dawn Sky Flat acts very similar to Dusk Sky Flat. Just like with Dusk Sky Flat, Dawn Sky Flat CCD Commander will automatically stop the current executing action and skip all of the actions until the Automatic Flat action is reached when the sun reaches the specified altitude. Next, the telescope will slew to just west of the zenith - the optimum point in the sky for dawn flats. CCD Commander then starts taking images, except now if the sky is to dark for the current filter CCD Commander will continue taking exposures until the sky is bright enough to reach the Average ADU Value. Again CCD Commander will keep the telescope at the same Altitude and Azimuth. Finally if the sky gets too bright to maintain the Minimum Exposure Time CCD Commander will stop taking flats.
The Sun Altitude for the Dawn Sky Flat is exactly like that for the Dusk Sky Flat. You can adjust this value to start the flat routine earlier (larger negative numbers) or later (numbers closer to 0) in the morning.
When Dusk Sky Flat or Dawn Sky Flat is selected, the Compute Dusk/Dawn Start Time button appears. Clicking this executes CCD Commander's sun set or dawn twilight start algorithms and reports the time at which the Automatic Flat action will begin.
The Slew To option causes new fields to appear on the screen where you can specify a specific altitude and azimuth. CCD Commander will slew to the specified Altitude and Azimuth and take your flats. This is useful if you have a flat screen mounted somewhere other than your telescope park position. Just like with the others, CCD Commander will maintain the Altitude and Azimuth position during the Automatic Flat action.
Finally the Do not connect to or move mount option will do just that. CCD Commander will leave your mount alone when executing the Automatic Flat. This can be useful if you are using a flat box and have set the telescope to a specific position already.
This section defines all of the position angles you want your flats exposed at. CCD Commander will try to take all of the position angles requested for each filter, until the minimum or maximum exposure time is reached. It will move through the position angle list from the top to the bottom, taking flats for each position angle before moving to the next filter. The order of the position angles is not terribly important, although it is probably prudent to order the angels to minimize the time that the rotator must spin.
This section defines all of the filters you want to use in the Automatic Flat action. CCD Commander will take as many flats as it can (given sky condition) for each filter. It will move through the filter list from the top to the bottom, taking all the flats for each filter before moving to the next. If you are using Dusk Sky Flat or Dawn Sky Flat, the order of the filters is very important. Since the sky will be darkening during the Dusk Sky Flats, you should order your filters from narrowest to widest - this allows the narrow filters to be used when the sky is bright and the wider filters to be used when the sky is darker. For Dawn Sky Flats, you should order your filters from widest to narrowest - this allows the wider filters to be used when the sky is dark and the narrower filters to be used when the sky is brighter.
The Reverse Order button is useful when you've just setup Dusk Sky Flats and now are trying to setup Dawn Sky Flats. Rather than having to manually reverse the filter order, pushing this button will reverse it for you.
CCD Commander will automatically determine the optimum exposure time to achieve an average ADU value between the Minimum Average ADU Value and Maximum Average ADU Value before saving any exposures. During twilight flats (dusk or dawn) the sky is continuously darkening or brightening. If the exposure time is maintained over the flat set, the average ADU of the exposures will change. When the Continuously adjust exposure time to match ADU target. checkbox is checked, CCD Commander will adjust all of the exposure times to try and achieve a target ADU mid-way between the Minimum Average ADU Value and the Maximum Average ADU Value for every saved exposure. This could result in a different exposure time for every flat - so be sure to normalize the flats when combining.
The Use Global Image Save Location checkbox enables you to specify a different path for your flat images. When this is uncheked, the "..." button is enabled and you can select a different location to save these images.