Below, please find the description of a new capability which utilizes a combination of Priority and Hour Angle controls to acquire frames in a way that will tend to maximize resolution and minimize extinction.


The software is ready to upload but before releasing it I would like to solicit comment on this from the ACP Expert users here who use CCDNavigator. This scheme provides approximately 6 hours of imaging each evening and limits each filter to an hour angle range. The easiest way to understand this is that each filter is limited to a range and given a priority so the data from more critical filters are acquired at higher elevations.


Some of you may want it to run for a longer period of time each night however this can lead to acquiring data at unacceptably low elevations. Nevertheless, I am open to changes in this regard so let me know what change you'd like so we can discuss it.


I am confident someone will ask for all the parameters in the table to be made customizable by the user. I will resist this since it would be easy to get the values into a state where totally crazy things would occur. So propose whatever changes you might like to see and give me your reasoning for them.


Once this version is released, most of you will need to purchase a License Renewal so the new feature will be enabled.


Steve Walters


Author - CCDNavigator


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ACP Expert Hour Angle Limits


Beginning with CCDNavigator 3.1.14, a new capability has been added for ACP Expert users. When a Request is being generated for a target, the CCDNav3 “Goals” screen has a new checkbox titled “Use Hour Angle Limits”. If this is checked (you can establish a default for this in the “Camera” menu), a combination of ACP Expert Priority and Hour Angle Range is used to schedule 30 minute long blocks of frames. These will cause ACP Expert to expose the filters when the following Hour Angle Range and Priorities are met:



“Base” is equal to 10 times the Priority set in the “Goals” window of CCDNav3. With this arrangement, every filter of every target will have a unique priority. In this way, the user can schedule multiple targets with different priorities which will not interfere with each other. For instance, if the user sets the CCDNav3 “Goals” Priority to 3, then the base priority is 30 so the Green filter would have priority 37 and a Clear filter would have priority 40. If the “Goals” Priority is set to 4 (for a different target), then the base priority is 40 so the Green filter will have priority 47. Remember that ACP Expert will image the frames with the highest priority that are within the two Hour Angle limits.


Notice that theNarrowband (NB) filters have been assigned the same Hour Angle Limits as the wide band filters but with the lowest priority. This will cause ACP Expert to acquire NB frames after all of the LRGB frames have been completed so time is available within the specified Hour Angle limits for low priority.


This arrangement works best when the target to be imaged transits in the middle of the night. This situation is referred to as “Opposition” and CCDNavigator's “Information” window will tell you the date when this occurs. On the Opposition date, there are equal amounts of imaging time available on both sides of the transit so this allocation of hour angles will work very well. Assuming that ACP Expert has no other targets to image, it will first take Red frames for 1 hour, then Green frames for 1 hour, then Blue frames for 1 hour then Luminance frames for 3 hours, followed by an additional hour of Blue frames, an additional hour of Green frames and finally an additional hour of Red frames. This can be described as RGBLBGR.


This method will tend to minimize the effects of seeing because the most important frames for high resolution are the Luminance data and they are taken at the highest elevation. Further more, by scheduling the R, G and B frames as described, the effects of atmospheric extinction are also minimized by taking Blue frame at the next highest elevation, Green at the next highest and finally Red and the lowest elevation. This scheduling method will, in general, produce the highest resolution images with the least color extinction possible.


Before you decide this is sheer perfection, you should recognize that there is a slight downside. Suppose that ACP Expert images a target two weeks after the date of Opposition. By then, the target will transit roughly 1 hour earlier. This means that the Red frames which would have been taken during the first hour will be skipped and Expert will move directly to taking Green frames. And the Red frames that would have been taken at the end of the session will be beyond the West Hour Angle Limit and will also not be taken. All is not lost however, eventually ACP Expert will have collected all the other frames and the Red frames will be acquired during one of the intervals. And in any case, all of the data will be acquired at hour angles that tend to minimize the effects of seeing and extinction.


So, it is best to create requests that use this method a week or so before the Opposition date so the target will generally be well positioned for using this method.


Also, note that there are many unscheduled activities that will take place (such as slewing, plate solving, focusing, etc.) which can cause ACP Expert to not commence acquisition of frames precisely on these 30 minute schedules. Therefore, the actual amount time spent on any given filter during the session will vary as it is not possible to predict these interruptions.