Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Usage questions ..
(2018-09-25, 05:09 PM)theskyhound Wrote: Hi,

Thank you for explaining your workflow in detail. It helps me better understand what needs to be done. I am working on a feature to avoid meridian flips, but I haven't quite yet figured out how it should work. If you don't mind, I'l like to ask some questions.

1. When you spoke about two different "target lists" and scheduling them, that didn't make sense to me. Did you really mean two different Observing Programs? I ask this because you can't really schedule from a target list, but people are clever, so you never know. ;-)

On the main dialog there are several tabs, "Target Selection", "Scheduler", "Real Time Imaging" and "ACP Expert" ... on the "Target Selection" tab there is a combo where you can pick a grouping of targets to choose from; NGC, Messier, Skyhound, RASC Best, etc. which simply groupings of DSO's.  On the target selection dialog a user also has the ability to create their own "target lists" which is what I've done ... so, on the "Target Selection" tab when I select the "target list" to view I select one from SiteA, SiteB, etc. based on the seeing criteria (see below)

2. You spoke of "fine" detail, as if it is a setting somewhere in SkyTools. Someone else (or maybe you) mentioned the same thing on another thread. What do you mean by "fine" detail?

In the "Image Project" dialog, there are several tabs, "Basic Properties", "Composition and Tiles", "Exposure Goals and Filters" and "Observations" ... on the "Exposure and Goals" tab there is an "Expose For" group box, inside of which you can choose the level of detail for the object; for a galaxy that would be "Nucleus", "Main extent/ arms", "Halo", "Faint Halo" which correspond to a level of detail; "Nucleus" would be very coarse, "Main extent/arm" is better (but the nucleus might be blown out), "Halo" is finer (but the nucleus is definitely blown out and the arms are likely getting bad) and "Faint Halo" is highest level but everything else is blown out ... nebulae have a similar grouping of "level of detail", I simply use the "fine" with for galaxies would correspond to "Main extent/ arms"

3. Your approach to scheduling primarily via SQM readings is quite unusual. Am I reading right that your sky brightness varies from 21.2 to 21.3 (more or less). If so, that puts your location at a fairly dark site. I understand that noise from the sky may dominate anyways, but sky noise is a big part of the SNR model that SkyTools uses. So I am not sure that it is justified to put sky brightness, particularly over such a small range, as the top consideration. I'd be interested in hearing more. Are you directly concerned about sky brightness itself, or are you using it for a proxy for something else, such as transparency?

You're correct both that I'm able to image from a dark site where I have my scope "farm" running semi-remotely as well as the SQM varying by around .15 based on the time of year, mainly influenced by high clouds brought in by the monsoon season in early summer there.  I agree that sky noise is taken into account by ST4, but remember there's a bigger ecosystem here than just exposure calculations of lights ... namely, remember that I need to be able to stack these together at some point, and stacking has it's own rules ...

Recall the way that stacking programs work: very simplistically given a set of lights, they essentially do an averaging of each registered pixel across all of the supplied lights, adding pixels as needed and removing them as needed but with the assumption of a certain degree of uniformity between the lights.  One of the big things to watch out for with stacking is to not "poison" the stack by giving it an outlier light that might throw off it's algorithms, which is why we need to preprocess the individual light prior to stacking for dust motes (flats), hot pixels (dithering) and dark current wells (darks) as well as amp glow/ well irregularities (bias).  We might also try to do SOME background mitigation using PixInsight PixelMath and DBE manipulations at this point (I'm reluctant to remove raw data since I can never put that back), but the idea is that each individual light has as much non-uniform data removed from it as possible prior to doing the full stack.  Note that these manipulations have absolutely nothing to do with exposure time calculation ... these are to keep the stacking app happy ...

As part of this "quest for uniformity" we need to make the sky noise as uniform as possible; that's why we don't mix lights taken from an SQM 21 site with lights taken at an SQM 16 site in our stack ... although PixInsight can flatten noise pretty well with DBE and PixelMath, it's easier just not to have that skyfog noise variation there in the first place.  With this knowledge, and with the desire to keep this sky noise as constant as possible between lights and with the ability to get an idea (with my SQM meter) of what the SQM is each evening I simply use that to do a sorting of the lights by SQM gradation ...

And you're correct, this has nothing to do with transparency (which is seeing), and I can get that from the FWHM of the guide star for that evening; that brings in a whole new universe of target list sorting I do:

- If the calculated seeing is .8 or less, then I image all of my fine detail objects (small galaxies, planetary nebulae), those are placed in target list "Site A Fine"
- If the calculated seeing is .8 to 1.5, then I image all of my coarse detail objects (reflection nebulae, larger galaxies), those are placed in target list "Site A Coarse"
- If the calculated seeing is 1.5 to 2.0, then I image all of my binned stuff (generally larger nebulae and larger galaxies), those are placed in target list "Site A Binned"
- If the calculated seeing is 2.0 or larger (rare, but it happens) then I run my HyperStar objects, generally really big nebula like Veil, those are placed in target list "Site A HyperStar"

4. Regarding meridian flips. I think I understand but I want to ask to be sure. Is your goal that all images be taken on the same side of the pier for a given project? Or is it such a pain to do a meridian flip because of refocusing or whatever, that you want to do as few as possible on a given night?

For a given night I don't want to do ANY meridian flips for that evening ... the issue is that for larger SCT's like my C14's and C11's mirror flop is a significant issue when the scope transits the zenith and the mirror/ focuser tube "flop" from one side of the baffle tube to the other ... other than causing an image shift (which platesolving can fix) that will throw off the collimation of the OTA to some extent and now I've got fuzzy lights ... there are lot's of threads about this on CN and lot's of fixes, but each "fix" has it's own issues and problems that they introduce.  The best solution that I've found is to "just say no" to mirror flop in the first place by not letting the OTA transit the meridian.  When I collimate the OTA it's orientated E or W and is so marked, and I'm careful not to let the OTA "flop" from that orientation during transport or storage so that my collimation won't change.

Refocusing is easy (I use FocusMax and/or SGP), and I refocus before each light anyway to compensate for thermal changes ... it's the mirror flop and the loss of fine collimation I'm avoiding ...

5. I have the beginnings of an idea in mind to schedule in such a way as to limit the number of meridian flips. It works on the assumption that your goal is to minimize the number of flips during the night. So based on that assumption, how many times do you normally flip during the night? How do you decide when to do the flip?

The goal is "no flips period", and by creating two locations, each with an obstructed horizon, it's easy to do that ... location "E" has the horizon obstructed from 175deg to 360, location "W" has the horizon obstructed from 0 to 185deg, done and done.  I have "locations" stored for each site A based on pier side and SQM; A E SQM 21, A W SQM 21, A E SQM 20.8, A W SQM 20.8 and so on down to the last SQM.  Each "location" is set with the appropriate obstructed horizon and SQM level.


So, in summary here's what I've got so far for my workflow that I'm experimenting with using ST4:

- Once I've determined the seeing for the site I'll load in the appropriate target list in the "Target Selection" tab, say that I think it's going to be a murky 1.5 seeing day so I load in the "Site A Coarse" target list 
- I take the last night SQM reading, say it's 20.5, so I load in the location "Site A SQM 20.5 E", set my imaging and telescope system as appropriate (I have C14's and C11's) and generate my schedule for the E pier scopes
- I then load in the location "Site A SQM 20.5 W" and generate my schedule for the W pier scopes
- The SGP's controlling the E scopes get the E schedule, the SGP's controlling the W scopes get the W schedule ...

SGP on each scope does it's thing, hopefully properly ...

- During the day I take my flats for each scope
- I combine the flats for that scope, the lights it took that evening, a master dark for the temperature and that scope sensor into a zip file labeled for that date/ SQM/ scope/ FOV and file it away
- Rinse, lather, repeat day after day, week after week, month after month ...

Eventually I have enough light zips accumulated for an object (generally 50+) by scope type, SQM, and FOV that I unpack everything and stack it all up with various stacking apps, if I like what I see then the result goes into PixInsight/ APP/ whatever ...

Hope this gives a bit more clarity! Smile

Messages In This Thread
Usage questions .. - by choward94002 - 2018-09-21, 12:25 AM
RE: Usage questions .. - by theskyhound - 2018-09-21, 03:27 AM
RE: Usage questions .. - by choward94002 - 2018-09-21, 12:58 PM
RE: Usage questions .. - by theskyhound - 2018-09-21, 02:50 PM
RE: Usage questions .. - by choward94002 - 2018-09-21, 03:36 PM
RE: Usage questions .. - by theskyhound - 2018-09-24, 04:24 PM
RE: Usage questions .. - by choward94002 - 2018-09-25, 02:34 AM
RE: Usage questions .. - by theskyhound - 2018-09-25, 05:09 PM
RE: Usage questions .. - by choward94002 - 2018-09-26, 04:03 PM
RE: Usage questions .. - by theskyhound - 2018-09-26, 08:39 PM
RE: Usage questions .. - by choward94002 - 2018-09-27, 12:04 AM
RE: Usage questions .. - by theskyhound - 2018-09-27, 05:14 PM
RE: Usage questions .. - by choward94002 - 2018-09-27, 08:35 PM
RE: Usage questions .. - by choward94002 - 2018-09-27, 11:20 PM
RE: Usage questions .. - by theskyhound - 2018-09-28, 03:48 AM

Forum Jump:

Users browsing this thread: 1 Guest(s)