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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Image HFR History

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Replied by Rob Lancaster on topic Image HFR History

Right, I forgot to make that part clear. It takes a separate focus image or subframe between each light image now. I agree that it would be nice to just use the light image for the hfr history and monitoring. But one issue I can see immediately is that a longer exposure will make the star appear bigger so using that for monitoring hfr and comparing it to a specific value that was derived from an autofocus image could prove difficult. Not to mention that the light images could be taken using different filters and the star could appear bigger or smaller in different filters due to the color of the star or chromatic aberration of the telescope or filter
4 years 2 months ago #47379

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Replied by Andrew on topic Image HFR History

I don't think it has to match the HFR of a focus frame, since long exposure light frames that are comparable with each other.
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4 years 2 months ago #47381

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Replied by Alfred on topic Image HFR History


Thank you very much for the clarification. That's right, light frame HFR values cannot be compared to focus module HFR values. I would prefer comparing light frame HFR values only and leaving the focusing module out of the equation (for the purpose of tracking light frame quality) completely. Of course seeing will increase stars for long exposures but sub-optimal focus will ADD to it so I would expect derived HFR values to be fully meaningful still. With regard to filters HFR values should be compared among their respective groups only.
Last edit: 4 years 2 months ago by Alfred.
4 years 2 months ago #47382

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Replied by Alfred on topic Image HFR History


Let me clarify: I meant the user should take track of what filters have been used. I didn't ask for Ekos to keep track of it. I'd like to keep it simple and add more functionality later as needed/time allows.
4 years 2 months ago #47385

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Replied by Rob Lancaster on topic Image HFR History

So the reason I mentioned comparing hfr values with focus frames vs light frames is because the current functionality uses a focus frame between each light frame to keep track of the hfr to determine if an autofocus is necessary. The simplest implementation of the idea that was proposed would be to just take what is already there and just log the results on a graph. But if we want to change that to make it use the light frames instead to keep track of the hfr we would need to think about this so that we don’t break the autofocus monitoring that works right now.
4 years 2 months ago #47407

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Replied by Andrew on topic Image HFR History

I was not aware the autofocus monitoring worked that way. I suppose I can understand why, but it must take a fair amount of idle time to capture and download additional frames.
We must also consider the graph will be used by those who do not have motorized focusers to tell them when to manually focus. How does the current HFR monitoring system work if no focus driver is running?
However, I do see an advantage of taking separate focus frames that will be less likely to have any star trail issues of guiding is not used or was poor polluting the measurements.
4 years 2 months ago #47408

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Replied by Rob Lancaster on topic Image HFR History

I am not sure because I only found how the current hfr monitoring function works when I started looking into adding the hfr monitoring graph that started this thread. I knew that the checkbox was there, but I don’t tend to use that feature because I typically just start the autofocus myself when I feel it is needed. So I didn’t realize that it mostly did what we were looking for already, except that what I would like personally is a graph with a report as to how the hfr has progressed over time and I do not want it to autofocus itself automatically when the hfr gets to a certain value like the checkbox says currently. I still want to decide myself when to autofocus.
4 years 2 months ago #47414

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Replied by Alfred on topic Image HFR History

So we agree on almost everything. A HFR value derived from a light frame would do more than just check the focus. It would provide a comprehensive measurement of image quality and make users aware of problems other than just a deteriorating focus (like guiding issues for instance). The important thing IMO is to become aware of such problems as soon as possible (certainly before doing image processing the day after as it happens now) in order to avoid taking useless light frames and wasting precious observing time. The focus module could be left totally unchanged and do re-focusing as it does now. In addition to it, the "global" HFR value would be calculated and displayed (with or without graph) whenever a light frame is received. It would be 100% up to the user to perform re-focusing, check guiding, or take other measures in order to improve image quality then.
Last edit: 4 years 2 months ago by Alfred.
4 years 2 months ago #47427

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Replied by Peter Sütterlin on topic Image HFR History

Yes, this is what I currently do. I run an external program that watches for new files, analyzes some (preselected) stars by fitting a 2D moffat model and then plots FWHM and ellipticity. (It also aligns images and gives a live stack view). Ellipticity usually points at guiding errors and/or wind, FWHM obvious focus errors, but also seeing quality. I do get a very good correlation between the FWHM variations and seeing measurements using a DIMM (Differential Image Motion Monitor).

The latter is one reason I don't use the automatic monitoring by EKOS anymore. There is no real way to decide if the focus drifts or the seeing gets worse, unless you also include the temperature plot (unless of course your focus system has slip). So a general monitoring module definitely should also include the temperature (but I think that is already on the wishlist, is it?).

As for monitoring in EKOS: How much work would it be to grab the (full field) star selection and HFR fitting from the focus module, and put it into the FITS viewer? I know it even already has a 'HFR' slot in the statistics which is always -1. So it seems the evaluation part is (still) missing...
4 years 2 months ago #47429

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Replied by Alfred on topic Image HFR History

Is this external program open source so its functionality could be implemented in Ekos easily?
4 years 2 months ago #47438

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Replied by Peter Sütterlin on topic Image HFR History

In principle it's not secret (though not published anywhere). But I do all my image processing stuff in IDL (Interactice Data Language), so as-is it's not really helpful to others. Last time I tried GDL wasn't able to run all needed stuff in there. It's anyhow only an ugly hack (comparable to some shell script) that likely only works for my camera, screen and data organization :(
As always, the difficult part is not the core math (Levenberg-Marquardt fit), but the effort to make it work on any image, and nicely display the results.
4 years 2 months ago #47442

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Replied by Alfred on topic Image HFR History

I recently found that han.k's ASTAP offers HFD functionality.



Currently I use astap to check the quality of my images during a session. As soon as the latest light frames show deteriorating HFD values, a re-focus is initiated. I think it would be handy if FITSViewer could show the HFD value of the picture it currently displays, too. Also, the summary screen should display the same number. I don't know if han.k's code is in the public domain but if so, it shouldn't be too complicated to implement it in Fitsviewer and the summary screen.
Last edit: 4 years 2 days ago by Alfred.
4 years 2 days ago #51226
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