Autofocus verification exposure

Hello. It would be nice if SGP took one test exposure after the auto exposure run to verify that the auto focus was succesful. It would also be great if the user could define some HFR limit for acceptable focus. If stars in the verification exposure are larger than the HFR limit after auto focus, the auto focus could be run again.

That seems reasonable as a user option. I don’t think it would be good to always do it, rather have the feature user selectable.

Something else that is related that I have always wanted to see is what I would call “smart filters”. As everyone knows, when doing LRGB (or any image where one channel is being used as luminance), the luminance images are the most seeing critical, whereas the RGB (or whatever other filters provide just color data) are less critical.

In fact, I can’t speak for others but it is quite common for me to do only L or only RGB on a given night or part of a night based on the FWHM of the current image(s) and (in my case since I have one) what my seeing monitor is telling me. You can also usually tell from the quality of the tracking, which is directly related to the seeing - at least for a good mount.

It seems to me that one could use that focus verification image as a way to keep track of quality and have the ability to switch from seeing critical filters to seeing non-critical filters (or the other way around) based on what the HFD is on those verification images. Post focus verification images might be a somewhat better measure for such a feature than the actual images since focus drift would not be a factor.

Is the problem for which this is the solution that an autofocus routine that is reliable is needed?

Checking and doing multiple autofocus runs won’t help if it isn’t working.

Well, the autofocus has seemed to be fairly reliable, but I would still like some sort of a confirmation of the final result, instead of waiting for the next 10-20 minute exposure to finish before seeing whether or not the focus is spot on. Eventhough the routine is fairly reliable, it can still fail due to e.g. a gust of wind shaking the telescope a bit during the focus run or whatnot. In that sort of cases rerunning the autofocus routine helps. The autofocus window even has a button for running the focus routine again. The confirmation exposure doesn’t take long, so it doesn’t do much harm either.


I think this is a good idea , a user selectable option should not be too hard


The trouble is that it doubles the complexity of SGP. Is that worth it just because it would be nice?


IMO a tick box tucked away somewhere would not double the complexity , but we will see what the “all seeing eye says”


I don’t really understand how that would “double the complexity of SGP”. It’s simply a matter of checking the HFR after autofocus and possibly running autofocus again.

I don’t see that either. Perhaps he meant my “smart filter” offshoot idea. That would be certainly be somewhat more complex than a simple check.

But I am not a coder of any consequence so I will leave that question for the authors.

The number of ways that SGP can be set up would be doubled because everything could be done with or without this feature.

Users (or marketing) will often specify a solution when in reality there is an underlying problem or something that they want to achieve. I have found that if the actual underlying problem can be defined there is a better and simpler solution. Simpler can be for the developer as well as the user. It requires thought and discussion to do this though.

This looks like one of those solutions. What does acquiring another image and doing a check on the focus do? By itself nothing other than satisfy the curiosity of the user. In reallity it would also need some sort of threshold and decision to do something. This is where the complexity really mounts up. How do you test that? How do you handle the errors? It will generate a vast amount of calls for support, further refinements and so on.

So what is the user trying to achieve? In focus images I suspect. For that an auto focus method that works reliably would be a better solution than a sticking plaster over one that’s not reliable. Simpler for the user. Simpler for the developer because the overall structure of the application isn’t changed. All the change is in one place where it will be more amenable to development and, crucially, testing.

I’m trying to avoid SGP becoming a bloated, unusable and unreliable monster. Every additional feature is a step on the way to that. It’s very easy for the experienced users not to see this because everything else is familiar but a new user will be overwhelmed.


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I have to agree. When thought patterns are already slowed by lack of sleep is a poor time to make decisions. A highly complex software with lots of options is a recipe for frustration and a wasted evening. I’m all for keeping the user interface as simple as possible to benefit the most people. Maybe an added-cost module would be better?

Firstly, the SGP method is at least as reliable as the competition, perhaps more so, and I have a lot of experience with both. OTOH no method is (or can be) perfect. 20 years of imaging have taught me that there are three things that most commonly cause image failures:

  1. User error
  2. Cheap equipment - which is also “user error” :wink:
  3. Sky conditions

Software should not have to deal with the first two (although it can help a bit sometimes) and can have trouble dealing with the third due to it’s random nature. That is why beyond some point even the most perfect software solution needs to go to the user and say “this is not working” and ask for input. In this case that means giving the user the ability to check the focus and let them know if it is outside a user defined range.

I would agree that I am not in favor of just redoing the focus indefinitely. That reminds me of the classic “definition of stupidity” - trying the same thing again and again hoping for a different result.

I would note that FocusMax has always had this feature and it’s solution is to just return to the previous focus point - less than ideal, IMHO, since one focuses for a reason. I would personally just prefer that it let me know so I could take action.

Bottom line - I would like to see it check focus and let me know if it was beyond a certain HFD. This should be optional and not enabled by default.

As far as my “smart filter” idea, it would be great but I do realize it would add quite a lot of complexity. I threw it out there mainly as food for thought since suggestions are how new features get started.