I really appreciate that Gene put in so much work to help identify the problem. I have worked with Gene over the years both with his guide interface and his focuser and really appreciate his can-do approach.
I also want to thank Mark for resurrecting this issue when others of us had just plain given up - largely out of exhaustion. And thanks to the SGP developers for giving it another look.
I’m glad this bug was finally found, but I think an important thing to note is that this problem has been reported numerous times - and in each thread there are other people saying they have the same problem and want some kind of delay.
Here is my post from July '16:
So I think many more people were impacted - including those with Crayford focusers who wouldn’t even have noticed focus was changing during exposure. Now that the bug has been identified it should be more clear how many people were affected. I’m just not sure about other people who had this problem and didn’t have a different camera to switch to. Did they just give up on autofocus and sgp?
There were many assumptions going on - but a key point in all of it is - SGP autofocus just doesn’t work at all with my current setup. Can it be fixed?
My assumption was that a delay was needed and the exposure is happening too soon after the movement. At the same time - the counter assumption was - my setup is weird and has problems - and adding a delay is not justified since things seem fine for most people.
When a user has a fundamental problem that kills overall functionality - it is quite irksome to be told that efforts to fix it should not be attempted since it would violate some “pure” concept of the software design. Especially when things like delays are all over the software - and it isn’t pure in the first place.
At the core - I was a user with a setup and a camera - and autofocus just did not work at all - because every focus image was streaked. If you can’t autofocus with your setup - most of sgp’s features are useless because otherwise you need to focus manually during the imaging session.
Meanwhile - I was able to use other cameras and it all worked fine - so I did have a fallback. But since it worked just fine with other cameras - it was evidence my equipment was working fine and something else was causing a problem with the other cameras during focus. There was a bug in there - and it was insidious - but certain setups showed the problem consistently.
If anyone has had ugly focus curves and erratic autofocus behavior - this fix may help - and they should look at their autofocus images to make sure the stars aren’t streaked.
And even if their curves have looked good so far - they have a chance to improve now if focus was changing during exposure and they didn’t even know it.
Frank