Autofocus failure

[Joe Morris]

The autofocus routine failed several times last night because of low flux readings. I'm using ACP 6 hotfix 4 and FM 3.6.0.77. The "Use FocusMax Acquire Star feature" is unchecked. Attached is one of the autofocus log files. Also is attached the p-AutoFocus image which shows a fairly bright star, well centered, that I assume was used for the autofocus routine.

Probably should have checked the "Use FocusMax Acquire Star Feature" just to see what would happen but didn't think of it. If I manually ask FM to "focus" while a fairly bright star is in the image field, the focus routine runs fine.

I was also surprised that ACP gave up after only one try to autofocus.

Joe Morris

[Dick Berg]

Hi Joe,

At the point in the script where it failed, FocusMax is controlling the operation, not ACP. FocusMax gave up - because you have the maximum exposure set to 5 seconds and the required exposure was predicted to be way more than that. The real question is why was a 72. mag star was apparently so dim (only 4000 adu). I would try again, a couple times in different parts of the sky, to see whether there is a consistent failure. Could just have been a one-off event. I don't think using the Acquire Star Feature will change things. Good luck.

I don't know if your operating remotely, but FocusMax does show the position of the focus star on the imaging chip (upper left-hand box, I think). You wouldn't see that if you're remoting in.

[Joe Morris]

Thanks for the information, Dick. I was sitting right in the observatory when this happened and I believe I could see the focus star in the smaller box but that's only my memory. There were passing clouds that night but it happened several times after I saw a pretty nice autofocus pointing exposure made. I do need to use the USNO catalog because of the 2000mm FL telescope but that probably has nothing to do with the problem.

Joe

[Jim McMillan]

Joe,

Do you have the FocusMax log? Only if we have that can we be sure what happened.

BTW, ACP doesn't "give up" focusing. It just reports that FocusMax wasn't successful after one try (and one try only). So, why wasn't FM successful? My guess is that there was another star "too close" to the one ACP picked to focus on. Occasionally, ACP will pick a star to focus on that, according to the catalogue database, isn't a double. But, in fact, it is. FM usually can't successfully reach focus when this happens. A year or so ago, ACP added functionality to exclude these "bad" stars in the file BadBrightStars.txt. See ACP's help file to see how it works. This is the contents of my file.

 2:10:54     39 02 36
12:28:05    44 47 36
22:36:08    35 34 38

The first target where this is a problem is NGC 891; the second is M 106; the third...I forget (GSC).

AcquireStar will pick 3 stars to try to focus on. If it fails on the first, it tries the second, and so on. In that sense, it's a more robust process. However, it also takes a little longer, so there's a trade-off.

FWIW.

Jim

[Joe Morris]

Thank you, Jim for the reply. I did start a personal BadbrightStars.txt but only have one additional star added to the ones you mentioned. I'll switch between using ACP and FM AcquireStar routines and see if one works better for my setup.

I looked for the FM log without any luck but will look again when I'm at the computer that was running the observatory. I looked in the "Log" tab of FM and it only had very recent history. Are the old logs files in a hidden spot?

Joe

[Jim McMillan]

Joe, there's an option in FM for it to automatically put the FM log into ACP's log. I find that's the most convenient way to monitor what's going on. You'll find that option in FM under Open, Options, then check "send log txt to ACP".

Jim

[Lloyd Smith]

Is there an option to have ACP request additional autofocus executions in the event Focusmax fails, or is Acquirestar the only way to get this behavior? Thanks.

-Lloyd

[Bob Denny]

LLoyd, I am unsure what you mean. Do you want ACP to keep calling for an autofocus if it fails? How many times? Is there an underlying problem that you're thinking this would "solve"?

[Lloyd Smith]

Yes, I would like for there to be more than one try--some reasonable number of tries, or even user a assignable parameter. There are various normal situations that could cause focus to fail (a passing cloud for example). I would like the result to be at least another try. The current recourse is to have Focusmax return to its prior position (which we know is out of focus), or presumably, to stay at the position it was in when focus failed (I only use the return option in Focusmax). Ideally focus would never fail, but that's not the case.

[Bob Denny]

OK, I'll look at it but there are consequences to this. Scheduler needs to guess how long a focus takes. So does Planner. If it spends too much time trying to focus because it doesn't meet the HFD requirement on a night of poor seeing the target timing can be altered significantly. Remember that not everyone takes long (>5 minute) images...

Again, why is the focus failing? Is this usually the first focus of the night? Are there others here who can chime in? Why would this come up after 10 years? I don't see much trouble with FocusMax at the several observatories I use for engineering.