Understanding latest AF update in latest SGP

Ken and Jared,

I would like to understand what you described in latest AF update in latest SGP Here is what I normally and always do when operating SGP.

  1. Slew to known star nearest target DSO, center it and sync it with mount’s hand controller.
  2. Sharply focus the star with Bahtinov mask.
  3. Use SGP’s “Slew Now” to slew mount to target DSO.
  4. Use “Center Now” to center image.
  5. Select same filter as first event.
  6. Run Auto Focus to make sure the initial focus is good and will give nice V curve. Sometimes I run AF again.
  7. Start PHD2, Select guide star. Start guiding.
  8. Click on “Run Sequence”.

Will your latest AF update affect the way I run SGP?


Indeed, I was a bit unclear on it as well.

My procedure is similar although I just focus manually and visually with a subframe, no need for a mask, then manually trigger an autofocus (not within a sequence) and make sure that is good before starting the sequence.

I would hope that when I then start a sequence, SGP would NOT revert to the absolute position (as in the focus setup) as a starting center point for focus since that would make my efforts void to a large degree.

Starting with an absolute is a nice idea as long as it only works if no other focusing has been done first, in other words. If other focusing HAS been done first, then relative should rule. Relative to whatever that preliminary focus work has come up with, of course.

This is critical since focus can change a great deal due to temperature and one should not have to be changing these “absolute” settings from season to season or day to day.

I’m commenting on this here because the other thread was not specific to this issue. I, too, would prefer to see no focuser movement other than relative offsets. I focus manually first and check framing, and the focuser will often be pretty far off from the offset locations in terms of absolute value. This would mean an extra focus run in the beginning (I’m ok with that) but more importantly the focuser could be taken far outside the usable range and possibly past the end of travel of the focuser.

What I’ve proposed in the other thread is separating focuser position vs offsets, as they are two different things. Perhaps the values in the filter setup is strictly for offsets – 0 meaning no offset, positive moves in specified steps, negative out, relative to current position. Another (single?) value would be for focuser positon, which could be an absolute position (“Go to xxxx on start”), or “Use current position on start” which would give the same behavior prior to this beta.

I think the behavior in this model would be a little more clear…

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CCDMan, the absolute focuser position thing ONLY applies if you haven’t
already done something else (like manual AF, plate solve etc). The only
time the absolute focuser position will be invoked is if you open your
sequence and just push RUN without doing anything else. I THINK that’s
correct :).

Joel –

No, it doesn’t read that way in the release notes. It looks like there will always be a movement to the absolute position, whether done manually by changing a filter, or by running the sequence…

•Prior to running a sequence, if you fiddle around and plate solve or auto focus or even just change the CFW position manually, you will find that, during your manual operations, the first change of filter wheel will set the focuser to the absolute position for the first CFW change requested (as defined in the filter table). This is OK, you are at your rig and can make sure your operations complete successfully. When you start the sequence, the first filter wheel change will cause a relative change in focuser position

That is what I would expect and hope would be the case and would make sense.
I would guess one of the SGP guys can/will confirm this.

Hmmm…you are right the release notes don’t read the way I thought they
did. Time for the experts to weigh in. :slight_smile:

I sure hope not. If you are doing something manually there is a reason you are doing it manually, probably relating to something that has changed or is different and having it go to a preset position that is ignorant of such conditions could really get in the way and cause problems.

Maybe I just do not understand the changes or am misreading or something but I had no issues with the way it was before.


I always use RGB filters and I have not yet use NB or Luminance filters so I always focus/re-focus with the filter I am currently imaging. I have not yet used focus offsets.

So, does the latest AF update refer only to focus offsets (i.e. adjust focus with Luminance and use offsets for other filters)?


My feeling is that focus should start either:

  1. At the position specified in filter setup of that filter but ONLY if the user has just started a sequence and not done any focusing prior to that.

  2. At the last focus position acquired if the user has moved the focuser either manually (by which I mean using their electric focuser that is connected to SGP) or by running (before or outside of a sequence) an SGP autofocus.

An offset to the start position would only apply if the filter being used at the start of the sequence was different than the one that was used to focus prior to or outside of the sequence (and assuming that information had been inserted into the filter setup, of course).

That’s what I am hoping the latest SGPro is doing.