Process to avoid focuser associating previous ending position with next nights starting position

I have a small challenge to face with SGP - it is a Moonlight focuser / process issue really - so I need a best approach solve rather than any coding I reckon!

So the issue is each night the Moonlite focuser associates the starting focus position at the end of night temperature with whatever position the focuser ended the night before (on a far lower temperature)!

So I get the focus maybe moves in 200 steps from start of night position with a temperature in the low 20s to and end of night position with the temperate around 10 celcius - but I would expect to see on the following night the pattern repeat as the same offset - but it looks more like the Moonlight focuser when it disconnected associated it position with the current temperature - rather than the position where it ended the night.

So log viewer shows the same shaped curve - but starting at a lower base point each night!

So its a relative issue. If I turn off the focuser at 10 degrees at position say 5,200 - and then the next night I turn on the focuser at 20 degrees and its still at position 5,200 - then it associates that 5,200 number with the 20 degree temperature - not the ten degree temperature of the night before.

So I can see a few possible process work arounds:

  1. never turn the focuser off - and leave it auto temperature compensating in either the driver or the SGP software running the focuser with temperature compensation enabled - probably work a treat but not ideal

  2. at the end of the night always go back the the starting position of the first night - say 5,500 for 22 degrees celcius.

  3. at the start of the night - before connecting the focuser to SGP - use the hand controller to rack it in to position zero. Then connect SGP and tell SGP to move the focuser to position 5,500.

  4. At the start of the night simply tell the driver to reset the focuser position to 5,500.

  5. Request SGP record the end of night focus temperature - and upon connection suggest - hey you are 10 degrees and 200 steps below where you started teh night before - want me to move the focuser back to where you started the night before at X temperature?

Wonder if there is any sixth option? Which option would folk advise - I am think 1 would be interesting - but 3 is probably safest!

The linear fit line - similar slope but starting point is associated to the wrong temperature / postion - causing inward creep!

and on the second night

I think for now I will have a process where I capture the start and end of night positions - e.g. tonight started at 5,272 and ended at 5,139 - so assuming tomorrow will be roughtly the same temperature at the same time I moved the focuser back to 5,272 then diconnected it - then started the camera warm up process.

This way at least the camera will start at the same location - if not at the same temperature.

I am still convinced that te best process is likely to move the camera all the way in and set that position to 0 at end of night then on start the next day move the focuser out from zero to wherever you started focus the last day and then run a focus.

Will think on this some more!

FYI - SGP night three - after racking the focuser back to the previous nights starting position.

Think I will have to go with move it all the way in with focuser no connected in SGP - then move to out to around 5,500 at the start of each night!

Three consecutive nights - three parallel lines - different starting positions implying the focuser starting position is not true!

A beta (1139) has been released to help deal with this. It obviously will not work until the second night it is used. Of course, if your focuser is unbale to return to the same mechanical position using the controller, then it also won’t work. Logging around it pretty verbose at the moment so should be easy enough to track if it’s not working as you expect.

“• At sequence start SGPro will conditionally return the focuser to the position of the last known start (but only if the time of day of the current start is within plus / minus 1.5 hrs and the calendar day is plus / minus 15 days). This only applies to the ‘Focus before Sequence Start’ trigger.”

What about…

This is what I use. Works great for weeks until perhaps the temp differential calls for me to change the figure in the filter list.

Or…if both are active…which will take precedence?

I am in the process of “pre-documenting” the new feature in another post, but just for clarity, that feature no longer exists in the beta. It has been superseded and promoted to the main control panel focus tab here:


That’s not to say that we can’t have both options in the final release, but the intent is that the new option completely obsoletes the old (also if the new positioning system fails to determine an appropriate position, it will default to the old behavior and just move to the absolute position anyhow).

OK Ken…thanks …we will see how it pans out but looks like you have it covered :slight_smile:

Here is the page we can use to discuss…

New SGPro 4.3 Feature: Automatic Focuser Positioning at Sequence Start - Sequence Generator - Main Sequence Software (

Hi guys

It’s great to see continual progress - I will try it out by the weekend!