Temperature Compensation Fix


It appears that SGP temperature compensation only considers the relative temperature change between the last 2 frames, and not the absolute temperature change from the start of the run. This means that it ignores any step change of 0.5 or less for each sub. This becomes an issue when there are repeated small temperature changes which result in the required step change each time to be between 0 and 0.5, in which case the movement gets rounded to zero. Last night I had a run where there were 25 consecutive subs of small temperature changes - the focuser wasn’t moved at all, but should have been moved by 7 steps total. This is a pretty significant error for anyone with scopes which do not change much with temperature, but which are focus sensitive.

Temperature Compensation Implementation
OPTEC Temp Comp focuser
When will this bug be fixed eventually?

The issue with SGP applying wrong focus corrections due to temperature change is indeed a severe one. See:

for a correct Temperature compensation algorithm.




Has this feature request been implemented so far?
If not, then i will give this a +1 as well!
(also an FSQ-85 user here, where this seems to be highly important)


Well, you are generous calling this a “feature request”. It is really a request to correct an error in the program, which to my knowledge still has not been addressed or even acknowledged. I am not sure why, since it does not seem like it would be a difficult fix.

It is an error which impacts everyone who uses the temperature compensation, but it only significantly affects those of us with telescopes which are well designed to be temperature-stable. My other cheaper Orion scope is not temperature stable, so the algorithm error does not have as much impact.

Despite this issue, I recently upgraded to SGP 3.0 because I love the rest of the program so much. Skies have been cloudy since then, so I don’t know if the upgraded version has incorporated a fix to the error.


Gary, you are right, temperature compensation is not working correct in SGP - and this is not a missing feature but a bug. With this bug unfixed it is not at all advisable to use temperature compensation, which is a feature that was advertised already for v2 of SGP.

Yes, it’s time for fixing this. The correct algorithm was given here: Temperature Compensation Implementation

@Jared: And, please, consider my related requests (post:8, topic:6781):