Minor feature request for when you run out of other ideas

Like that’s ever going to happen. :grin:

One of my minor frustrations is that I typically need to manually tweak focus at the start of a sequence to get it close enough for AF to take over. This is due to the often large temperature swing between when I finished imaging the previous night and when I start the next sequence. In fact, this is the only thing that prevents me from letting a sequence start unattended. Starting focus is never good enough for AF to work well, and smartfocus runs amok as often as it works well.

It would be cool if SGP could start the session with the focuser set to a temperature compensated starting point. You already have almost all of the pieces of the puzzle in place to set the focuser to a very good temperature compensated starting focus point.You have the temperature coefficient (for those who use it). The only other thing you need is an intercept - which can easily be determined from the temperature and position in a well-focused image.

It could work like this - Let’s say that the temp coefficient is 20 steps/degree. From a well focused image we establish that the focuser was at position 1000 and at 20 degrees. From that, we can calculate the zero-intercept. 20 degrees x 20steps/degree = 400 steps (in the negative direction since we’re calculating the zero temperature intercept) giving a focus intercept of position 1000 - 400 = 600. This would be the compensated focus point for zero degrees and the zero intercept. This only needs to be done once(for absolute focusers). With the zero intercept established, temperature compensated focus can be established easily using y = mx + b where “y” is the focus position desired and “x” is the temperature, and “B” is the intercept, 600 in this case. This simple calculation would allow setting initial focus to an accurate temperature compensated starting place.

Example: Using the same intercept and coefficient above, let’s say that I ended the previous night’s session at 5C. The focus position would have been 700. But when I start tonight, it is 24C. Instead of tweaking the focus manually to get it close, I can just calculate the temp compensated position: y = (20)(24) + 600 = 1080. This would put focus very close - close enough for AF to work well.

Anyway, this is not an earth-shattering feature request, but it would go a long way to making SGP start unattended more successfully.

Tim

4 Likes

Tim,

I fully support your feature request. Since v3.0.2.81 (May 2018) temperature compensation in SGP is working as expected. At present I calculate the starting focus position from the temperature (if don’t forget about it). Why shouldn’t do SGP this job, it would be much more reliable.

+1

Bernd