With temperature compensation enabled, SGP checks between frames whether the focus position has to be corrected for temperature change. At present, corrections as small as 1 step are applied, if necessary with backlash compensation. This is unnecessary. We want corrections only be applied, when the Critical Focus Deviation [CFD] of the scope is exceeded. Furthermore the permission of smallest corrections may result in very frequent movements of the focuser, if the worst comes to the worst, after each frame.
This all was brought forward in a feature request that was put a year ago in order to fix this issue: Temperature compensate tolerance - Feature Requests - Main Sequence Software
Then the proposal was, to introduce an user-definable threshold of temperature and/or time in order to minimize the number of temperature compensation corrections.
Hereby I put a similar, but slightly modified FR:
Please introduce an user-definable threshold of Focuser position (number of steps) as the criterion instead.
Why do small and/or frequent focuser movements matter?
They are unnecessary and can cause complications: The worst case is when you have a focuser with a very large step resolution. Assume that the temperature is relatively stable. Smallest apparent temperature changes (actually noise of the temperature measurement) will induce corrections of 1 step. If these corrections happen to be in different directions, that will call the focuser backlash compensation. The focuser will be moving back and forth, again and again. Nobody can cause me to believe that this situation is favorable.
I’ve been using Innovation Foresight’s ONAG SC with Optec FocusLock. This
system provides perfect focus under all conditions.
I believe SGP can replicate this excellent feedback system in software. The
challenge is to know what direction to move the focuser. Optec knows this
from the signed distortion introduced by the ONAG. SGP would need to watch
FWHM and reverse direction if it sees it increasing. Some initial
calibration feature may be used.
In other words…
The full star field is used to obtain a focus indicator, just like the
IF ONAG (which currently only uses one star).
Feed the focus indicator into the Optec FocusLock algorithm. This
algorithm uses a low-pass filter with a user-programmable stop gap (to
prevent a focus changes until FWHM exceeds a threshold) and an Averaging
Constant to control the number of frames used in the average.
I’ve been using Innovation Foresight’s ONAG SC with Optec FocusLock. This
system provides perfect focus under all conditions.
Yes, very nice. What is the connection to temperature compensation? Can we please stay on track?
Temperature compensation is already a feature of SGP, but unfortunately one that does not work correctly. Gary’s proposal is intended to initiate a fix.
THIS is a Feature Request, please don’t answer if you want to talk about Innovation Foresight’s and Optec’s products. Just make up a new thread, please.
Temperature compensation is not needed if this new system is implemented.
IMHO, this is the only solution for extremely precise focusing. Temperature
compensation doesn’t accommodate many optic issues.